1 Foundations, Basements, Crawl Spaces
Foundations take many forms, including full basements, piers, slabs, and crawl spaces. They need to be strong enough to hold up the structure, built on solid ground to avoid sinking or shifting, and protected from frost, soil and water pressure. They should be constructed in ways that help keep the house comfortable, and, when possible, provide extra space for living and for storage.
Much can go wrong with a foundation. But as you read through this chapter, you’ll see that similar problems keep repeating themselves: the foundation backfill is improperly done; the soil around a foundation is not properly graded or drained; the concrete is not properly cured; incorrect methods and materials are used for insulating, painting, and other finish work. Repetition is necessary because these problems manifest themselves in many ways.
Foundations for New Houses and Additions
The best time to avoid problems with foundations is while they are built. It’s much easier and less expensive to avoid moisture problems, in particular, with proper design than it is to fix them later. And if mistakes are made, it’s probably easiest to fix them (and perhaps to hold the contractor accountable) when the house is new. The most common serious mistakes are improper backfilling of the excavation, including provisions for a working and long-lasting drainage system and grading of the soil—which should always slope away from the house. There are also unique problems with new foundations. They include taking precautions for proper curing of poured concrete walls or choosing the right size concrete blocks for the depth of the excavation (too often, 8-inch blocks are used for foundation walls deeper than 5 feet). Once built, other problems are related to moisture in the concrete walls and floor of a basement, which may take as much as two years to dry and can cause considerable moisture problems in the living quarters.
Q. I am building a house this summer. It will have a walk-out basement, which will be finished with living space. Do both sides of the concrete foundation need to be insulated? Should footing drains be on the inside and outside of the footings? What is the sequence of materials for the drain: Does the fabric go down, then the stones, the drain pipe and sand? What kind of fill do I need to backfill with to make sure my concrete walls don’t crack? What is the ideal distance from the top of the concrete wall to grade? Do I need at least 4 feet of concrete below grade?
A. Let’s start at the beginning. Frost walls should be below the frost line of the area where you are building. The recommended practice in your climate (Northeastern U.S.) is to have frost walls a minimum of 4 feet deep below grade. It is best to have about 1 foot of the foundation above final grade but you must plan for the final grade to slope away from the house by 2 inches per horizontal foot. Concrete walls can be insulated from the outside or the inside; there is no need to do both.
Drain pipe should be installed next to the footings and not on top of them. The best procedure is to lay a 4-foot-wide band of geotextile (filter) fabric against the excavation wall (pin it with 16-penny nails) and place 2 inches of egg-size stones in the bottom of the trench. (If stones are expensive or hard to get in your area and recycled rubber tire chunks are available, they are a better alternative anyway.)
Now lay perforated pipe, holes down, over the stones; place at least another foot (preferably 18" or more) of stones over the pipe; fold the fabric over the stones bringing it up against the foundation walls and tape it to them to hold it in place until further backfilling.
Complete the backfilling with coarse sand or bank-run gravel to within a foot of what has been determined as the finish grade to ensure good drainage and protection against frost pressure. Complete the grading with topsoil. The only time it is advisable to install footing drains inside the foundation as well is if there is a seasonal high water table or very heavy soil.
Q. I am going to have a house built this summer and would like to know which type of foundation is best—poured concrete or blocks?
A. Either type is fine as long as it is properly sized. For instance, if a foundation is going to be deeper than 5 feet into the ground, 12-inch blocks should be used. You may have to insist on it, as many masons simply use 8-inch blocks.
Poured concrete foundation walls are generally 8 inches thick unless special conditions dictate that they be thicker. Steel reinforcement depends on the depth of the foundation, the soil pressure it has to bear, and other local conditions.
The most important thing is the backfill of the excavation against the foundation. It should never be done with heavy soils. A perimeter drain should be installed next to the footings; the crushed stones surrounding the drain pipe should be protected from silt with a geotextile fabric and the trench filled with coarse material. Heavy native soil should only be used to top it off and should slope away from the foundation.
Insulating a basement when remodeling
Q. I am remodeling my basement. I live in the northern part of Illinois where temperatures get fairly cold in the winter (approximately 30 F. to minus 10 F.).
I am replacing the paneling on the walls with wallboard. The 2-inch by 4-inch wall structure is in place with a 6mil plastic sheeting between the wall studs and the concrete foundation. I never get any water in the basement.
My questions are:
1.Should I leave the plastic sheeting in place and put batt insulation with paper backing facing the inside of the basement?
2.Should I put the batting all the way to the floor or leave a couple of feet for the warm air to penetrate to the outside to prevent freezing along the wall?
A. In answer to your questions:
Cut off the plastic at the grade line and hold it in place with a few tabs of duct tape. You only want the plastic to prevent any leakage from wetting the insulation but there should be some exhaust for any condensation, however minor it may be, to dissipate instead of remaining trapped against the foundation walls where mold could develop.
Use unfaced insulation and staple 6-mil plastic to the studs to provide the best vapor retarder possible. Any moisture in the room will easily bypass the Kraft paper, migrate through the insulation and find a plastic film in contact with a cool foundation wall. Condensation is likely to occur on the room side of the remaining plastic, where it will be trapped and wet the insulation.
Unless you know that there is a functioning footing drain and that the foundation was backfilled with stones and coarse material, and you make sure that the grade against the foundation is sloping away for good drainage, you should not insulate any lower than three feet below the outside grade level. This is to allow some heat loss through the foundation to keep frost at bay so it won’t crack your walls.
Q. We plan on building our raised-ranch house in the near future and would like to know the proper method of preparing for the pour of the lower-level concrete slab. Should sand be used as a base and be tamped before the slab is poured? Should a 6-mil plastic sheet be placed over the sand? How thick should the slab be? Should an interior perimeter drain be used?
A. Egg-sized crushed stones (or if available in your area, chopped tires) should be used instead of sand in order to promote lateral drainage and prevent capillary attraction, two features that sand does not provide. The stone bed should be a minimum of 4 inches and preferably thicker; it should be at least flush with the top of the footings, which are usually 8 inches thick.
The thickness of the stone bed will then be determined by the method of preparing for the footings which may be dug into the bottom of the excavation or formed on top of it (4 inches of stones are okay in the former but 8 inches should be used in the latter case). A 6-mil plastic vapor retarder should be placed over the stone bed and an inch of crusher-run (a by-product of stone crushing) spread over the plastic to promote proper drainage of the concrete as it cures. Failure to do this may result in dusting of the concrete later. The slab need not be thicker than 4 inches. In lieu of crusher run, 1-inch extruded polystyrene can be used, providing slab insulation as well.
Whether you need an interior perimeter drain, in addition to an exterior one, is determined by the wetness of the site, such as a seasonal high water table.
Q. Would we be better off having a basement built under our eventual modular home or a crawl space at a much lower cost?
A. Basements are always useful and a lot more convenient for access to mechanical systems that are often relegated to crawl spaces, where they are harder to service or maintain. Basements are also generally more healthful, as crawl spaces tend to become damp unless they are properly built.
Basements can also be used for storage or workshops and can be finished as living quarters if the family expands, as long as windows meet the emergency exit code. You will pay more now but will probably find the house more saleable, and may recover more than the difference in cost between a basement and a crawl space.
Blocks vs. wood for exposed basement wall
Q. We will be building a ranch house with an exposed basement. We plan on finishing the basement later and having a sliding patio door and a window installed.
Would the exposed basement walls be better built of blocks or wood? Will the weight of the house cause the wood wall to settle? What about cost differences?
A. Any walls out of the ground are better built of standard framing construction because it allows for better insulation. In your case, it will also make it easier to install the patio door and window later on. Their rough openings should be framed in now to make it even easier and cheaper to do later.
The weight of the house should not cause the wood wall to settle if the foundation supporting it is adequate. There is likely to be minimum shrinkage of the wood members as they dry. You should use 6-inch studs anyway to provide better insulation.
Q. I plan to add another room to double the size of our cabin up north. It is built on a 4-inch floating concrete slab. Should we first pour a footing and then pour the floor? Or should we simply pour another 4-inch floating slab to match the existing one? And, should the two be tied together?
A. It’s usually best to use the same construction technique as exists, if it has proved successful. Be sure that you also match what’s below the slab, i.e., the same thickness of crushed stones or whatever was used.
Yes, the two should be tied together by drilling holes 2 feet on center half way down in the edge of the existing slab where the two will join and tapping ½-inch reinforcing rods at least 6 inches in and sticking out 6 inches also. When the new slab is poured, the two will be bonded.
Another way is to undercut 6 inches of the existing slab and fill it with concrete as the new slab is poured.
Planter next to foundation
Q. Can a planter made with pressure-treated logs be used around the foundation for raising the grade, a procedure you have recommended often as necessary to keep a basement dry?
A. No way! I recommend sloping the ground away from the foundation. All you would be doing by building a planter would be creating a higher flat flower bed. The only time a raised planter is recommended is if the footings are not deep enough and subject to frost heave. This adds protection, but the planter should be under a broad overhang to keep it from getting wet.
Plastic on top of soil
Q. I have removed flower beds against the house and plan to replace them with decorative chips after raising the grade so it slopes away from the foundation. What’s the best soil to use, how steep should the grade be, and can plastic be laid on top of the soil and be covered with the chips to prevent weeds from growing?
A. I usually recommend a 2-inch slope per foot extending a minimum of 4 to 6 feet away from the foundation to prevent water pockets on grade, then the slope can flatten out. The best ground cover is grass. The type of soil, in your case, doesn’t matter since it will be covered with plastic. Plastic will not just prevent weeds, but also prevent percolation.
Q. I remember reading in your column about using a 2×4 to check the grade around the house for proper drainage. That is all I remember. Could you please fill in the blanks?
A. Try to use a full-length, 8-foot 2×4. If you place it on the ground perpendicularly to the foundation, it will tell you instantly if the grade is negative (leans toward the house), flat (also undesirable), or positive (slopes away from the house). Place a level on the board, if you’re in doubt.
It is quite difficult to eyeball for proper grade with mulch, plantings, and even grass against and near the foundation. Obviously, any flat or negative grade is best corrected to encourage water to flow away from the foundation.
Foundations are under constant pressure from the earth that surrounds them, which can change with the seasons. Sometimes, even tough materials and structures wear out. Failure to notice and address these issues early on can result in serious damage to a house.
Basement walls bowing inward
Q. Our 30-year-old home was built on a cinderblock foundation. Three years ago, while we were adding two rooms to the house, one of the severely bowed walls was completely straightened out. Of the three remaining block walls, two have a slight bowing involving only about five blocks in the middle of the wall while the third one has a more severe problem involving about 15 blocks in the middle of the wall, beginning at about four blocks up from the cellar floor.
I feel if it took 30 years for the wall to move this far and it hasn’t caused any apparent damage inside to the plaster or the outside of the house, it may not be worth undertaking the major task of digging out and trying to get the blocks back into place. Any suggestions?
A. Walls bowing inward do so because of frost or fluid pressure against them. The severity of the bowing and its location have a lot to do with whether or not remedial action should be taken.
A slight bowing may be ignored but should be watched carefully. However, if the wall is bowing significantly, i.e., it shows horizontal separations between the block of ¼ inch or more, or vertical displacement exceeding 1 inch or so, something should be done about it, particularly if it happens to be supporting the weight of the floor joists and the roof.
Gable walls, for instance, are often self-supporting whereas the front and back walls of a house usually support the floors and roof. The fact that it took 30 years to get to that point is no assurance that the walls won’t jackknife suddenly and bring about the collapse of the building.
There are several ways to proceed to repair the problem:
- As a precaution, support the first-floor joists near the damaged bearing wall sufficiently to carry the weight of the house bearing on that wall. Excavate carefully outside and attempt to bring the walls back into line (or replace them). Install a perimeter drain built of a perforated plastic pipe buried in an egg-sized crushed stone (1½-inch diameter) bed covered with a geotextile fabric filter. Backfill with coarse sand or bank-run gravel to near original grade. Finish the grade with native soil sloping away from the house no less than 2 inches per foot for as far away as possible. Plant grass and avoid flower beds against the foundation. The perforated pipe should be connected to a solid pipe that should come out to daylight down a bank or connect to a sump pump inside the basement.
- Reshape the grade around the house, including all appurtenances, such as walks, patios, stoops, etc., so that water drains away as indicated in the paragraph above, and build a new concrete-block wall against the severely bowed walls in the basement. This is done by drilling holes in the concrete slab every foot to insert ½-inch reinforcing steel rods in it, followed by setting 12-inch blocks over the rods, and filling the spaces between the existing wall and the new wall as well as the cores within the blocks, with pea-gravel concrete as the wall is going up. Where the existing wall is a bearing wall, the new wall must also be bearing and must be locked in at its top with a steel angle iron fastened to the underside of the floor joist with lag screws to prevent it from being pushed out. This is cheaper than doing the job from the outside, particularly if the old walls must be rebuilt. A competent masonry contractor can easily handle it.
- Have a house mover support the house, remove all the damaged walls and replace them with reinforced concrete walls. The same instructions regarding footing drains, backfilling and final grading apply.
- Call in a specialist in this type of repair who will place a steel plate against the bowed wall. In the center of this plate, there is a steel rod that goes through the wall and is anchored below grade outside to a “dead man” some distance away. A nut on the rod is tightened until the bowed wall is straightened out. The Grip-Tite wall anchor system is available nationally.
Sinking of slab outside of foundation wall
Q. Years ago, I poured a 2×6-foot concrete slab against a part of the foundation wall of my 50-some-year-old house to direct water away from it. At that time, it was sloping away from the foundation but, now, it has dropped about 3 inches and water leaks down the side of the basement wall finished as part of a rec room. Does this indicate damage to the basement wall? Should I take down the rec room wall?
A. The first thing you should do is to raise this slab back so it slopes away from the foundation again. A contractor should have little trouble doing that. The hollow beneath it should be packed solid with dirt tamped down. If you prefer, you can form and pour another slab over this one to reinstate the slope.
However, if your sketch is correct, I think that the original slab dropped because the dirt beneath it was puddled and compacted by the water from the downspout you show there. If this is correct, you should raise the grade to slope away, put a concrete splashblock under the downspout shoe, and make sure that the water is directed away or you may get a repeat.
Unless the rec room wall is insulated with mineral fiber, there should be little, if any, damage; it will dry in time. And even if there is fiberglass insulation, since it is not absorbent, the water should run down the fibers to the bottom of the wall. Just look for signs of progressive deterioration before you tear down the rec room wall. You may not need to do anything with the wall.
Crack in basement floor of three-year-old house
Q. We had a house built three years ago. The concrete floor in our unfinished basement has a large crack across it, approximately 1/8 of an inch wide. Is this something that I should be worried about? Is there something we should be doing to seal the floor? We do not get water or anything coming up the crack.
A. If the crack is straight, it may be following a control joint. This is a common practice in large expanses of concrete to allow for shrinkage that occurs as concrete cures. This should not be of concern unless the concrete shows vertical displacement (one side of the crack is materially higher than the other).
If the crack is irregular, it may also be due to shrinkage during the curing process because no curing agent or other shrinkage control was used—and no control joints were included as they should be in any expanse larger than 20 feet by 20 feet.
Again, if there is no vertical displacement this should be of no concern, but the crack should be filled with a concrete slurry. If there is material vertical displacement (more than 1/8th of an inch), you may want to have a contractor look at it to determine if there is a substantial settling problem.
Q. One of our basement block walls developed a horizontal crack and a slight bow along its full length. The soil around here is heavy clay, so we had it removed and replaced top to bottom with pea stones to relieve the pressure.
The wall is no longer bowed but the crack comes and goes, disappearing in summer and reappearing in winter. Our contractor wants to install seven steel beams but the insurance inspector says they are not needed.
A. Unless there is a way for water that may build up in the pea-stone backfill to drain away, it can freeze and put pressure on the wall. It is also possible that the clay is still pushing against the stones as it expands in winter. Try covering the pea stones with a geotextile fabric topped with a minimum of 1 inch of coarse sand. Add topsoil sloping away from the house for several feet if there is room to add it between the present grade and the siding, respecting the local building code requirements for clearance.
Depending on how you can accomplish that, you may be able to keep the clay drier and reduce the pressure it exerts on the block wall.
The beams do not appear to be necessary and would probably not help. Soil and frost pressures are irresistible; the blocks are likely to bow between the beams.
Q. The blocks of the basement walls of my 30-year-old house are starting to be pushed in. I was told that I could use steel rods and concrete in the hollow of the blocks about every 4 feet to reinforce the walls. Is this safe? Or will it put a lot of pressure on the footings?
A. Whoever told you that has little practical and technical knowledge. How do you insert the rods and pour the concrete without tearing the walls apart? If the buckling is minor, it may not need any repairs but it should be watched and the size of the cracks measured several times a year to see if there is further movement.
But what you must do is correct any grade problems around the house foundation that may hold or trap water and allow it to percolate in the soil and freeze, exercising pressure on the walls and causing them to crack and buckle. That goes not only for the soil but also for any structure such as patio, walk, stoop, driveway, etc., that does not shed water away from the house.
One problem area I see so often in my inspections is sunken ground under decks and porches that trap water. These hollows should be filled, however difficult it may be. Correcting all these problems so water flows away instead of soaking the soil should relieve the pressure exercised on the walls by wet soil freezing and expanding.
However, if the buckling is severe enough to warrant corrective action in order to prevent collapse of the affected walls, the least expensive way to achieve this is to build another wall in front of each of them.
Holes are drilled in the concrete slab every foot to receive ½-inch re-rods, 12-inch hollow blocks are threaded over the rods, concrete is poured in the block cavities and between the old and the new walls as the walls go up and the new walls are pinned to the floor framing at the top with steel lintels. A competent mason should know how to do it. Don’t worry about the pressure on the footings.
Repairing a long crack in the wall
Q. Our house was built 45 years ago. About 20 years ago, a horizontal crack appeared on the 10-inch-thick concrete block basement walls. It runs for about 35 feet, six courses from the floor, and varies seasonally from 1/16-inch to 5/16-inch, depending on the wet and dry spells.
The basement and wall remain completely dry. I want to caulk this crack with a waterproof compound; what should I use?
A. Don’t! This would prevent it from closing, if you did it when the crack is widest, and it would open right up if you did it when it is at its narrowest.
What you should do is to prevent the soil from applying so much fluid pressure on the wall. Look for low areas against the foundation and add clean dirt so the grade ends up by sloping away at the desired rate of 2 inches per horizontal foot for as far back as 6 to 8 feet, if there is enough foundation wall showing to permit it. Dirt must not contact wood, and most building codes generally require that dirt be kept 8 inches away from it.
Plant grass; do not mulch. This will move water away from the foundation and keep the deep soil drier, reducing the fluid pressure of wet earth against the wall.
Q. I have two cracks in my basement walls through which water seeps when it rains. I have three estimates to repair the cracks. Two of them will put epoxy in the cracks from the inside. The third company said they would also put epoxy in the crack by the window next to the patio on the east side but they would excavate outside to the footing and apply silicone mastic in the crack in the front or north wall. They would also chip out that crack inside every 2 inches and inject epoxy in it.
All three prices are in the same range. I am very confused as to which one I should choose. Can you advise me?
A. You didn’t say, but I will assume that your foundation is poured concrete.
Before considering spending any sizable sum on the epoxy injections, I would suggest you go over the grade outside your house. Fill any depressions, correct any areas that either collect water or direct it toward the house.
Check the gutters and downspouts to make sure they are free-flowing and that all discharge from the downspouts is collected into a splashblock or pipe extension and flows away from the foundation. Raise the grade where needed so it slopes away from the house but keep soil at least 8 inches from any wood.
If your patio slopes toward the foundation, have it resloped so water drains away. This can be done with a new concrete topping, bricks or flagstones.
It is always best to take care of these conditions first; they are usually all responsible for basement leakage. You may find it stops the leakage and relieves pressure on the basement walls.
However, if you choose to go ahead with the crack filling, I would select the one who plans on excavating and filling the cracks outside and injecting inside. It sounds like a more thorough approach for the same price.
Crack in a concrete floor
Q. Our house was built two years ago. The concrete floor in our unfinished basement has a large crack across it, approximately 1/8 of an inch wide. Is this something that I should be worried about? Is there something we should be doing to seal the floor. We do not get water or anything coming up the crack.
A. If the crack is straight, it may be following a control joint. This is a common practice in large expanses of concrete to allow for shrinkage that occurs as concrete cures. This should not be of concern unless the concrete shows vertical displacement (one side of the crack is materially higher than the other).
If the crack is irregular, it may also be due to shrinkage during the curing process because no curing agent or other shrinkage control was used—and no control joints were included as they should be in any expanse larger than 20 feet by 20 feet.
Again, if there is no vertical displacement this should be of no concern, but the crack should be filled with a concrete slurry.
If there is material vertical displacement (more than 1/8th of an inch), you may want to have a contractor look at it to determine if there is a substantial settling problem.
Q. There is an old well room next to the house with a small access door in the basement block wall. We want to seal the wall and fill in the well from outside.
Will bricking in the opening make the wall strong enough to resist the pressure of the fill, and what type of fill should we use?
A. There should be no problem with the bricked-up access hole if you build it the full-depth of the block wall and the opening is bricked tightly on all four sides. Let the mortar set for a few days. Fill the well hole with any coarse material available.
I presume there is a cover outside over this well room and that the fill will not be subjected to wetting.
Rebuilding an old fieldstone foundation
Q. My old two-family house is in good, sound condition except for the cellar walls, which are constructed of fieldstones. These walls have deteriorated and are crumbling badly both inside and out. A contractor fixed them two years ago but they have cracked again. He has patched them up but says they were too pulverized for further repairs.
Large chunks fell out last winter and many cracks developed. I don’t want to face the expense of another contractor and have the same thing happen again. Can you advise?
A. A house represents a considerable investment; its roof and foundation are the most important systems ensuring its longevity. From what you describe, I would recommend that you have the foundation redone. This can be done in one of several ways:
- The house can be jacked up and supported on large timbers and cribbing while the old foundation is removed and a new one put in. Properly done, this can give you a dry concrete basement with more headroom and add considerable value to the house.
- Another method is to replace the old walls piecemeal in sections. This does not require jacking up the house but it must be done by someone experienced in this process.
- A third option is to build new block walls against the old foundation from inside. A competent contractor can advise you which is best in your circumstances.
Q. My city home has a poured-concrete basement. There is a plastic vapor barrier between the top of the concrete and the sill.
My cottage basement was built of concrete blocks and the builder did not put a vapor barrier on the top of the block wall. Should there be one? If so, can I use Styrofoam boards instead of plastic when I raise the cottage? I feel this would seal some gaps between the blocks and the sill.
A. Sill sealers are used to stop air infiltration between the masonry foundation and the wood sill of the house, which is known as the mud sill because it used to be embedded in a mortar bed to level out irregularities in the top of the foundation. The energy crisis of the early ’70s made us aware of the amount of air infiltration, and we began to use sill sealers made of cellulose between two thin plastic strips or fiberglass rolls. Later, better materials were developed that did not absorb water as the previous ones did.
You certainly could install one when your cottage is raised, but I hope you are not raising it just for that. If the cottage is for summer use and not heated in the winter, air infiltration at the sill should not be a problem. In any case, the appropriate product to use is one of the synthetic plastic sill sealers now on the market. Do not use rigid insulation board, as it would be crushed by the weight of the building.
Q. Our house is built on a concrete slab. It keeps shifting, which causes cracks in the wall and ceiling gypsum board. It also affects the functioning of doors and windows. The cracks have been repaired but they come back. What can we do to correct this problem permanently?
A. A shifting house with the problems you describe indicates that the foundation is on unstable ground, or is not deep enough to be unaffected by seasonal temperature and moisture changes.
A permanent solution may be expensive, depending on what is causing the problem, and would probably require building a deeper foundation under the perimeter of the slab.
Judging from the temperature tables of your area (Oklahoma), the frost line may require footings approximately 2 feet deep. If the slab was poured monolithically with integral footings, they may not be deep enough. The moisture content and type of the soil under and around the house also have some bearing on the situation.
Talk to a structural engineer who is familiar with local conditions to determine whether deeper footings are called for or whether simply installing vertical extruded polystyrene rigid insulation around the perimeter of the slab and buried a foot or two below grade would be sufficient. The insulation exposed above grade will have to be covered with an approved protective coating and flashed to the siding.
An alternative used successfully is to bury a 4-foot-wide strip of 2-inch-thick extruded polystyrene rigid insulation on a slant, starting at the base of the slab’s edge (which should be insulated as described above). Cover the insulation with soil and plant shallow-rooted plants, or spread shredded tire rubber mulch. This will stop frost penetration and keep the ground below the insulation frost-free.
Determining whether cracks are a serious problem
Q. Our one-story, three-bedroom home is about 42 years old. It has a poured foundation. There are two cracks in the foundation, one on the east wall and the other on the north wall. Are they serious? What can we do about them?
A. Foundation cracks can be serious, but most are not. Since I cannot determine whether or not your cracks are serious at this distance and with the amount of information I have, you should have an experienced and competent home inspector or a structural engineer look at it.
The size and shape of the cracks, the composition of the soil, and the grade around the house, etc., are all factors that determine whether the cracks can simply be ignored, should be filled with cement or caulked, or if more drastic measures must be taken.
Foundation cracks can also admit radon gas, if you are in an area that is prone to this type of radiation from the soil and rocks. It’s a serious human health hazard. Your state health department may offer testing kits.
Q. The two lally columns in our cellar, supporting the main beam, are 35 years old. In the last few years, rusty water seems to come out of several holes that have developed in the columns. Is this what is known as rising damp? Does this present a hazard? Should I have them replaced?
A. Dampness is finding its way inside the columns. It may be that they are in contact with wet soil or that water has gotten into them from a repeatedly wet cellar. Whatever the cause of the rusting, the fact that the columns have holes, and rusty water is coming out of them, tells you that they have weakened considerably. You should not wait to take corrective action before they start crumbling and the structure above them starts to sag.
You haven’t mentioned whether there is a concrete floor, and whether the columns are encased in it. This makes a difference in the solution I will suggest. If there is a concrete floor, the simplest thing to do is to place a 4×4-inch pressure-treated post next to each column. Measure and cut the post exactly, jack (lift) the beam up about 1/8-inch, set the post in place, and lower the beam to put pressure on the new post.
Or, you can encase the columns with four pieces of 2×6-inch pressure-treated lumber, also installed with some pressure as detailed above.
If there is no slab, or the lally columns are sitting on it, and the columns are easy to remove, you may choose to support the beam while replacing the original columns with new ones.
Pressure-treated posts as a foundation
Q. I’m considering buying a camp on a lake shore and turning it into a year-round retirement residence but I am concerned about the construction. It’s built on pressure-treated posts which the present owner says are at least 5 feet in the ground and resting on large stones.
The building itself is only 6 inches above the ground so there is no space to crawl under. Is there a problem with this type of foundation? Will it last a long time?
A. If properly set in the ground as deeply as you were told and on stones large enough to offer adequate bearing on the soil on which the stones are resting, you should be all right. Probably, if on a natural lake shore, the ground is gravely, which should offer good bearing and drainage.
Try to find out if the posts were treated to a retention of 0.40 pound per cubic foot of CCA (chromated copper arsenate). If the owner can tell you where they were purchased, the supplier should be able to tell you if they stock only pressure treated lumber marked AWPB LP-22, which is for wood in contact with ground or water. If they only meet AWPB LP-2 standard, or 0.23 lb./cubic foot of CCA, that’s not good enough for in-ground installation.
Check inside the camp for settlement by looking at doors and windows: do they all open and close easily; is there sizeable variation in the reveal between doors and jamb when doors are closed; are the floors even?
Also look under the camp with a strong flashlight and check for the condition of the floor joists: Do they look healthy, or has the wood darkened substantially, and is there mold growing on it? In any event, the earth under the cottage should be covered with plastic to reduce moisture unless there is no skirting to prevent total ventilation.
Column supporting roof overhang is sinking
Q. We have a small overhang with a shingled roof and rain gutters in front of our house. The overhang runs over a two-car garage, the front door, and a small patio. The overhang is only about 3 feet deep over the garage doors, but over the front door and patio, it is about 15 feet long and 8 feet deep. The front door is set back from the garage.
There is one wooden column supporting the overhang at the farthest corner of the patio away from the house. The column rests on the concrete slab that forms the patio; the column is not supported by a concrete footer. Over the years, this corner of the patio has sunk approximately 4 to 6 inches. As a result, the roof line of this overhang sags noticeably from left to right and during heavy rains, water overflows the gutter in the low corner of the overhang. I have raised the gutter as high as I can in the corner, but it is still too low.
I would like to raise the low corner of the overhang so that it looks better and also eliminate or reduce the overflowing water problem. Can I raise this corner of the overhang and install a new column supported by a concrete footer?
A. Yes, you can raise the overhang and bring it back to where it used to be and you will need a footing or some other means of support down to below the frost line in your area. But why do you need a new column? Can’t you use the existing one?
You haven’t said anything about the sunken patio onto which the column is now sitting. Is it cracked or did it settle in one piece and pulled away from the house? This is not a job for a homeowner unless you have the necessary skills and equipment.
You may want to contact a mud-jacking contractor (look in your Yellow Pages under Concrete Contractors and call them to ask if they do mud-jacking or can tell you who does). However, the installation of a new footing is another matter and it may be difficult to provide under the circumstances.
Another option is to have a contractor licensed in the Grip-Tite Slab Pier System perform the leveling of the patio while at the same time using the Grip-Tite Foundation System to provide a “footing” for the column by means of a helical steel post that is driven down to the bearing capacity of the soil for the given condition. To get the name of the nearest Grip-Tite contractor, call 515-462-1313 or visit their Web site at: www.griptite.com. Study the process and if you are interested in it, click on Find a Contractor and scroll down to your state.
Q. We are looking into purchasing our first home and have found one we like, but it has a wooden basement. How durable are they? What should we check for and how safe is breathing the vapors?
The house is approximately 10 years old and the basement is unfinished with no windows. We’d like to turn it into a recreation area.
A. Pressure-treated foundations have been in use for many years in the U.S. and Canada. Properly built, they should be fine.
Since the house is 10 years old, you can easily determine whether the walls are straight horizontally and vertically (not showing signs of bowing).
There should be no vapors to worry about. Fiberglass insulation can be used to fill the stud spaces, a plastic vapor retarder installed over it, and gypsum board applied over the studs. Windows can easily be cut in the sections of foundation that are above grade.
Mortar deteriorating in a brick foundation
Q. Some of the mortar of the foundation of our 91-year-old house is soft and sifting out. The foundation is not cracked nor is it buckling or leaning, but some of the bricks were loose before I tuckpointed them. How can we decide if the foundation needs to be replaced?
A. I doubt very much if the entire foundation needs to be replaced since you have not noticed any problem; it probably needs only to be repointed, and that may need to be done in sections so as not to weaken it. Your safest bet is to call in an experienced mason to investigate and advise. Do it soon, before any more serious damage occurs.
Concrete layer crumbling from block foundation
Q. My home is 25 to 30 years old. The foundation is built with cinder blocks with a layer of concrete over the outside. This layer is coming off. What would be the best method of repairing it to avoid future problems?
A. All loose cement parging covering the blocks should be removed. You can purchase a mix of cement and sand in bags in hardware or building supply houses and mix it with water according to directions on the bag. It would also be wise to add to the mix a vinyl additive that increases the bonding to the substrate. You will have to wet the surfaces to be treated and trowel the mix on.
Unless you are pretty good at these repairs, you may be wiser to hire a mason. A poor job would devalue your house as it is very visible and it might not last long.
Repairing and finishing an older stone foundation
Q. The foundation stones of our circa 1900 house were cemented in, but the cement has turned to sand and dust and is sifting down to the basement floor. Is it possible to replace the cement and seal the rock walls?
I would like to finish off the basement to enhance the space and save energy, but I’ve heard conflicting arguments about sealing off rock foundations from the heat of the house. Foam panels on the outside of the foundation walls are a future goal but not for several years.
A. Yes, the old mortar can be removed by scratching it out with an old screwdriver or masonry chisel. But be careful not to remove too much of it, as this might cause the stones to shift. Clean the joints with a soft brush, make a stiff mix with a pre-mixed mortar such as Sakrete, wet the joints and stones to be re-cemented according to directions on the bag, and point them up.
Then coat the stones and mortar joints with Masonry Lusta to seal them. You may want to hire a mason to do this as it sounds as though you have a major job on your hands, and it would help to hire someone experienced in this work. It’s often cheaper than correcting mistakes later.
It is not safe to insulate a foundation any deeper than 2 feet below grade if the soil against it is clay, if you’re not sure there’s a footing drain that’s working, and if the grade and all appurtenances to the house are not sloping away from the foundation to shed water away from it and not toward it.
Q. The cement blocks in one wall of our foundation are deteriorating and crumbling away little by little. This is the wall common with the attached garage and it seems the deterioration is caused by salt that has seeped into the wall over time. The house is 30 years old. We have been unable to locate anyone who has seen this problem before or has any idea how to fix it. Any suggestions?
A. Your diagnosis is correct; salt brought in by the cars and running off toward the affected wall is responsible. I have seen this problem in houses where the garage slab was not properly pitched to the doorway but tilted toward the house wall. The area of the slab near the affected wall, and the bottom of the wall, should be thoroughly cleaned with a solution of TSP-PF or equivalent strong detergent, rinsed, and allowed to dry completely.
Have a mason build a cove along the joint of the slab and the wall with Portland cement mixed with an additive that promotes bonding. The cove should be sealed to protect it from salt damage. The purpose of this cove is to keep salt water from reaching the wall and causing further deterioration. This is less expensive than pouring a concrete cap over the slab to establish the desired drainage.
The mason should also clean and wire-brush the damaged blocks in the basement, and coat them with the same mixture to repair them.
Q. Our 22-year-old one-story house sits on a concrete-block foundation. The faces of several of the blocks have crumbled and fallen off in places. How should they be repaired?
A. The spalling is probably due to the blocks absorbing water, which then freezes and causes the blocks’ faces to pop off.
Dig down a foot or so and see how the blocks look. If they are wet, that probably is the source of the problem. Dig down deeper, approximately 2 feet.
Wire-brush the exposed blocks to remove loose materials, and coat them with waterproof cement or Thoroseal Foundation Coating. This parging should be applied in two coats. Lay black plastic against the foundation, and then backfill. This should break capillary attraction in the most vulnerable area.
Maintenance problems with cinder-mix walls
Q. I need help with a problem that has plagued me for some time and requires repairs every summer. Our foundation is not made of blocks but of a poured cement cinder mix.
Every winter, the surface of the foundation chips off and I have to patch it, waterproof it and paint it. I’d like to cover the existing foundation with anything that would not need repeated repairs. Any suggestions?
A. Cinder blocks or cinder mix are not as resistant to moisture absorption as concrete blocks or poured concrete with stone aggregate, but they were widely used some years back. You have two options that should solve your yearly maintenance problem.
One is to have a competent mason remove all loose material from the surface of the foundation and fasten galvanized metal mesh to it. This is followed by the application of parging the way it used to be done prior to the “dumbing” of the trades as a friend refers to the taking of short cuts so common nowadays. A scratch coat is troweled on, followed by two coats of Portland cement.
This should be done not only on the part of the foundation above grade but at least 2 to 3 feet below grade at which point the bottom should be tapered so as not to be “caught” by heaving ground. A sheet of 6-mil black plastic should be applied from grade down past the termination of the parging to act as a slip sheet and further protect the foundation from moisture absorption.
The other solution is to have a carpenter install ½-inch-thick pressure-treated plywood over the exposed foundation and at least 2 to 3 feet below grade. The buried part should also be covered with plastic. The top of either system should be properly flashed to the siding to prevent water from getting behind.
Whitish dust from concrete blocks
Q. There is a whitish dust on the bottom cement blocks of my basement. What causes this and what can I do about it? I would like to paint the cellar walls.
A. The efflorescence is due to salts in the blocks and mortar that were dissolved by moisture and left on the surface when it evaporated. It can be removed with a stiff brush used dry or with water. It indicates moisture penetration, but causes no harm. You should remove the source of moisture which is likely to be coming from poor grading around the foundation or the problem will continue.
The only coating likely to stick is one with a cement base. But you should not waterproof block foundations from inside. Water would build up inside the cores and cause serious problems in the living floors as it evaporates.
Sandstone foundation is crumbling
Q. The foundation of our 45-year-old house is built of sandstone blocks and is starting to crumble. What can we do to stop this disintegration?
A. Have a small area, approximately 1 square foot, of the foundation washed with the most powerful jet you can achieve from your garden hose. Rub your hand on it once it is dry to make sure all loose material is gone. Apply a mixture of equal parts of Thoroseal or Thoroseal Foundation Coating and Acryl 60, and partially embed in it a piece of fiberglass tape such as the type used to tape drywall joints, leaving 6 inches of it sticking out. Wait a week and yank the tape out.
If only the tape comes out, the substrate is probably strong enough to receive a coat of the mixture after a thorough washing of the entire areas to be treated. If you use a pressure-washer, use the gentlest setting to avoid damage to the foundation.
Your choice now is between Thoroseal, a decorative and pigmented coating that comes in a variety of colors, or Thoroseal Foundation Coating, which is pure cement without pigments and not as attractive or even-colored. Otherwise, the two products have the same basic formulation.
However, if the entire patch comes off with the tape, the substrate is not sound enough to apply the cement mixture successfully. In a couple of years, it will fall off in chunks. In that case, you have two choices.
You can coat the sandstone blocks with Thorosilane, a clear silicone water repellent that will preserve the appearance of the blocks while preventing the absorption of water, the cause of your present predicament. This should be repeated every three to five years. Or you can coat the blocks with Thorocoat, a non-cementitious coating that will hide the blocks as it comes in pigmented form only.
You may need the services of a competent mason.
Water and Moisture Problems in Foundations
There are several sources of water in basements and other foundations, some of which are unavoidable. The most common serious water problems by far are from surface water seeping through because the soil is not properly graded away from the foundation. Less common but also serious problems occur from underground water supplies. Crawl spaces with dirt floors cause moisture damage to a house if the soil is not completely covered with plastic sheeting. But even a well-designed basement may have moisture from sweating pipes and condensation from humid summer air.
Q. We moved into our new 1,450-square-foot ranch in November. We were told by our builder that it would take the winter for the concrete to properly dry out. We’ve kept a window slightly open in the unfinished basement as well as windows in the kitchen and the bathroom at night. We have two dehumidifiers going all the time since the weather got cold (one in the basement and another upstairs) and also keep the main bathroom fan going all night.
In spite of all of this, I have to dry all the windows of the main floor every morning. The lower, unused level is okay. Shouldn’t this problem be clearing up by now? If not, how many winters is it going to take?
A. Sometimes it takes two heating seasons for a new house to dry completely. Much depends on the temperature at which you keep your house during the winter and the amount of moisture your family generates.
For instance, if you are a family of four, a 1,450-square-foot ranch house is not very large and the family daily activities—such as bathing (especially if you take long showers) and cooking—generate a lot of moisture in the house. If you add water-loving plants, pets, and, perhaps, improperly-vented dryers or bathroom and kitchen fans, you have a problem.
Bathroom and kitchen fans should be vented to the outside through walls—not through the roof, into the soffits or the attic, or into a ridge or gable vents. You should check that this has been done correctly as too many builders just terminate the vents in the attic or other wrong places—a serious mistake particularly for kitchen fans that can throw grease in the attic where it can ignite if a fire starts on the stove.
The fact that you do not have moisture in the basement is most likely due to your having several windows open. The open basement window lets in colder and drier air to replace the warm, moist air escaping through the upstairs windows and bathroom fan.
But the fact that you still have the problem upstairs also tells me you may generate too much moisture.
Dehumidifiers are not very effective in the winter, particularly in a cold basement, and cost a lot to run.
Remember also that houses collect a lot of moisture during the humid days of summer and it takes several months of the heating seasons to reduce the level to the point where you no longer get condensation on windows.
If you still have the problem next winter, you may need a whole-house air-to-air heat exchanger.
Repairing foundation problems that were hidden by house seller
Q. I purchased a house about 8 years ago. After I moved in, I discovered the basement retained water, this was a question I asked the seller before I purchased the house, who said it did not get water.
I had an inspection done before purchasing, but the seller did a good job of hiding the fact. In any case, I finally saved enough money to have French drains put in. The contractor advised me to take the drywall off the wall in the basement, in case there was any mold (putting up this wall was one of the ways the seller hid a defect in the foundation).
When I took the drywall down (it was the only wall the former owner had drywall on), I discovered a bulge and a shift in the foundation of approximately 3 inches out and approximately 6 feet long. How do I go about repairing this problem?
A. First, you have a claim against the former owners; sellers are required by law to divulge defects, and not only did they not divulge the leakage and wall problem, they lied when you asked them! The real estate agent may also bear some responsibility but that is questionable. Finally, did the inspector miss something — such as water stains at the base of the gypsum wall (unless the wall was installed just before the sale and no leakage occurred after that).
There could also have been some other signs but, unless you have photos taken at the time of the inspection, it may not be possible to prove that there was something suspicious on the wall after eight years. The training and experience of the inspector are always very important in hiring one.
The surest way to get an experienced inspector is to look for one who is a fully certified member of ASHI (American Society of Home Inspectors). To find one, visit ASHI”s Web site at: www.ashi.org and follow the prompts under “Find a Home Inspector.”
A 3-inch displacement in what I assume is a block wall is quite serious. If it is on a bearing wall, it can lead to structural collapse. This is not something for you to fix yourself. You need to have an experienced contractor (or an experienced mason) investigate the best procedure for repairs. The fact that the bulge and shift are only six feet long is a plus, and it may make the repairs easier and less costly. When you have all the answers, decide whether or not it is worth talking to an attorney.
Stopping seepage into basement
Q. I get seepage in my basement when it rains for several days. It forms a large puddle on the floor. I bought the house knowing this defect two years ago. I have tried several times patching up the two pin-size holes in the foundation but the water always manages to get in and I have to use old towels to dry it up. I have used Quickrete Water-Stop Cement and waterproofing paint but the water stills gets in. Is there any material to stop the leaks?
A waterproofing contractor came to my house for an estimate and he suggested installing a sump pump for $3,000 but part of the stairway would have to be removed to accommodate the pump. What advice can you give me?
A. The product you used should have worked. There are others that do the same thing. Did you follow the instructions carefully?
I am not clear as to whether the leakage occurs only through or around the two holes in the wall and not also at the joint of the foundation wall. It sounds to me as if you have a grading problem. Check around critically, as I have seen water come into a basement from a long distance away. One unusual case occurred when a dog had dug a hole under a bush to keep cool. A nearby downspout discharged roof water that filled that hole, and the water traveled to the opposite side of the house until it found a weak spot.
Ductwork sweats and drips
Q. The warm-air furnace with air conditioning is in our basement. In the summer, there is a severe and intolerable damp mildew smell in the basement. The ductwork closest to the unit sweats and drips onto the floor and we believe that this is the origin of the odor. Is there a way to remedy this smelly problem? We have bought a top-of-the line dehumidifier but it has not taken care of the problem.
A. A dehumidifier would be the solution I would suggest but since you have one and it does not take care of the problem, you should have the plenum on top of the furnace and all accessible supply ducts in the basement insulated.
Obviously, your condenser is fully-charged and operating efficiently, thus sending very cold air through the plenum and the supply ducts. Insulating these ducts would push the problem further down the line but the inaccessible supply ducts to the first floor registers are very short.
Those to the second floor (if your house has one) have such a small cross section that the cold air going through them would cool the surrounding area enough to prevent the dew point and condensation.
Waterproofing a finished basement
Q. I read your article on dry basements and am wondering if you can help. My basement block has been treated with DryLock, but the back portion of the basement is filled with stains and efflorescence. Alas, the water is coming from my 2000-square-foot blue-stone patio. I believe that the blue stone is hollow in spots and accumulates water, which then pushes its way to the wall and down the block.
I have called basement waterproofing companies and they talk of digging up and applying pipes all over the basement. This makes no sense since the basement itself is dry and the drainage system around the basement floor is fine. The front of the house, which is graded correctly, has no efflorescence problems. We would like to finish the basement and avoid any major future problems. Can you tell me what can be done so that the problem is solved without major expense and major damage?
The area involved is about 9 feet high and about 75 feet wide. I know you have suggested putting in holes every few feet at the bottom of the block and applying some kind of drainage system to a sump pump. My guess is that this would be rather unsightly. Can you make any other suggestions?
A. I am sure that the stains and efflorescence are caused by water filling all or part of your block foundation because the DryLock treatment prevents it from leaking into the basement; this is a prescription for a far more serious problem than the one you have now.
The holes I suggested to drill at the base of the mortar joints of the block walls in an earlier column are the best solution. But these holes must be connected to a drain system since the water problem is likely to go on until you fix the suspected patio problem. Waterproofing contractors install fiberglass channels and cut a hole in the concrete slab to install a sump pump. Obviously, since the blocks’ cores are probably filled with water now, drilling the holes into the mortar joints will cause leakage on the basement floor. A careful contractor will devise a way to control the leakage. But this is an expensive job.
As to the aesthetics of these channels, they look like an oversized baseboard and can be concealed within a wood chase when you finish the basement.
Moisture-proofing a concrete-block basement
Q. I would like to moisture-proof the basement to eliminate dampness and make the basement humidity the same as in the rest of the house. The house is 10 years old and has an unfinished basement six feet below grade. There are no signs of water seepage or wall cracks.
My plan is to apply two coats of Drylok, a rubber roofing membrane, and two layers of 6-mil plastic before studding, insulating and putting up drywall. Is this overkill? What is the best approach?
A. Yes, I would say this is overkill. Since you mention that there are no wall cracks, I assume that your foundation is built with concrete blocks. Just in case you haven’t seen my oft-repeated discussions about the problems with waterproofing a block foundation from inside, be aware that doing so invites water to fill the blocks because it cannot leak into the basement. This water evaporates into the building and creates a very unhealthy environment that includes molds, mildew, a bad smell and potential deterioration of the framing and finishes. Years ago, I worked on an apartment building that had to be vacated for that very reason.
I realize that you haven’t had any moisture problems or leakage yet but that does not mean that you won’t. Once the water is in the blocks’ cores you won’t be able to get rid of it easily and you won’t even know it’s there until too late. You must also keep in mind that insulating the basement walls may mean that the ensuing deeper frost penetration will cause the walls to crack.
Insulating any foundation walls safely requires an effective drainage system (for protection if the proper grading fails or the water table rises), backfill of the foundation with coarse material that will drain efficiently and not expand in freezing temperatures; and positive grading to drain water away from the foundation. In the case of a 10-year-old house where you may not know if there is a functioning foundation drain and what kind of backfill there is, at least make sure the grade slopes away from the house.
As to the best way to finish the basement, tape 6-mil plastic to the walls no higher than 2 feet below the grade line and drape it onto the floor by 5 inches; this will ensure that if you ever have leakage at the base of the walls (where it usually occurs), water will not wet the studs and will seep under the plastic. If water seeps, this will tell that you have a grade problem. Nail a pressure-treated plate to the concrete floor through the plastic. Stud the walls, but only insulate them from the top to no more than two feet below grade; the heat loss through the bottom of the walls will help keep deep frost at bay. Keep the bottom of the drywall an inch from the floor and install a wood baseboard with screws for possible removal.
Protecting basement from rainwater
Q. For some time we had water coming into the basement during rainstorms. When the house was built, about 35 years ago, the builder put a pipe system around the inside periphery to catch water and direct it to a sump pump. Over the years, this system apparently filled with silt and this, together with a drop in the grading, allowed water, at times, to literally pour into the basement at the window wells.
About two and a half years ago, we had a new system of piping put in including drains in two of the wells so that the water flowed through a drain into a pipe and directly to the piping around the edge of the basement and into a sump pump which has battery backup. This system solved the problem of water coming into the basement very well, but we began to see damp spots in the cinder block walls and evidence of mold. Last spring, we had the walls painted with Drylok waterproofing paint. This seemed to contain the moisture, but now we are seeing staining on the walls in some areas and flaking with efflorescence.
We are concerned with the possible health ramifications of this condition. We are taking steps to remedy the grading problem and hope that by directing water away from the foundation, this will also help.
A. Too bad you went to such an expense to have a new drainage system installed when re-grading would most likely have taken care of the water problem at considerably less cost. Drainage systems are an insurance policy against leakage if the grade settles over time and before it is repaired, and also in case of underground water sources. But proper grading is usually all that is needed to keep a basement dry.
For a drain system installed on the inside periphery of a basement’s foundation to stop working, it had to be connected to a similar drain system around the outside of the footings. Whether the silting occurred only in the outside drain system or in both the outside and inside systems, the results are the same. But water filling your basement window wells has to be because the drop in the grade you referred to is leading water into them — assuming that run-off from the roof is not involved. Re-grading outside when the weather permits should take care of that problem, as well as the problem of damp spots on the cinderblock foundation walls.
Painting the cinderblocks with waterproofing Drylok was, in my experience, a serious mistake. I have seen several cases where cinderblocks were waterproofed with various products without also making the necessary corrections to a negative grade. The result was that the cinderblocks filled with water and caused immeasurable damage inside the living quarters. The fact that you are seeing stains and efflorescence in some areas indicates that the block cavities are filled with water, and you have every reason to be concerned about any health effects.
At this point, the water in the blocks must be drained out and the only feasible way to do this is to use a star masonry drill (buy in a hardware store) and a hammer to punch holes manually in the vertical mortar joints at the base of the walls every couple of feet. Do not use an electric tool to do this, as the water will gush out as soon as the holes are punched through. Be prepared for a considerable amount of water draining out and resultant basement flooding unless you devise a system to contain the water in a channel along the walls and lead it to the sump pump.
Moisture builds up in remodeled house
Q. For 22 years, we have been living in a two-story home built around the turn of the century. Over the years, we have gutted and remodeled the interior, added a large addition, vinyl siding and, most recently (2 years ago) replaced all windows with high quality double-hung insulated windows with wood frames inside and vinyl clad exterior.
The insides of the windows were left natural and covered with several coats of polyurethane. At the same time, the bathroom (on the first floor) was also completely gutted and rebuilt with new walls, floor, ceiling and all new fixtures. Over the past two years, we have seen an increasing problem with moisture buildup on some but not all of the windows.
The big problem is in the new bathroom and upstairs bedrooms facing north. The windows in these areas are always moist during cold weather to the point that mildew forms on the wood frames and has to constantly be cleaned off. I am afraid this is affecting the wood and it will begin to rot. The bathroom is well ventilated with a high quality exhaust fan.
The cellar in this house has a dirt floor and a low water table. There is always water in the basement in the spring and I need to pump several times during spring thaw. My wife feels that the wet cellar is the cause of the problem and the cellar floor should be covered with crushed stone and plastic. This would be difficult because the ceiling in the cellar is only 4 feet high and there is no outside access except for two small windows. I disagree with her because the problem is only in certain areas and the rest of the windows are fine. Is it possible that the cellar is the problem and, if so, what is the best way to solve the problem?
A. Your wife is right. But there is no need to put crushed stones down; 6-mil plastic is enough. You may want to use two layers to be sure that, if anything on the soil punctures the lower layer, there is the top layer to keep the moisture out.
However, you need to control the water that gets in the cellar. This is best done by correcting any grade problems around the foundation and, if there are gutters on the house, by making sure that the downspouts lead water away from the house.
If you do not have gutters, make sure that there is some masonry (patio blocks, pavers, flagstones, etc.) at the drip line of the roof to prevent the formation of troughs dug up by falling water. The masonry you choose should be flush with the grade, which, itself, needs to slope away from the foundation by about two inches per horizontal foot.
Next, assuming water comes in at the base of the walls, make a small trench about three inches deep around the inside perimeter of the foundation walls and use the soil you remove to build a curb on the interior side of the trench. Lead this trench to a sump in the most logical part of the cellar (the best place to discharge the water outside). Dig a hole 30 inches square by 30 inches deep. Place 6 inches of egg-sized crushed stones in the bottom of the pit, put a 24-inch by 24-inch flue liner on top of the stones, and then fill the space around the flue liner with more stones. Install a high-quality submersible sump pump inside the flue liner, making sure its discharge flows away from the foundation so as not to re-circulate back into the cellar. Lay the plastic over the entire soil area of the crawl space but stop at the top of the curb.
Assuming that the cellar (which, at only 4 feet high, is really a crawl space), is not used much, there should be no need to protect the plastic from heavy traffic. But if there is need for frequent access to a furnace or anything else, it is advisable to put down some walking boards or use sneakers to walk carefully on the plastic.
By tightening the house over the years, and particularly by replacing the windows, you have reduced the movement of air through it, thus resulting in the accumulation of moisture. The reason only windows on the north side of the house are affected is because it is a lot colder on that side, and never gets the sun.
Water flowing over frozen ground
Q. Each winter for the last several years, there is water in the southeast corner of my basement. This happens only when the ground is frozen and we experience sudden mild temperatures with significant rain.
I have not experienced any water problems except under these weather conditions. I removed the gutters last year (they were very old) and the problem still exists. The grade around the east side of the foundation is level and the south side has a cement walk 2 feet wide and flush to the foundation. What do you believe is causing the problem and what are your recommendations?
A. What you describe is typical of what happens when water is not allowed to flow away from a foundation. With the ground frozen, the only way for water to go is down along the foundation until it comes into your basement. During the rest of the year, it seems that your soil is able to absorb the water and no leakage occurs.
The solution is to slope the flat grade gently (I recommend 2 inches per foot) and plant grass on it. Check the slope on the concrete walk; if it is not sloping away from the house and you still experience leakage after correcting the grade next to it, you may have to top it with bricks, flagstones or another layer of concrete to achieve the proper slope.
The fact that you removed the gutters makes it even more essential that rain and roof drainage be moved from the foundation as quickly as possible. Roof drainage can cut grooves in the grass, so you may want to insert patio blocks or similar masonry in the sloping grade and flush with the grade at the drip line of the roof to prevent erosion.
Raising the grade around basement windows
Q. We live in a six-year-old house. The grading has sunk around the basement windows and puddles form, causing leaks, not through the windows but just below them, at a joint in the masonry. A friend tells me that he feels the tar is not high enough on the outside walls and that the grading needs to be raised where it has sunk. Can you tell me what needs to be done?
A. Your friend is partially right—the grade should be raised in all the low spots but there is no need to raise the line of the foundation coating, as it is of dubious value. Instead, tape 6-mil black plastic to the walls from where the new grade line will be and down to a few inches overlap of the existing foundation coating. And now all you need is good dirt, a wheelbarrow, and to pin down your friend to an afternoon of work.
Snow-melt coming in through window wells
Q. The foundation of our 25-year-old house is low, and the window wells are recessed into the ground. As a result, we have a frequent problem with snow melt running into the window wells and into the basement.
We have tried to build up the area close to the foundation, but it hasn’t been very successful. What can we do to take care of this problem?
A. Assuming that enough of your foundation is out of the ground, you should aim to raise the grade so it slopes about 2 inches per horizontal foot for as far away as possible without having soil in contact with any wood.
I often see grade around foundations where people added dirt but still left it flat at the top. The object is to have a positive slope from the foundation on out, and it is best to plant grass on it and avoid flower beds close to the walls.
If the window wells, as is often the case, are lower than where the top of the grade should be, you should extend them but not lift them, as you want the bottom to stay where it is.
The easiest way to extend them is to dig a narrow trench, 4 inches deep, around the outside. Stand bricks upright in the trench, so their flat surface is against the well. Since bricks are 8 inches long, they will stick out of the ground 4 inches.
Pack the dirt back against them and add more to follow the rest of the grade line.
Window wells fill with rainwater
Q. For the past two years, during very heavy rainfalls, one of my window wells has been filling with rainwater which then leaks through the window frame into the basement. The house is over sixty years old; the window wells are concrete and rectangular-shaped. I have been unable to find the plastic covers in the proper size and shape. Please advise as to what can be done to alleviate this problem.
A. Is the window well filling with water from the roof, or is it under an overhang, or on a gable side of the house? The first thing to check is the condition of the grade around the well. If there are sink holes or the grade is generally negative (sloping toward the well), you need to repair it by adding soil so it slopes away from the concrete walls.
Well covers are usually only needed if the water from the roof falls into the wells. Otherwise, a well that is constructed properly, with good draining soil, should be able to take even heavy rains. But bear in mind that I haven’t seen your condition so I can only give you a few pointers.
If you do need a well cover, and since you cannot find the right size, you may have to have one built with plexiglass, or with pressure-treated plywood if cutting off the light to the basement is not a problem.
Moisture from basement of new house
Q. The foundation of our house was built last November, and the house is now complete. There is water on some of the basement walls. The builder says it is condensation from humidity. It is on the top of concrete basement walls for the above-ground portion. Is this common with new construction?
A. In this case, I agree with your builder. There is a lot of moisture in a new house, particularly in concrete, which is poured with twice the amount of water it really needs for curing. This additional water is needed to make the concrete workable.
Your house was built over the winter and the condensation manifests itself on the coldest parts of the concrete—those above ground. The condensation should clear as the weather warms up but keep in mind that it often take a couple of heating seasons for all the moisture from construction to evaporate. Do ventilate as much as possible.
You didn’t say where your house is. If it is in an area without air-conditioning and you rely on open windows in summer, it may even take longer as the very moist summer air is not conducive to much evaporation.
Water seeping into corner of basement
Q. We have a finished basement that has water seeping in at one corner. We looked into having an interior drainage system put in, but it is cost prohibitive. Someone recommended we install an exterior sump pump to draw the water away from the house. Have you ever heard of doing this and is it effective? Are there any other alternatives? And most importantly, how do we find a contractor that has experience with this kind of work? We would really appreciate your advice.
A. The first thing anyone with basement leakage must do is to check (or have checked by a knowledgeable person) the grade around the house. That includes any appurtenances such as patios, walks, driveways, etc. All flat or negative (sloping toward the house) grade must be corrected to shed water away from the foundation. This may require quite a bit of work if appurtenances need to be altered.
Not knowing your site, I can only say that whoever suggested an exterior sump pump has a great imagination. I have never heard of that before. Condo projects do have deep drainage systems if there is a lot of water to dispose of, but they generally lead to a ditch, a storm drain, or some other outlet.
Recommending a contractor to do corrective work is harder to do. It needs to be someone who understands these principles. It can be an excavator (I have worked with some who are savvy), a general contractor or a landscape contractor.
You may need to have a civil engineer or highly qualified home inspector survey your property and come up with recommendations and a plan of action. It is a good idea to have this person supervise the work as I have been involved in situations where I had written a very clear report with sketches and photos only to find out later that my instructions and design were not followed and needed corrections.
Concrete scaling on basement floor
Q. I need help. I have had my house from new. After four years, I used a good industrial oil-based floor paint on my cement basement floor. It was down for 20 years. Then I used water-based paint and it lasted 20 years. I wanted to get back to oil-based paint.I used as heavy-duty floor sander and took off much of the old paint.
Now the problem. In a few spots on the floor, by the cinderblock wall, the cement is scaling. It bubbles up; I scrape it and a white powder comes up. What can I put on it to stop the white powder from coming back and to make the paint stick to the floor?
A. By the cement scaling, do you mean that it is breaking up or simply that the white powder is developing? The white powder is undoubtedly efflorescence. Moisture is dissolving the salts in the concrete and bringing them up. The moisture then evaporates, leaving the salts behind. It sounds to me that after 44 years you are suddenly having a mild moisture problem at the base of the walls — just enough to cause this new problem.
Check the grade around the house to see if there have been any changes that lead the water from the roof or gutters to pool against the foundation. If you find any anomalies, take care of them, and see if that solves your problem.
Attic fan causes moisture on basement ceiling
Q. My neighbor has an attic fan with the thermostat set at 85 degrees F. He was forced to shut the fan off because it created a great deal of moisture on the ceiling in the basement of his house. What is the problem?
A. It sounds as if there is a louver in the ceiling of the top floor of the house. The attic fan sucks air from the house and depressurizes it. Outside air is sucked in through whatever avenues it can find and, if there is not enough supply air through openings on the lived-in floors because windows are kept closed, outside air may be drawn through openings in the basement. Warm, moist air will condense on any cooler surfaces.
Venting foundation could worsen moisture problem
Q. I have a California ranch with a full basement with half of it finished; the other half is part garage/storage (the house is built into a hill, the back is at grade, the front is underground).
I run a dehumidifier in both areas and it controls the moisture level well but I was wondering if I put a vent in the foundation would it remove some of the moisture or make the problem worse? I also have windows in the finished area and was wondering the same: Would opening the windows help or hurt? Right now I keep them closed and just run the dehumidifiers.
A. In the humid part of summer, all basement windows should be kept closed and dehumidifiers should be kept running. Open the windows only on cool, breezy, dry days if you wish, otherwise all the wood components of the framing and other items stored in the basement will absorb the moisture in the air. This often leads to mildew.
Q. Three years ago, we moved into an end unit of a semi-attached ground-floor ranch-type condominium built on a concrete slab.
A year ago, we began to notice that the wall-to-wall carpeting was developing a dirty stripe along the outside walls and now, mold is beginning to grow also.
Cleaning the carpeting has not helped for long; the dirty stripe and mold return.
The rug people tell us that the reason for this is that our building does not have a vapor seal on the concrete slab whereas later units in our development have it because the building code was changed to require it.
The siding is aluminum. Is this condition due to moisture coming in at the bottom of the walls? What can be done to eliminate this problem?
A. It does, indeed, appear that there is no sill sealer under the outside wall plates. Cold air and moisture are infiltrating at these points and the carpeting gets damp and collects dirt; it becomes a perfect breeding ground for mold.
At this point, the only practical solution is to remove the bottom aluminum siding panel and thoroughly caulk the joint of the wall plate with the concrete slab before replacing the panel. The carpeting should also be pulled up along the edges of the outside walls and the same joint caulked as well. This should stop air infiltration and resolve your problem.
If it does not, the exterior edge of the concrete slab should be insulated with 1-inch rigid extruded polystyrene. The insulation should be covered with ½-inch pressure-treated plywood and both the top of the plywood and the insulation will have to be flashed to the siding.
Mobile home is damp underneath
Q. I purchased a double-wide mobile home on 1/4 acre that’s very wet. The home has skirting. I removed some and determined that it’s damp underneath most of the time. Will I have a problem in the future? What should I do?
A. You didn’t tell me where you are located. I am assuming that you do have a concrete pad under the home as is customary.
If you are in a cold climate, remove as much of the skirting as practicable in the warmer weather to let the underneath of your home dry up but you will need to put the skirting back before freezing weather comes along. If you live in a moderate to warm climate where freezing in not a problem, you can substitute a number of the existing skirting panels with ventilated skirting year-around.
Because the concrete pad was probably poured over soil without attention to good drainage, try covering it with 6-mil plastic, fitting it as well as you can around the piers and any other protrusions through the concrete; tape these joints with duct tape. Hold the plastic in place where it meets the skirting track with bricks or stones every few feet.
This should help control moisture from the soil through the concrete, which is a somewhat porous material.
Insulating a wet crawl space
Q. The old part of my ranch house has a four-foot crawl space. I have had installed automatic louvered vents that purportedly close when it is cold and open when it is hot. There is no insulation in the “ceiling” of the crawlspace.
I put an addition on, which also has a four-foot crawl space with non-automatic vents. The contractor insulated the “ceiling” of the crawlspace. The house is heated and cooled with forced hot air by way of ductwork in the crawlspaces. However, during the hot summer months with the A/C on, the insulation gets very wet with condensation.
I’ve heard conflicting theories. Some say that if a crawl space is vented, you should not have insulation. Others say insulation is good. I do not think that the condensation is a good thing. Should the insulation stay or go?
A. Recommendations for the treatment of crawl spaces have dramatically changed in the last 20 years or so. Most building codes still specify ventilation although it has proved to be the wrong thing to do. The best strategy for crawl spaces is to thoroughly cover the bare ground with 6-mil plastic.
If the crawl space leaks, fix any grade problems outside to keep water away from the foundation, but bring the plastic up the walls to a point a few inches higher than the outside grade and tape it to the walls. Make sure that the plastic applied to the walls is under any plastic you will need to add on the soil (if the wall plastic is on top, any water will flow right over the floor plastic.)
Close the vents permanently: venting a crawl space in winter makes the floor above cold and in summer, it introduces huge amounts of moisture in a cool space. This is probably responsible for the condensation you have experienced if you live in a moderate to warm climate.
It is best to insulate the walls of the crawl space with extruded polystyrene rigid insulation. Don’t forget to insulate the band joists as well. This will condition the crawl space, which now robs a lot of heat from the ducts in winter and increases the loads on the air-conditioning in summer.
Crawl-space insulation falling down, moisture building
Q. We live in a home with a crawl space that is only about two feet tall. The insulation has all fallen down and sometimes we have a small area with a little water. We live just 3 blocks from the ocean and want to know what kind of insulation would be best for this situation.
We also have a lot of condensation in the attic. The plywood is wet and the nails drip water. Do you recommend a ridge vent? I would appreciate any advice you can give me as we are new to this area and don’t know what to do. Thank you.
A. I assume that the crawl-space soil is bare and not covered with a 6-mil plastic vapor retarder. This is likely to be responsible in great part for the attic’s problem. It is also likely to be responsible for the insulation falling out between the floor joists; the paper vapor retarder holding it up may have rotted away.
I suggest you remove all the insulation batts. If they are in good shape and not soaking wet, and the paper vapor retarder is still sound, use them to insulate the walls of the crawl space. If they are wet and the paper is rotten, put them in heavy contractors trash bags and throw them away.
The first thing to do is to cover the crawl space floor with 6-mil plastic being careful to bring the plastic up the walls to the outside grade level. Since you have had some water seepage, install the plastic on the walls first by stapling it to the mudsill onto which the floor joists rest. Be sure that this plastic is wide enough to cover as much of the soil as possible.
Next, put another sheet of plastic on the ground from wall to wall, overlapping the plastic that is covering the walls as much as possible. This will prevent water from seeping onto the plastic where it cannot be absorbed by the soil. If the fiberglass batts are usable, staple one of their ends to the mudsill and let them hang down to the floor, bending them to cover the floor by a foot. Place bricks, stones or whatever you can find (except untreated wood) on the flat part of the batts against the walls to hold the insulation tightly. Use a stapler to staple the flanges of adjacent batts together.
But if the fiberglass batts are not useable, adhere 1-inch thick extruded polystyrene rigid insulation (blue, grey, pink or green, but no white expanded polystyrene beadboard) to the walls after cleaning them with a stiff brush. Apply daubs of StyroBond or polyurethane caulking to the concrete and press the insulation boards into the adhesive. Then staple plastic to the mudsill, covering the insulation following the instructions above.
Now check the grade outside and make sure it slopes away from the foundation.
Next, check for any convective paths from the living quarters into the attic and seal them up. If you can do the crawl space work and take care of any convection over the winter, wait to see what happens to the attic next winter after it has had a chance to dry over the summer. If you find new condensation, then more investigation will be needed to determine the best methods to ventilate the attic.
Sill over crawl space stays wet
Q. The wood sill on top of my crawl space foundation is soaking wet. Yet a similar sill in the basement is dry. A year ago we installed 9-inch fiberglass insulation with the vapor barrier facing the heated side between the crawl space joists. The ground in the crawl space is hard and dry. Yet even with the dry summer last year, the sill remained so wet I can run my finger over it and push water ahead of it.
A. Obviously, even though the ground is hard and feels dry, there is still considerable moisture exuding from the soil. With the conditions you describe, you risk rot on the sill and floor joists, particularly now that they are covered with insulation, which reduces their drying potential. A bare dirt crawl space needs a great deal of ventilation, which you don’t mention having.
The simplest thing to do in your case is to remove any debris or sharp objects from the crawl space floor. Lay 6-mil plastic all over the floor. Weigh it down at the perimeter with stones or bricks. Do the same around the piers. Where you need to overlap plastic, do so by at least 2 feet.
After the plastic has been down for a week or so, check to see if moisture is beading on its underside. That’s your clue that you have found the source of the moisture on the sill. But if there are no water beads, pull down a piece of the insulation between the floor joists and see if the area is dry. If not, you have another problem and I’ll need more information about the set-up to be able to help. For instance, are there vents in the crawl space foundation, and are they always open? If so, close them permanently once the dirt floor is fully covered with plastic—they are not needed and cause problems.
You may want to place a dehumidifier as near the center of the crawl space as you can with the air intake facing the access door to the crawl space and the discharge away. Connect a garden hose to the discharge tube and have it empty into a large container in the basement for ease of handling, and run it for as long as necessary to dry the crawl space.
Grading when back yard slopes toward house
Q. My back yard slopes down toward the house and, when it rains or the snow melts, water runs down my basement. I would like to install drain tiles on the back and side lot line and lead them past the house. Which kind are recommended and should they be covered?
A. You don’t need drain tiles if you are only dealing with surface water. And it is best to handle the water closer to the house than the back lot line; otherwise you still will have the problem from water coming between it and the house. Have a contractor with a small machine like a Bobcat create a gentle swale a few feet from the rear of the house and continuing as needed to the side where it can lead water past the house.
The grade should slope from the house to the swale. This will require making the grade from the swale to the rear lot line steeper unless you opt for a retaining wall on the outside of the swale. You could, then, use the extra dirt to flatten the back yard in back of the wall, making it more useful. Access to it can be created with steps and a flower bed can be made at the base and the top of the wall.
Grading when a house is between two hills
Q. Our 1863 house is situated between two hills, both steep. Water drains into the basement like crazy, and about a year ago the ancient mortar breached in one place, and the water gushed in like an open faucet. We have a sump pump but, because the floor is level, we have to push the water toward the pump with a snow shovel.
My mother had the side of the house dug up and preventive measures taken twice (I’m not sure what was done, as I lived elsewhere at that time), but that was maybe 20 years ago. A neighbor solved her problem by having an inner wall built up against the old fieldstone wall. It cants up, being wider at the bottom. It seemed to solve her problem in that area, although it’s damp in other areas.
My handyman seems to think it would be better to dig yet again on the outside rather than to build the interior retaining wall, as he feels the water pressure would breech the second wall as well. I really hate to get into digging! What is your excellent advice?
A. As proven over time, the digging and whatever else was done (twice) 20 years ago has not solved the problem. With the type of fieldstone foundation you have, it may be possible—but difficult—to waterproof it from outside. You would do this using plastic sheeting and backfilling with coarse material that would allow water to percolate to an outside perimeter drain, but the drain needs to be able to discharge water to daylight somewhere to be useful. If this is not possible, the work would be in vain.
The simplest way to deal with the problem, if it is at all possible, is to raise the grade against the foundation so it slopes away at least 2 inches per horizontal foot for as far away as possible (4 to 6 feet is ideal). This would prevent water from the two hills from reaching the foundation. Plant a healthy stand of grass on the raised grade.
If this solution is not possible, creating swales a few feet from the house to direct water to a natural outflow can also work. Or, a French drain can be built at the base of the two hills. It would consist of a trench a few feet deep with a perforated pipe at the bottom and the rest of the trench filled with stones to capture the water as it runs down from the two hills. That will also require a daylight outlet. The house side of the trench should be lined with plastic to keep the water that fills the trench from percolating toward the house.
These are all suggestions that may or may not be practical; it’s difficult for me to say without seeing the lay of the land. An expensive alternative would be to have a waterproofing contractor install a fiberglass gutter at the base of the walls leading to the sump pump, which, I assume, discharges outside to an area where the water can flow downhill and not be re-circulated into the basement.
Raising the grade when siding is close to the ground
Q. The earth against our two-year-old foundation has settled. As a result, water is running against the house and the basement leaks. Unfortunately, I can’t raise the grade too much as the wood siding is too close to the ground. The only solution I can see is to cover the bottom siding board with aluminum flashing and raise the grade against it. Is this a sound solution?
A. No, it isn’t. Although there are no termites in your area (Northern New England), there are carpenter ants, which may delight in the damp environment you will be providing them with. Soil dampness is bound to permeate the area behind the flashing. There are other ways to solve the grading problem.
If there is enough of an overhang to discharge roof water safely away, you can set pressure-treated 6×6-inch logs about 3 inches away from the siding so as to leave an air pocket; you’ll have to constantly remove all debris and leaves that will accumulate in it. Raise the grade against the logs.
Or, remove the bottom siding boards, treat the sheathing with Cuprenol Wood Preserver Green or equivalent wood preservative, and apply an ice and water guard membrane to a height of about 8 inches above the final grade. Install a Z-flashing under the last siding boards and cover the membrane with pressure-treated plywood set under the flashing.
Or create a swale a few feet away from the house, sloping the grade from the foundation to the low point of the swale. If you can lead the swale to lower ground, so much the better but, if not, at least the water is kept away from the house.
Replacing backfill next to concrete-block foundation
Q. I have a problem with the basement wall on the higher-grade side of my house. The wall is built of 11 courses of cement blocks and was backfilled with the native red clay and other soil when the house was built 48 years ago. I suspect I was in a hurry when I built the house so now I have to redo the backfill. The basement wall has not moved much but the hairline crack in the mortar joint indicates that the wall is moving.
I need to know the proper fill material to use and the proper way to grade the soil to prevent a future problem. The wall is 36 feet long and the house is a one-story brick ranch. I don’t see any cracks in the mortar joints of the bricks yet. I would appreciate your views on this situation.
A. If you only see a hairline crack in a 48-year-old concrete block foundation, I wonder why you would want to go to the trouble and expense of excavating the affected wall and redoing the backfill. Keep in mind that there are some risks involved in removing the existing soil next to the foundation; it will take an operator who is very experienced with the use of a backhoe, as well as some hand shoveling. At this point, I would suggest that you simply make sure that the grade slopes away from the wall in question at the rate of about 2 inches per horizontal foot and plant a healthy stand of grass on it to control the travel of water.
However, if you want to replace the existing backfill, have the soil excavated to the base of the footings. On the side of the excavation away from the house, pin a sheet of geotextile fabric wide enough to start at the bottom of the trench and eventually cover the stone bed you will install. Spread a couple of inches of egg-sized crushed stones at the bottom of the excavation.
Lay a 4-inch perforated drainpipe on top of the stone bed and, at the lowest point in the grade around your house, connect it to a solid drainpipe leading to daylight, since your land slopes. Add a minimum of 1 foot of the same crushed stone (more if you can) over the perforated drain pipe. Fold the fabric to cover the stones. Continue the backfilling with coarse sand or bank-run gravel to within one foot of the top of the excavation and complete the backfilling with native soil sloping about 2 inches per foot. Plant grass on it; avoid shrubs or trees.
Protection from an underground stream
Q. The house I am buying is under construction. The basement is built of 8-inch-thick blocks coated with cement and black bitumen.
There is a small underground stream about 4 feet below grade. The contractor has had to use a pump to keep water out of the trench so construction could proceed.
A. The builder needs to lay a crushed stone bed at least a foot thick at the outside base of the foundation and bury a 4-inch perforated drain pipe in it. The stones must be covered with geotextile fabric and coarse material used to backfill up to a foot from the final grade. Native soil completes the backfill.
The drain pipe must either run to daylight at a spot downhill from the house, be connected to a sump (low spot) equipped with a submersible pump inside the basement, or be connected to the local storm sewer if the local authorities allow it.
Q. When we built our house four years ago, we had a vegetable cellar built under the front stoop. It has a cement floor, block walls, cement roof and two round holes on each side for ventilation. When it rains, big water drops form on the ceiling and drip down, and the block walls are also wet. We applied a sealer on the cement stoop, and the ceiling and walls of the cellar.
After the first rain, the sealer started to come off, and we are back to where we started. In winter, big drops also form on the ceiling from condensation. What can we do to make the cellar usable?
A. You did not mention what kind of sealer you put on the concrete stoop; the right kind should have worked and made it waterproof. Trouble is, what you put on may prevent the adhesion of a more effective product; it may have to be removed.
Clean the stoop floor and apply Thompson’s Water Seal or a mixture of equal parts of boiled linseed oil and mineral spirits every year to repel most of the rain water. Paint the exterior walls of the stoop with two coats of a waterproofing product such as Thoroseal and do the same to the interior walls and the ceiling of the cellar. This should keep the water out. For Thoroseal to bond properly, you’ll have to remove whatever you put on the surfaces first; they must be clean.
To prevent winter condensation on the ceiling, apply extruded polystyrene such as Styrofoam or FoamulaR to the ceiling with a compatible adhesive such as Styrobond. If condensation is also a problem on the walls, do the same. You’ll have enough cold air coming through the four ventilation holes to keep the cellar cool.
Testing a sump pump
Q. We’ve recently moved into a new house equipped with a sump pump. Since I’ve never had any experience with these, I wonder how reliable they are. Do I have to wait until the basement floods to find out if it works?
A. First, let’s hope that your builder installed it as a precaution and that you won’t need it. But it’s easy to check if it functions properly. Pour water in the sump until the float of the pump kicks it in, and watch it remove the water.
Replacing sump pump with drain pipe?
Q. I have a basement sump pump that operates during heavy prolonged rains. I have a steep slope in the front of my house and was wondering if a straight 4? PVC open-ended gravity drain pipe would be just as effective and more reliable.
I would start the pipe close to the foundation (below the elevation of the basement floor) and slope it underground away from the house for about 30 feet. Would it have to originate near the existing sump, or would any location along the foundation drain away any rising groundwater?
A. The fact that you have a sump pump that operates during heavy rains tells me that if there is a drain on the exterior of your foundation, it may be clogged and not functioning. Or it may be that there is no foundation drain. In either case, the pipe you propose to install may not be very effective.
However, if there is a functioning drain, where does it discharge now? It would be unusual for a builder to direct the discharge of an exterior drainpipe to a sump pump when there is a slope that would permit a daylight discharge. So there may be an existing drainpipe to daylight that became clogged over time. You may want to look for it on the slope. If your research fails to find an existing daylight drainpipe or you know that there is no foundation drain (or assume that it is clogged), you may want to try your idea of installing a pipe from the nearest corner of the house to the discharge point that you select.
If you do, I suggest that you follow these steps: dig out a 2-feet square and 2-feet deep area to form a pit at the base of the foundation with half of it below the footing, line its sides with geotextile fabric, fill it with egg-size stones, cover the stones with fabric and install the drain pipe at the bottom of the pit. This may work in catching water from a rising water table. I urge you not to get rid of the sump pump just in case the new pipe does not do the job or eventually silts up.
A final question to ask yourself: Is it really worth doing all this work and disturbing existing landscaping if the present system does the job?
Why have a sump?
Q. I have read your comments dealing with the best ways to prevent basement leakage from the outside. However, if this does not seem to be working, what else could I do?
Some companies guarantee to correct basement leakage from inside with a sump pump. Is this something you would recommend? Are they expensive? How do they work? Or should I have the outside dug up and something done to correct the problem?
A. If you have done all the things I have mentioned to correct the leakage from outside and the basement still leaks, you may be dealing with an underground water source.
If there is a layer of crushed stones several inches thick under the basement slab, the installation of a sump pump may solve your problem, as the sump should pick up the water before it gets above the slab. Install it near a wall in the best place to dispose of the water outside.
The best sump, in my opinion, is made by cutting a hole in the concrete slab 30 inches square. Dig down 30 inches and place 6 inches of crushed stones on the bottom of the excavation.
Next, put an 18×18-inch flue liner on the stone bed and fill the space between the liner and the excavation with crushed stones to the bottom of the existing slab. Mix concrete and fill the area around the liner with it.
Install a submersible pump in the sump hole; connect a plastic pipe of the proper diameter to it with a check valve where it connects to the pump. Go as high as you can with it and connect a horizontal pipe to it with a slight slant to the outside.
The pipe should discharge onto a splash block, and the grade should slope away so the water will not be recirculated down to the pump from outside.
A good-quality pump should run around $100. They work automatically when the water level in the sump hole triggers the float. Digging outside is expensive and disruptive and generally unnecessary.
Best way to install a sump pump
Q. Can you describe the correct procedure for installing sump pumps in a sump pit in the basement? What is the best location for a check valve? Attached to pump discharge or someplace in discharge pipe or tubing?
Should a 1/8- inch hole be drilled in the discharge line to prevent air lock? If yes, where should this hole be drilled in reference to the check valve? Instructions from different manufacturers vary; some say drill a hole, others never mention it.
A. The best pumps to use are the submersible kind. The best place for the check valve is just at the pump’s discharge. As for the hole, follow the pump’s manufacturer’s instructions.
Protecting basement from high water table
Q. My sump pump runs at least 11 months a year. If the power goes out, my basement floods. The land behind me is high and when it rains a lot in the spring, my neighbors’ back yard is a lake. Is there anything I can do about this problem?
A. From your description, it sounds as if you have a high water table or there is a lot of subsurface water coming down the hill. The solution may be a French drain (also called a curtain drain although there are differences between the two).
For either of these drains, a deep trench is dug at the base of the hill behind your house and is carried to one or both sides of the house until it can discharge to daylight. The side of the trench nearest the house is lined with 6-mil black plastic and the trench is filled with egg-sized crushed stones after a 4-inch perforated pipe has been laid a couple of inches above the bottom of the trench. The purpose is to intercept the subsurface water and lead it away from your basement.
Life-span of a sump pump
Q. The pedestal sump pump located in my basement is 15 years old. It looks it but it is working well. It is needed only when there are heavy rains or snow melts in the spring when it may run for ten consecutive days until the ground dries.
I am concerned that the pump will stop working during one of these extreme weather conditions. This would cause my basement to flood and perhaps put me in a situation where the stores are out of stock due to high demand or I can’t get it repaired.
What is the normal life expectancy of a 1/3-horsepower pedestal sump pump? Are there ways to assess its condition? Should I adhere to the credo that “If it ain’t broke, don’t fix it” or to the one that says “It is better to be safe than sorry”?
A. Electric motors that are properly maintained (lubricated if need be; check the instructions or look for oil cups) should last for a very long time. In the case of your sump pump, it is only working intermittently, which is a light load on the motor.
The more likely problem with a pedestal sump pump is that the blades in the foot of the pump may become frozen from the scum and scale in the water if the pump is idle for extended periods and the water is of poor quality. Your best insurance is to operate the pump once a month or so to keep it limber.
Sump pump comes on too often
Q. We live in a house in a nine-year-old subdivision. Our sump pump comes on every 15 to 20 minutes all day and night long regardless of the weather conditions. Is this normal? Should the pump be left on all the time year around? Our neighbors don’t have that problem.
A. You obviously have an underground water problem such as a high water table or a spring near or under the house. It’s the only explanation I can think of for a sump pump to run as yours does. The fact that your neighbors’ pumps don’t run as often may be because their houses are on a higher soil stratum (if a high water table is the problem), or it may indicate that a spring is more likely to be the cause of your particular situation.
If you stop the pump, one of two things may happen, depending on the cause: If you’re dealing with a high water table, the water level may not rise any higher than it is now and your basement may not flood, as I doubt that the pump can be instrumental in lowering the water table to the extent that it keeps your basement dry, but you won’t be sure until you try. In the case of a spring, it may be different, and the sump pump may prevent basement flooding that would occur if you stopped it, unless there is an outlet for the spring water equivalent to its volume.
As you can see, the answer is pretty muddy. Try shutting off the pump to see what happens. Stand by and watch to see if the water level rises significantly.
Relocating the discharge from a sump pump
Q. I have a sump pump in the basement of our circa-1900 farmhouse. The 1½-inch hose from the pump leads outside underneath a porch (which has about 8- to 10-inch ground clearance, so I can’t get under it) and empties onto the lawn. In the winter, the water in the hose freezes, making the pump nonfunctional until the next significant thaw. This is a problem I need to resolve. Any suggestions?
A. The best solution seems to be to relocate the discharge hose to another area of the wall, not under the porch, since you can’t get under there to slope the hose downward so that it drains completely each time the pump activates.
Channeling water to the sump
Q. There is water seepage along one of my basement walls at the floor line. It is about 15 feet from a sump. I know they make a product that can be laid at the joint of the floor and wall to channel the water. Where can I purchase it?
Also, I ran the 1½-inch pipe from the sump pump 150 feet away to a ditch. The pipe is buried at least 3 feet and covered with blueboard rigid insulation but the outlet is only 1½ feet from the bottom of the ditch. There is a good pitch to the pipe. What can I do to prevent freezing?
A. I don’t know where you can find such channels in small quantities and at a reasonable price but you can easily make up your own. Buy a piece of vinyl gutter that is shaped like a broad “U”; cut it in half lengthwise and place it upside down with the cut edge against the wall and its flat top edge against the floor.
Clean the floor area on which you will glue the gutter. Mark the outer line on the floor and remove the gutter section. Run a bead of flexible caulking such as polyurethane or use a waterproof construction adhesive inside the line you have drawn. Place the gutter back and press its flat top edge down into the adhesive.
If you prefer, you can accomplish the same thing with a piece of 2×4-inch pressure-treated lumber fastened to the floor in the same manner.
It is unlikely that the discharge pipe will freeze considering the precautions you took. The steep pitch will cause the water to discharge quickly and running water generates its own heat. But if you are concerned, why don’t you get a hay bale from a farmer or garden supply house and place it over the discharge outlet to insulate it for the winter. Remove it and store it safely until next winter.
Drafty basement in a historic house
Q. We live in an 1831 brick house with a stone foundation. We recently had an energy audit, because some parts of the house are very drafty. The auditor found that a lot of the cold is coming from the basement around the foundation. (I know this is true because I can hardly stand in front of my stove in the winter because there is such a draft coming from underneath.)
He suggested spraying some sort of insulating stuff all over the stones that would create walls with a relatively smooth appearance. I don’t know this product, but I’m concerned about whether that is a good approach in a historic house. How would you handle this? Most of the basement is pretty dry, though one wall can get wet in a heavy rain.
A. There are some serious concerns about spraying insulation on a historic stone-wall foundation. There is a great risk that insulating the foundation may cause frost to penetrate deeper and push the wall in.
Depending on the type of insulation, there is a concern about flammability, and in the case of foam insulation, off-gassing for an extended period of time, which can result in health problems.
In case of a fire in the basement, foam insulation emits poisonous gas, an obvious danger to the occupants and the fire responders. Therefore, if used, it should be covered with a fireproofing material. In some areas, building or fire codes may prohibit spraying on insulation in this manner.
A better solution to seal off air infiltration that is causing the drafts you feel is to ascertain the condition of the stone foundation, clean it if needed, and tuck-point it with an appropriate mortar. You should retain the services of a mason experienced in historic restoration, as using the wrong mortar can cause problems.
There may also be some air infiltration around the sills; these spaces can also be sealed with mortar or canned foam (which would represent much less of a fire danger, being such a small amount).
If you still feel some draft, you may want to consider stapling Tyvek to the bottom of the floor system. Do not use insulation or plastic, which may cause problems by trapping moisture within the floor system. Tyvek is vapor permeable, providing an air barrier without sealing in water.
As to the wall that gets wet, you should check the grade around the entire foundation (water can travel far). If it is possible to raise it to slope it away from the foundation, but still leave some of the foundation showing, consider adding some topsoil and maintaining a healthy stand of grass on it. Tuck-pointing this wall may not be too successful if there is a strong hydrostatic pressure on the wall, and the pressure could damage the wall.
If there is not enough of the foundation showing to raise the grade, a swale can be built from the foundation out a few feet with a positive outlet to move the water away and prevent it from percolating and leaking in the basement.
Topsoil used for slope away from foundation
Q. I need to build up the area around my foundation to slope runoff away from it. What type of material do you suggest: ground stone, sand, topsoil, etc?
A. Topsoil with a small amount of clay is best. Ground stone, sand and any other coarse material will allow water to percolate which defeats the purpose.
All you need is a slope of about two inches per horizontal foot. Plant and maintain a healthy stand of grass on this soil. Avoid shrubs and flowerbeds; keep them from six to eight feet away from the foundation in groupings you can enjoy from inside through your windows.
Shrubs may be main cause of water in basement
Q. I have had water in my basement three times in the 25 years I’ve lived in my house. Each time it has been late winter or early spring when the ground was frozen and heavy rain for two or three days occurred. No problems in summer, fall, etc.
The grade slopes downward to my foundation from the street, levels off and slopes upward to the top of the foundation wall. The grade also slopes downward on each side of the house and is level with the basement floor. Water only enters from the front of the foundation.
I propose to put in a curtain drain 6 to 8 feet from the front foundation (to avoid removing shrubs) to a depth of 6 to 7 feet, and run a drain to the lower grade. I believe water pressure builds up when the ground is frozen and forces the water into the basement.
The interior walls are paneled and I cannot tell where it comes in, but when it starts, it comes in fast. Do you believe this will cure the problem? I would hope the water would take the path of least resistance.
A. Considering the conditions you describe, I believe your problem is caused by the shrubs against the foundation. Flowerbeds and shrub beds are usually flat and somewhat irregular, even though you mention that the grade rises toward the foundation.
When the ground is frozen, any water falling on these beds will flow to the lowest points and run to wherever it can. The weakest point is the joint between the earth backfill and the foundation walls, as rainwater races down along the foundation and finds a way inside. This is consistent with what you describe.
A curtain drain will not solve this problem, as water running down from the street should follow the swale in front of your house and not reach your foundation. Save your money. The solution is to build the grade up so that the spring rainwater and melted snow cannot reach the foundation but flow toward the swale instead.
Checking for water trapped in basement cinderblocks
Q. I have a 1200-square-foot, one-level ranch home, 1955 vintage. When my wife and I bought the house twelve years ago, the basement was completely raw—poured concrete floor and cinderblock walls.
About seven years ago, I purchased some Sears moisture-proof basement paint and applied three coats to the basement walls and lapped it 6 inches onto the floor. Now, the basement is very comfortable, though we still run the dehumidifier three months of the year. I have carpeted most of the basement with low-pile industrial carpeting and a brown, wooly-looking pad. I also added a 12-foot by 12-foot section of ceramic tile in one corner under the washer/dryer. The ceiling is unfinished.
My concern is that I once read in your column that sealing concrete blocks is a bad idea because moisture can be trapped in the blocks and cause a mold problem. I would like to hire a professional to test for this and/or stick a little camera down in the block openings to have a peak and see if water is trapped in the blocks. Have you heard of any reputable companies that could do this type of evaluation? Do you have any other thoughts on this?
A. Checking the cinderblock cavities is something you should be able to do yourself. It is likely that the mudsill on top of the blocks, and onto which the floor joists rest, is only 2 inches by 4 inches, as was common in the ‘50s. The blocks are probably 8 inches wide (although, they should be 12 inches wide if the foundation is more than 5 feet below grade).
Using a stepladder, a mirror and a flashlight, check the cores of the blocks every few feet around the foundation. If you see any amount of water in any of them, it should be removed before it is likely to cause serious problems in the house.
This can only be done by drilling holes in the bottom of the vertical mortar joints of the base course using a masonry star drill and a hammer (or a cordless drill to avoid possible electrocution).
Insulating an older concrete-block foundation
Q. I have a mid 1950s ranch house with a block foundation. About two feet of the foundation is above grade. What is the best way to insulate it? I see my options as:
1.digging down about a foot or two and attaching rigid foam on the exterior,
2.rigid foam or fiberglass on the interior or
3.having liquid foam pumped into the blocks by drilling holes in the foundation.
Number 3 is what my parents had done in the mid 1970s to their house.
I get water in the basement during heavy rain storms a couple times a year along one wall. The water seems to come in at the base of the block wall and concrete floor. Don’t know if it matters but, I run a dehumidifier most of the summer too.
A. I vote for 2, using extruded rigid foam insulation (XPS). But you should address the leakage first. It is telling you that the ground against the foundation is saturated. This could result in frost pressure on the walls that could cause them to buckle. Examine carefully the grade against your foundation. Any low spot that can collect water should be raised so the grade slopes away from the foundation. If you have gutters, check that the downspouts discharge away from the house— often there is a low spot at the discharge point where water pools.
Once the leakage has been stopped, you can insulate the inside of the block walls but do not go any deeper than two feet below grade. (The greatest heat loss is above grade and the two feet below.) This will allow some heat to keep the frost at bay. Make sure the walls are clean and free of dust, etc. Apply daubs of Styrobond to the walls every foot in all directions and press 2-inch thick XPS (blue or pink) rigid insulation onto the adhesive.
Dehumidifiers are always a good idea in summer to keep the basement air as dry as possible and prevent mildew.
Dampness in lower level of raised ranch
Q. I live in a raised ranch house and am concerned about the dampness in the lower level during the summer. My son’s bedroom is on the lower level and he suffers from allergies. Short of air-conditioning, how can I alleviate the dampness? I do have a dehumidifier, but the upstairs windows are open. I am unable to close off the downstairs level, so I’m basically trying to dehumidify the great outdoors if I run it.
I know that the builder did not put in footing drains. The house is over 30 years old and the builder, so I hear, was not highly qualified. Does a lack of footing drains have any bearing? My house is heated in the winter with an oil furnace and a baseboard/hot water system and is plenty air tight. I would appreciate any guidance you can give me. I read your column regularly and enjoy it and learn from it.
A. The absence of footing drains should not affect the level of dampness you feel in the summer unless you suffer from leakage anytime it rains or when the snow melts. Lower-level dampness is usually due to warm, moist outside air getting in a cooler space such as the lower level of a raised ranch that is kept cooler because it is in contact with earth that takes a long time to warm up.
Air conditioning is one answer, albeit expensive to install and operate, but a high- capacity dehumidifier should also greatly help. I have a similar situation, having a two-story house with one side against a bank, and the dehumidifier keeps the lower level free of the smell of mildew.
Can you close the windows during the day while you are at work so the dehumidifier has a chance to catch up? And can you simply install some form of hanging curtain at the top or bottom of the stairs during the summer to isolate the lower level to some extent?
Stopping seepage through block walls
Q. There is a small amount of seepage through the foundation block walls in the front and rear of the house, which get the roof run-off. I think the concrete blocks were not coated underground. Once the walls dry up this summer, I plan on painting the inside walls with a waterproofing paint.
Would you suggest this or something else, and must I treat the exterior walls below grade first? The soil is very sandy.
How can I remove the white dust particles from the inside surfaces of the block walls? The block walls are now cracking. Are rain gutters a must?
A. I would advise you not to waterproof the inside of block walls. I have seen houses where this had been done in which the blocks were filled with water with very serious ill effects on the living quarters.
The fact that the walls have some cracks tells you that rain is allowed to percolate and freeze against the foundation, pushing the walls in. You need to top the sandy soil with loam with some clay in it, sloping away from the house and plant grass on it. This will move water away and may prevent further leakage. There should be no need to excavate and coat the walls; it’s a huge undertaking with questionable success.
Remove the efflorescence by brushing it off with a stiff bristle brush.
I am not in favor of gutters in cold climates where ice may build up in them and cause damage.
Radon testing
Q. We are getting ready to look for a smaller house this spring now that our children are gone. What is your opinion about radon testing, and what other advice can you give us?
A. It is a good idea to have any house tested for radon. But there are different ways of doing it.
First, to give you a good idea of the potential radon contamination of your house, the testing should be done when the house is going to be closed for an extended period of time and when there is a big difference between indoor and outdoor temperatures—that is, during the winter or the air-conditioning season. If you test your home for radon when it is warm outside, the reading is likely to be the same as it is outdoors because the windows will be open. There is nothing to be done about outdoor radon, and we have all been exposed to it from the day we were born, anyway.
As for the types of testing available, short-term testing can be done with charcoal canisters, but they test the radon level over only the preceding few days. I favor the longer-term alpha track system, which gives you readings over several months. This is the system I used at my house. I installed it in September and stopped the testing in March. Using this method, I was sure that I got a reading over a long period of time, through many temperature fluctuations and other variables.
When my clients ask me about the results of radon testing, I ask them: “Would you still buy the house if it showed a high reading?”
If your answer is no, then go for the quick-but-limited testing with charcoal canisters or with one of the fancy, expensive devices that gives instantaneous readings. Many inspectors carry them, but they charge an additional fee to use the equipment.
If the answer is yes, then buy the house and test for radon over the next heating season. If the reading is over the health limit set by the government, consider having mitigation measures done by experienced professionals.
More information on this subject, from the Environmental Protection Agency, can be found at http://tinyurl.com/qrgr4c.
Q. You have on several occasions mentioned an interior perimeter drain to solve basement water problems. We have such a problem and haven’t found a solution to date. Is this the solution for us? And what is it?
A. Most basement and crawl space water problems are caused by improper grading of the soil around the foundation and negative slopes on attached structures such as walks, patios, driveways, and stoops. A negative grade means that water is directed toward the foundation instead of away from it. Downspouts discharging roof water directly on the ground against the foundation instead of onto a splash block or an extension pipe or those connected to an underground drain pipe that has a break are also responsible for foundation leakage.
However, if all the conditions responsible for surface water problems have been corrected and there still is leakage, an underground water source is suspected. That is where an interior perimeter drain may be the answer.
This is often easier to provide and less expensive than excavating along the foundation to install or replace an outside footing drain. This, of course, depends on how extensive the landscaping is.
To build an interior drain, the concrete slab along the basement walls is removed in a band approximately a foot wide and the gravel and dirt excavated to the bottom of the footings. A couple of inches of new crushed stones are spread on the bottom of the excavation, a perforated drain pipe laid on top and more stones put over to the level of the bottom of the slab.
The stones are covered with plastic to keep the concrete from infiltrating them, a spacer in the form of an asphalt strip or pressure-treated board is placed against the wall, and the concrete is patched. The spacer allows water that may come through the walls to flow down to the perimeter drain.
The drain should terminate into a sump equipped with a good quality submersible pump discharging to the outside onto a splash block sloping away from the foundation so the water will not be recirculated.
Protection from underground water
Q. You have dealt with ways to handle wet basements caused by surface water. Would you now deal with underground water problems?
A. Although far less frequent than problems caused by surface water, there are nevertheless cases of foundation water problems caused by underground water sources. These can be a high seasonal water table (e.g., when snow melts in the spring or during very wet periods) or, for instance, water following an underground ledge.
First and foremost, houses with basements or crawl spaces should not be built under these conditions unless foolproof precautions are taken to handle the water.
In new construction this involves laying 8 to 12 inches of crushed stones, properly compacted, on the excavated area before pouring the footings, the foundation walls, and the basement slab. Depending on the amount of water, a network of perforated pipes around the inside of the footings and perhaps underneath the floor slab itself may be advisable in addition to the standard exterior perimeter drain.
The stones covering the exterior perimeter drain should be protected with one of the geotextile fabrics available today, and the drains should discharge to daylight downslope or, in the case of a flat lot, to a sump equipped with a pump inside the basement or crawl space. The sump should have a tight cover to reduce the chance of radon entering the house.
Curtain or French drains can also be very effective in intercepting water following earth strata down a hill. However, these trenches must be at least as deep as the footings of the buildings and have slightly sloping bottoms toward the discharge point or points.
A sheet of plastic is laid on the trench side closest to the building, 2 inches of egg-size crushed stones placed on the bottom, then a perforated pipe leading to daylight and more stones. Geotextile fabric is placed over the stones before backfilling with a layer of coarse sand and natural soil.
The difference between a curtain and a French drain is that a curtain drain is not filled with stones to the top whereas a French drain is, thus having the ability to catch surface water as well.
Mold, Mildew, and Musty Smells
Mold can be, at best, an annoyance, and, at worst, a dangerous allergen and a sign of rot that can cause severe damage. Even the relatively normal dampness that can occur in a basement can cause problems, particularly if the basement is used as living space or storage.
Q. Our basement is built of poured concrete walls and floor. It is dry. Will painting the walls cut down on the use of our dehumidifier? Should we use a concrete sealer on the floor?
A. You need a dehumidifier in a basement in the summer to remove excessive vapor in the air that causes musty odors and could lead to mildew formation on all surfaces. This is because the warmer exterior air already contains a high level of humidity and, when it is cooled by the concrete surfaces that reflect the temperature of the soil in contact with them, its relative humidity is considerably increased to the point where condensation occurs on these surfaces. Only dehumidification can control this problem.
This situation, prevalent throughout the warm and humid summer days, is the reason why I do not recommend leaving windows and vents open in basements and crawl spaces until we get dry, breezy and cooler days.
There should be no need to apply a sealer on the concrete floor unless there is a considerable amount of dusting taking place. But that is a different subject.
Dehumidifiers needed in most basements
Q. We live in the woods and have a very deep (400+ foot) well. When the weather is hot and muggy, the cold water pipes in our basement are always dripping with condensation (our well water is quite cold) which not only can be a nuisance but for a period of time also contributes to a strong musty basement smell.
We have considered purchasing a dehumidifier on a few occasions but I wonder if this might just be simply analogous to trying to drain a swimming pool with a spoon (due to the heavy condensation continuously on the pipes during those weeks). What would be your recommendation?
A. Dehumidifiers are really necessary in most basements, even in houses with central air conditioning.
I do not recommend insulating cold water pipes in a basement as all it does is move the condensation to pipes that are hidden in walls where it can do damage that is not discovered until too late.
Basement moisture smells permeate house
Q. I am concerned about the mold/mildew and odor that is building up in my elderly parents’ home, which is built at the base of a rocky hill.
The house is about 150 years old, has a slate roof, an unfinished basement with a stone foundation and a cement floor, forced hot-air heat and aluminum storm windows over the original windows. The basement has always had a damp musty smell but now the odor has permeated the whole house, which they don’t seem to notice. Even the bed pillows on the second floor smell bad. Their clothes smell, and when I stay overnight, my clothes and my hair pick up the odor.
The only place where there is evidence of black mold buildup is on the gaskets of the freezer in the basement, and the refrigerator on the main floor, but I’m very concerned about the health implications, as well as the unpleasant smell. I should add that my parents’ home is tidy, and is cleaned regularly. What advice can you give?
A. Your parents should keep the basement windows closed all summer and use a dehumidifier. Open windows bring in a lot of warm, moisture-laden air in a cool environment. This raises the relative humidity and mildew and mold follow.
I assume that the basement does not leak since you do not mention it but it is not uncommon for old stone walls to admit moisture. If this is part of the problem, you may want to write again and we can discuss alternatives
Close windows when using dehumidifier
Q. My home was very old before we did it over 50 years ago. When we bought it there was a spring in the dirt cellars. It fed the pump in the kitchen sink. We dug the spring out, put in good drains, filled it in and applied a cement floor.
We have used a dehumidifier, placing it on the old cement laundry tubs into which it empties. Last summer, my electric bill was $60 to $70 more expensive than my ordinary bill. Have you any suggestions to help me lower my bill? The dehumidifier is only two years old.
The west wall has an outside ground level door and four small windows but because I cannot do stairs well, I cannot leave the door and windows open during the day and close them at night or when it rains.
A. It’s a good thing you keep the outside door and windows closed all the time. If they were open, they would admit a lot of humidity and make your dehumidifier work that much harder.
If your very old house has stone walls, it may be the reason why much humidity still gets into the cellars in spite of the concrete floor you put in. The fact that you also had a spring in the cellars indicates that water is close by; it may keep the ground around your foundation damp. You didn’t mention any leakage so the moisture may enter the cellars as vapor through the old stone foundation whether the stones are laid dry or mortared in as old mortar is very porous.
I don’t have enough information to advise you on how you can lower your electric bill except to suggest that, if your dehumidifier has a humidistat, you raise its setting so it won’t run as often.
Musty smell in basement despite French drain
Q. I had a French drain installed in my basement because of water coming in after a heavy rain. I had rugs on the basement floor and I removed them but I still have a musty, mildew smell there.
I’ve washed everything with hot soapy water and bleach but I still have the smell. What can I do to get rid of it?
A. In the summer, you should run a dehumidifier. Although it is not as effective in winter because the temperature is lower, you might give it a try anyway since you are having such a problem.
An alternative is to hang a number of Mil-Du Gas Plus bags in the basement. A 7-1/2 ounce bag will take care of 1,000 cubic feet. You should be able to get Mil-Du Gas Plus in marine or RV supply stores.
For immediate results, you may want to try spraying Nok-Out on all unfinished surfaces throughout the basement (if there are any finished surfaces, you may want to try spraying Nok-Out on an inconspicuous area to make sure it will not damage them). Nok-Out can be ordered online at www.nokout.com.
Another choice is Neutron’s Autoscents dispensers, which deliver the scent of your choice over a long period of time (888-712-7127) or www.neutronindustries.com.
Musty smell coming from crawl space
Q. I have a crawl space under my living room, dining room and kitchen. Under the kitchen there is a dirt floor, the rest has a cement floor. We run the fan all year long to push the air. In the winter we have a humidifier; in the summer, mostly conditioned air.
There is a musty smell all the time. There is a very small seepage onto the cement in the crawl space under the living room—not much. There is a sump pump under there in case of any aggressive water seepage. What is the best way to get rid of, or control, the musty smell? I’m not sure if it’s coming from the cement area or the dirt area. It’s just always there.
A. I assume that when you say you are running the fan all year long, you mean the heating system’s fan; if not, I am missing something.
Try this and see if it solves the musty smell: Cover the dirt floor of the area under the kitchen with 6-mil plastic, making sure you bring it up the foundation walls by a few inches. Tape it to the walls just enough to hold the plastic up. Use as few seams as possible and overlap the plastic by a couple of feet where you need to join pieces.
Get a dehumidifier with a large capacity and a humidistat so it only runs when you need it and run it all summer long. Also try not using your humidifier in winter until the situation is resolved.
Since you have some seepage on the concrete, you should check the grade around the house for any flat or low spots, which allow surface water to percolate deeply and enter the crawlspace when it finds a weak spot.
Reducing basement moisture—what works and what won’t
Q. The basement of our 60+ year-old house is currently mostly dry, but only through the daily, year-round hard work of a dehumidifier and sump pump. We believe we have high groundwater.
The walls are bare concrete block and do not appear to have been treated in any other way than to have been painted on the inside. The paint has come off only in one small square in the SW corner. The floor is a thin slab of concrete with some cracks in it.
There is also a mysterious small hole in the slab on the north side that may be functioning as some sort of below-floor drain to the sump pump on the south side. The sump pump usually comes on a few times a day for a few seconds each time.
Occasionally we do get some water on the floor during heavy rains or if the sump pump fails for a few days, but usually there is no visible water. The ceiling is insulated with R-19 fiberglass batting because of stapled-up radiant heat installed under the first floor hardwood floors. We would like to make our basement less damp, mostly because of the high energy costs (we estimate $30-50/mo in electricity). However, our budget for doing this is tiny. I have 4 questions for you:
First, I am planning to get rid of the mold myself using a borax solution (I have a small child and am concerned about indoor air quality in our pretty tight house). Mostly, I can only see a little bit of it (black) around the bottom blocks of the wall on the north side. However, there is also some in the drywall beneath the stairs that go down to the basement. I have read about a non-toxic sounding product called Caliwel. Would you recommend using borax on the block walls and encasing the drywall using Caliwel?
Next, we discussed several options for making the basement less damp with a structural engineer. He recommended putting down Stego Wrap + concrete up to ground level. (We are never going to finish the basement and so probably wouldn’t dig up the slab–just have a slightly low-ceilinged basement.) However, he said if we don’t have too much hydrostatic pressure it might be possible to get away with just applying epoxy. Do you ever recommend epoxy for fixing a damp basement and if so, is there a good brand? We also looked into something called SaniTread–I believe it was rubber rather than epoxy–which appealed to me because of my concerns about offgassing etc.
If not, can you comment on the Stego Wrap + concrete over it option. A contractor told us he wouldn’t do that unless he were first installing a French drain, but I don’t remember the engineer mentioning that.
Finally, we have also considered insulating the basement walls with fireproof foam board to raise the temperature down there and therefore increase the amount of moisture the air can hold at 50% relative humidity. The native soil is supposed to be a silty loam and therefore the structural engineer recommended only doing so above ground level in order not to cause the foundation to fail. Would you recommend putting in the foam board? Throughout the recent cold snap the basement has been quite cool—at one point we measured the temperature at 43 degrees. Nothing has frozen however.
A. Since the concrete block walls are painted and paint is only peeling in a small area, it would indicate that the leakage is not through the walls themselves. It also seems as if the water is mostly coming through the floor and not much, if at all, at the joints of the walls and floor since the sump pump is able to take care of it except in exceptional circumstances. If water were coming in at the joints of the walls and floor, you would probably see it more often than you indicate.
It is also important to know that hydrostatic pressure is hard to resist and to control by trying to cap it. For instance, if leakage occurs at the joints of walls and floor, adding a membrane on the old concrete and covering it with new concrete may not do anything. There are other ways to deal with the problem.
But it is also important to understand that grade problems may be contributing to the leakage by allowing deep penetration from surface water(and perhaps roof water, if you do not have gutters) to overload the capacity of the soil to contain it and of the pump to handle it.
Check grade around foundation first
So the first thing that you should do is to check the grade around the foundation, as most foundation leakage problems are caused by flat or negative grade, low spots, mulched beds, hollows created by the discharge from downspouts or dogs looking for cool soil; driveways, patios, walks that direct water toward the foundation. Any such contributors to leakage should be corrected, including possibly expensive work to change the slope of masonry or asphalt elements.
Once this is done, if leakage persists, you may either have a rising water table following heavy or long rainy periods or snow melt, or an underground spring that swells from these occurrences.
Controlling the water table
The control of a seasonal water table or swelling spring may be done in one of several ways depending on where the leakage occurs. If the water comes through the floor, there may not be a sufficiently thick stone bed to act as storage while the sump pump is trying to discharge it. It is likely to be the case in a 60-year-old house with a thin and cracked concrete slab.
It is also essential to know that the water discharged by the pump is disposed of properly. Often, the discharged water is recirculated back to the basement because of grade problems that do not move it away from the foundation.
I am not clear about your comment that the structural engineer suggests using “Stego Wrap plus concrete up to ground level.” It can’t mean filling the basement with concrete to grade.
A membrane covered with a new 3-inch slab may repair the thin and cracked slab, and contain the water coming through the floor, but would the hydrostatic pressure force the water out to the perimeter where it would show up again?
Exploring underlying conditions
It may be worth exploring the underlying conditions by cutting a small area of the concrete to determine the thickness of a stone bed, if there is one at all. One possible solution is to break the existing slab into small pieces and use it as a stone bed. It may be necessary to add some stone to obtain a bed 4- to 6-inches thick. The stones should be covered with a vapor retarder, which can be the Stego Wrap or just heavy plastic. To ensure the proper curing and finishing of the concrete, the industry recommends that a 2-inch thick absorbing bed (coarse sand, crusher run, etc.) be spread over the plastic to absorb the extra water in the pour. The new slab should be at least 3-inches thick and should have at least wire mesh reinforcement. It should also have control joints every eight feet to prevent irregular drying cracks.
Removing mold
You may also want to consider removing the mold with an environmentally-sound oxygen bleach such as Oxy-Boost (www.ecogeeks.com.)
Painting the thin floor with epoxy does not sound like a worthwhile thing to do. All the cracks would have to be repaired and the old concrete may not be able to hold the paint against the vapor drive from the soil through the slab.
Although I have no personal experience using Caliwel coatings, it sounds like a good product to use on the drywall, as its anti microbial agents are claimed to kill bacteria causing the growth of mold. You could also use it on the block walls.
Draining, if necessary
I would be leery about using SaniTred as a way to waterproof the basement floor. I question its ability to withstand hydrostatic pressure, and would be concerned about mold growing under it.
The contractor who said that he would not use Stego Wrap and concrete has the same concern I have about hydrostatic pressure pushing water up at the perimeter of the slab. Installing a subslab drain leading to the sump pump is good insurance and advice. The drain can be installed around the perimeter of the basement when the present slab is broken into small pieces to improve the storage and drainage ability of the substrate.
Insulating a basement
The consensus among building practitioners is that, if you do not know the composition of the backfill around your foundation or you know that it is heavy native soil, you can safely insulate basement walls from the ceiling joists to three feet down below grade. If the backfill was done with coarse, well-draining material and you have a functioning foundation drainage system, you can insulate all the way to the slab.
Fireproof board insulation is fine, but it is really only fire-resistant and more likely made with fiberglass and not foam. But you can use flammable rigid foam insulation as long as it is covered with fire-resistant material such as drywall.
Waterproofing compounds basement-moisture damage
Q. The house I bought a few months ago has severe water damage in the basement; the block I live on is sloped and the house next door has about a three-foot elevation above mine, so it appears that the ground water level under my house is higher than all the houses up-slope. As a result, water has been seeping through all of the foundation’s cinder blocks on the up-slope side of my house.
The previous owner applied a black adhesive substance and pasted black tar paper from the inside of the basement. The cinder blocks are flaking and there are areas with a white powdery substance bulging on just about every cinder block on that side of the house, not to mention the mold and mildew that exist. In addition, someone apparently dug a trench about 18 inches wide around the periphery of the basement and filled it with concrete. Water is seeping through that too, and even after several hot sunny days that area remains damp.
There is a sump pump which is located at the down-slope side of the house; it only seems to work during extremely heavy downpours and does not seem to be of any use for the underground water that follows a heavy rain. That water appears to be what is seeping through the foundation only at the up-slope of the basement.
If you can offer any suggestions on how I can remedy this situation, I will be most grateful.
A. The previous owner made a mistake in attempting to waterproof the cinderblocks from inside. All it accomplishes is to allow water to accumulate in the cores of the cinderblocks from where it evaporates inside the house, potentially causing serious problems. It is probably impossible for you to remove the tar paper and the tar that was applied on the blocks.
The concrete-filled trench on the perimeter of the floor is likely an attempt to direct water to the sump pump through a perforated pipe buried below the floor. Obviously, this is no longer working.
The first thing to determine is whether the leakage is caused by surface water running down the slope from your higher neighbors or by underground water from a rising water table or a spring that swells in heavy downpours or long-lasting rain.
Leakage from surface water generally occurs quite soon after the heavy rain starts, whereas a long delay—sometimes of several days—is likely from underground water.
You should first check the grade around the foundation and make sure that it slopes away from it, especially on the up-side. If that solves the problem, you are done.
However, in the case of an underground water problem, you can have the up-slope-side wall excavated and waterproofed from the outside, but to be successful this will also require that at least one of the side walls be excavated as well, and that a drain pipe be installed on the back and side of your sloping yard to a storm sewer, if there is one, or to daylight. Or you can have a curtain drain built between your house and the upside neighbor. A deep trench is excavated to the depth of your foundation and carried to one or both sides of your house. Black plastic is pinned to the side of the trench closest to your house.
Two inches of egg-size stones are laid on the bottom of the trench followed by a perforated plastic pipe that runs to daylight. The backfill is done with the same size stones, either to the top (a French drain), which will also catch surface water or to within a foot of the top. Landscape fabric tops the stones and top soil completes the job. This may cause a problem with your down-slope neighbors if the water adds to what they already have.
Another option is to have a basement waterproofing company drill holes in the bottom row of blocks and install a fiberglass gutter system that leads to the sump pump. If the pump is not sufficient, you may need to replace it with a submersible pump of higher capacity. Whatever system you choose will be expensive.
The white powder is efflorescence and it can be wire-brushed off.
Odors and mold in a damp basement
Q. We live in a 100-year-old house and have a problem with a damp and smelly basement. It is mostly poured concrete but there are areas of dirt (I think our cat has been using that instead of his litter box!). What can we do to eliminate the odor? Any special products that you recommend for strong odor removal?
We also have a mold problem because of the dampness. Any recommended products for this? Are there local consultants out there that we should hire?
A. To eliminate any bad odors, try spraying Nok-Out on all unfinished surfaces throughout the basement (if there are any finished surfaces, you should try spraying Nok-Out on an inconspicuous area to make sure it will not damage them). Nok-Out is available online at www.nokout.com.
Where is the mold? One way to remove mold, if it is not too extensive and only on the surface, is to wash it off with a solution made of equal parts Clorox bleach and water. But if the mold is deep into the material and extensive, it is safer to have an environmental engineer take samples and recommend how to take care of it.
To reduce or eliminate the dampness, you should run a dehumidifier in the summer. An alternative is to hang a number of Mil-Du Gas Plus bags in the basement. A 7-1/2 ounce bag will take care of 1,000 cubic feet. You should be able to get Mil-Du Gas Plus in marine or RV supply stores.
Q. The basement walls of the house I recently bought were covered with black mildew. I have used a wire brush, sulfuric acid, and white paint, but the mildew is coming through.
I don’t know what else to use; I hope you can help.
A. You should have used sodium hypochlorite, not sulfuric acid. Mold and mildew spores, unless killed, will come through new paint coats.
Wash the walls with a solution made of equal parts of water and fresh Clorox bleach. Wear skin protection and old clothes and, very important, ventilate well by setting a fan blowing out in a basement window; open an opposite window. Rent a respirator labeled effective for chlorine.
Do not rinse; let the solution do its job and evaporate, but close the door to the basement and keep the ventilation going until all odor of chlorine is gone.
You haven’t mentioned it so I assume that your basement is not leaking but if the walls are built with cinder or concrete blocks, I would not recommend painting them with a waterproof coating.
Dark line around rug next to outside walls
Q. We have a house built on a cement slab about 4 to 6 inches above the ground at which point the vinyl siding starts. There is a dark line all around the edge of the rug that butts up against the outside walls. Is there a way to eliminate this problem? Vacuuming doesn’t cut it, and washing doesn’t seem to do much good either. Is it because the dirty air blows under the siding where it meets the slab and comes into the house with the dust? Someone told me that we cannot caulk under the siding where it meets the cement slab because it would cause mildew. Is that true? When they put the vinyl siding on five years ago, I watched them wrap the house with Tyvek first.
I hope you understand what I’m trying to tell you; my description might leave a lot to be desired. Could we caulk from the inside before we get the new carpeting so we don’t repeat the same process with the new rug where it gets dirty along the outside edges? Or can we caulk under the siding on the outside to keep this dirty air from entering, if indeed this is what is causing it?
A. Although it is possible that cold air is infiltrating at the joint of the concrete slab and wall framing, I think the most likely cause of the dark stain on the edges of the carpeting is due to the formation of mildew because the perimeter of the concrete is cold.
I see no reason why you can’t caulk the joint of the bottom plates of the walls and the concrete slab from both inside and out if there isn’t a sill sealer between them, as there should be. You should be able to tell if there is one by pulling the carpeting up along the edges and looking for it; it may be a black, shiny plastic covering cellulose; a strip of fiberglass insulation; a white or blue foam strip — or whatever is commonly used in your area. You can also check for air infiltration by holding the back of your hand or a lit candle as close as you can to the joint to see if you can feel cold air or see the flame flicker. Just be sure to pull the carpeting up and put something on the concrete to catch the drips from the candle.
If I am correct and the dark stains are caused by condensation and mildew formation because the slab is cold, the solution is to install rigid insulation against the outside of the slab. Dig down a couple of feet along the entire perimeter of the slab. Clean the concrete with a stiff brush, and water if needed; let it dry. Run a strip of polyurethane caulking or StyroBond at the top of the slab and put daubs of the same adhesive every few inches along the concrete all the way to the bottom of the excavation. Press in place a 1-inch thick rigid extruded polystyrene (Styrofoam blue board, pink Foamular or whatever is commonly used in your area).
Cover the insulation with half-inch thick pressure-treated plywood power-shot into the concrete or aluminum coil stock adhered with caulking or Styrobond, making sure that the insulation and its cover are properly flashed under the vinyl siding to keep water, dirt and other foreign objects from getting behind them. Backfill the trench, sloping the grade away from the slab and plant grass. An experienced carpenter should be able to do this easily.
Odors when house is closed for winter
Q. We own a house on a lake in New York State. It is approximately 60 years old and on an unmaintained road so it can be used only from May to October. Originally it was a one-story, two-bedroom house with a 6½-foot high basement.
We added a second story about six years ago. Our problem is an odor that comes from the basement and permeates the house once it is closed up. I have to bring all the linens, pillows, curtains, etc., back to New Jersey and store them until springtime.
The basement is built with cinder blocks. It is unfinished and it has a drain to get rid of water that enters the basement in the spring. There are two regular windows facing the lake and two doors to bring in furniture and other items for storage.
Our next-door neighbors’ house is situated the same as ours but their basement ceiling is higher and they do not experience the same damp smell as we do.
Would painting the cinder blocks help? Is there a kind of desiccant that we could use? We do run a dehumidifier during the months the house is used.
A. Do not paint the cinder blocks; it would not help and it may cause other problems.
You haven’t mentioned the basement floor. Is it bare dirt or concrete? If bare dirt, it should be covered to prevent moisture from the soil from evaporating into the basement and permeating throughout the house.
The problem is what to cover it with since you use the space for storage. The simplest way to cover bare soil is with 6-mil plastic, but it will not last if there is much foot traffic and moving of stuff around.
Concrete would be the answer but, since concrete is somewhat porous, it should be poured over a gravel base covered with 6-mil plastic. This would reduce the headroom unless the soil were dug out several inches.
If the basement floor is already covered with a concrete slab, unless it was poured as mentioned above, moisture can get through it. The only way to stop it is to paint the slab with epoxy paint after a thorough cleaning.
To reduce moisture infiltration, check the grade around the house and correct any deficiencies so water is directed away from the house and not toward it or allowed to stagnate on flat grade.
Use a desiccant such as MDG Mildew Control Bags and hang the bags in the basement and the house. You can buy it in RV and marine stores. Buy enough bags to take care of the cubic footage of the areas to be protected. The product lasts up to four to five months.
Mold spores and other allergens
Q. I live in a 20-year-old townhouse with a dry basement. A few years ago, I noticed a yellowish stain about 5 inches in diameter on the basement ceiling, near a window directly below a warm air register in the kitchen above it. I forgot all about it until yesterday. Although the stain has not enlarged, half of it had turned quite black, and I suspect that it could be mold or mildew.
My husband and I have been suffering from allergies to a number of things including molds. How can I get rid of mold spores and other allergens in our house? We currently use a 3M Micro Particle and Airborne Allergen Reduction Filter, which we replace every month. If there are professionals who can remove allergens inside our house, I am willing to spend money on it. We are really feeling very miserable.
A. There are such people and you can find them in your Yellow Pages under “Laboratories–Testing,” “Engineers–Environmental” and “Environmental & Ecological Products & Services.”
The stain you mention does appear to be caused by molds. Its change from a yellowish stain to a black one indicates it is active. There must be some moisture getting into the ceiling. The source should be found and eliminated.
It may be from some condensation in the duct (for whatever reason) or, more probably, from some leak from an appliance near the duct. The culprit may be the dishwasher. If this is not corrected, you will have a continuing problem. Most people are not allergic to a minor amount of mold spores but molds are always worth checking out.
Relatively few newer houses have cellars with dirt floors, but they’re a common feature in older ones, including fine historic homes. They can pose some maintenance issues that differ, at least slightly, from those of other foundation types.
Q. Our house was built in the mid 1800s. It has a stone foundation. About 12 years ago, the north wall of the foundation had so deteriorated that it was replaced with a poured concrete wall. Eight inches of small stones were laid over the dirt floor.
Although I haven’t noticed any water on the stones there is moisture from the dirt floor. I am planning on laying plastic down but I am concerned that holes would gradually appear in it due to contact with the stones. What would you suggest?
I am also thinking of covering the plastic with linoleum loosely laid down to make walking easier.
A. Either get some waste plastic from a construction site (builders have tons to get rid of) and place several layers on the stones before laying a clean sheet over them or put down several layers of new plastic. Instead of linoleum, use old synthetic carpeting. You may be able to get some from a carpet installer who has removed it from a job and has to dispose of it.
Why use pea stones?
Q. We have purchased an old house with an artesian well in our dirt-floor cellar. We have been advised to put down heavy plastic covered with fine pea stones and flagstones. Pouring concrete would be very expensive.
There are no windows in the cellar and not enough headroom to stand upright. My father-in-law says that if we put plastic down, we will be encouraging mold, beetles and other critters. Our neighbor says that in winter, when the house was unoccupied, the windows were encased in ice, but the house plumbing was drained so I don’t know where the water could be coming from.
A. The moisture from the cellar was responsible for the ice on the windows. Covering the bare soil with plastic is the way to go, but why cover the plastic with pea stones and flagstones if there is not enough headroom for the cellar to be useable?
The plastic will not encourage mold or beetles. On the contrary, by containing the moisture in the soil, it will help dry the cellar. Boards can be used for foot traffic.
Q. How can I get rid of a pervasive musty odor that seems to emanate from my dirt floor cellar and permeates the house? The cellar walls are built of loose stones; the ceiling is so low we have to walk in a crouch. Though we don’t use it often, we do store vegetables and preserves in it, and the steam boiler, which needs periodic maintenance, is in it.
Someone suggested placing insulation between the old logs serving as floor joists and tacking plastic underneath the logs as a way to keep the moisture out of the house.
A. Cellars built with old stones and having a dirt floor offer particular challenges. Prior to our tightening up houses to save energy, the problem was not as severe because these old houses were so leaky that the frequent air changes diluted the moisture.
But, since many of these old houses have now been retrofitted, the relative humidity in them has increased to unhealthy proportions, and excessive dampness has become a problem. Mold, mildew, and fungi are also responsible for allergic reactions.
The idea of insulating the cellar’s ceiling and sealing it with plastic is not sound. Since it’s impossible to make the seal tight, moisture would work its way into the insulation and be retained there, hastening the rot of the old logs, which may already be suffering from some decay.
Another problem would develop, making this situation worse. In winter, moisture from the house’s interior would condense on the upper side of the plastic and add to the unhealthy environment in which the logs now find themselves. The reason they lasted so long is that they were able to breathe.
Your situation is common to all old houses with stone cellars and dirt floors. I have worked with many of them and recommend a different strategy. They all leak from rain and melting snow, and because the grading around them is often very poor, the first thing to do is to change the grade as needed to shed water away from the house.
This may not solve the problem in its entirety, but it will certainly help.
Inside the cellar, first remove all the junk and old appliances that are often left there by tradesmen. Then smooth the dirt floor, removing sharp stones and anything else that would damage the vapor retarder to be applied.
Next, dig a shallow trench against the perimeter of the walls and place the dirt as a berm on the side of the trench, away from the walls. This is to catch water leaking through the walls and direct it to a sump, or let it percolate through the soil without running all over the cellar.
Now, if the cellar dirt is relatively smooth, without many sharp stones, etc., you may lay a couple of layers of waste plastic (something contractors are usually trying to get rid of) as a cushion, and cover that with new 6-mil polyethylene. Have the plastic go over the perimeter berm. If you can get more waste plastic, lay it on top of the new sheet, to protect it against damage from walking on it.
Install a sump pump in an appropriate corner, if necessary. If the cellar floor is too rough to smooth it properly so it won’t damage the plastic, you can spread fine sand over it before installing the plastic. Add boards or scrap pieces of pressure-treated plywood for walking access.
Crawl spaces are easy to forget about until problems occur. Sometimes, they’re so shallow that they’re almost inaccessible. But they serve the same basic needs as other foundations; they need to be solid and supportive of the main structure. They need to be protected from moisture. Without proper insulation, they can make the rest of the house uncomfortable.
Q. I’ve had a large pile of old wood in my half basement for 15 years. I’m concerned about bugs or termites living in the wood. If I have the wood removed, I’m afraid whatever termites may be under it may scatter and come up into my house. Since I don’t go into the basement, as it is only 3½ feet high, I have no proof that the spiders and other occasional bugs I find in the house are the result of the wood in the basement. Are my fears about insects living in the wood unwarranted? How should I approach this dilemma?
A. The wood should be moved out of the crawl space; it should not have been put there in the first place. It is definitely an attraction to wood-eating insects like termites. But you have no need to worry about them scattering and coming into your house if they are disturbed by removal of the wood, as they need contact with the soil.
However, you may want to have the crawl space checked and, if need be, treated by an independent pest management professional.
Water condenses in crawl space
Q. I have a split-level with a crawl space under the main floor of the house. The crawl space has a cement floor, with rigid pink insulation foam board covering the cinderblock walls.
There is R-19 in the rafters with the paper facing the floor of the room above the crawl space and three 6-inch x 9-inch screened openings to the outside for venting. Every year the rafters and the insulation get so damp that water droplets form on them. Water actually drips off of the gas pipes, water lines and insulation in the crawl space.
I put a large fan in the crawl space and after a few days it seems to dry everything out. Why does this happen and what can I do to prevent it from happening again?
A. The outdoor, humid air of summer gets into your crawl space that is kept cool by dint of its being in contact with deeper, cooler soil. Some building codes still erroneously specify crawl space ventilation, although it is well-documented that in most climates — and particularly in warmer, more humid areas such as the southeast — this ventilation has been responsible for major structural-rot problems.
Newer science recommends not ventilating crawl spaces as long as the floor is protected from soil moisture by a sheet of 6-mil plastic or a concrete slab. Since your crawl space has a concrete floor, there is no need for additional measures. Close all vents and see if it solves the problem. You may need to put a dehumidifier in the crawl space until the moisture level is greatly reduced.
Q. We live in a 130-plus-year-old house. Our bedroom is on the ground floor with only a 6-inch crawl space beneath it.
The cold air blows through the stone foundation keeping the floor and the room very cool and expensive to heat.
Is there a way to insulate this crawl space? Can anything be blown-in as it is too small an area to get into? If not, what is the best way to insulate the foundation?
A. Such a shallow crawl space in an old house is sure not to have a plastic vapor retarder on the bare soil. Moreover, your area has a lot of clay soil and, more than likely, the soil in the crawl space is damp.
I know of nothing that can be successfully blown-in under the circumstances you describe and, if I did, I would not recommend it. Air is needed to help dry the wood members forming the floor, if indeed they can be.
The air infiltration through the stone foundation is a blessing and probably the only thing keeping your floor from rotting.
When the cold weather arrives, do what the old-timers did. Get some mulch hay bales from a local farmer, stack them tight against the foundation, force loose hay between them and the stone walls to keep the wind out. Cover the whole thing with plastic tacked to the house with wood strips and tuck the plastic under the bales or weigh it down with heavy stones.
Be sure to remove everything in April to get the air to circulate in the crawl space again.
Insulating a wet crawl space
Q. The old part of my ranch house has a four-foot crawl space. I have had installed automatic louvered vents that purportedly close when it is cold and open when it is hot. There is no insulation in the “ceiling” of the crawlspace.
I put an addition on, which also has a four-foot craw space with non-automatic vents. The contractor insulated the “ceiling” of the crawlspace. The house is heated and cooled with forced hot air by way of ductwork in the crawlspaces. However, during the hot summer months with the A/C on, the insulation gets very wet with condensation.
I’ve heard conflicting theories. Some say that if a crawl space is vented, you should not have insulation. Others say insulation is good. I do not think that the condensation is a good thing. Should the insulation stay or go?
A. Recommendations for the treatment of crawl spaces have dramatically changed in the last 20 years or so. Most building codes still specify ventilation although it has proved to be the wrong thing to do. The best strategy for crawl spaces is to thoroughly cover the bare ground with 6-mil plastic.
If the crawl space leaks, fix any grade problems outside to keep water away from the foundation, but bring the plastic up the walls to a point a few inches higher than the outside grade and tape it to the walls. Make sure that the plastic applied to the walls is under any plastic you will need to add on the soil (if the wall plastic is on top, any water will flow right over the floor plastic.)
Close the vents permanently: venting a crawl space in winter makes the floor above cold and in summer, it introduces huge amounts of moisture in a cool space. This is probably responsible for the condensation you have experienced if you live in a moderate to warm climate.
It is best to insulate the walls of the crawl space with extruded polystyrene rigid insulation. Don’t forget to insulate the band joists as well. This will condition the crawl space, which now robs a lot of heat from the ducts in winter and increases the loads on the air-conditioning in summer.
Installing radiant heat in crawl space
Q. I live in a 25- to 30-year-old, 1600-square-foot ranch. I have been trying to improve the energy efficiency over the two years that I have owned it, including adding insulation and replacing windows.
One room is the width of the 2-car garage, located at the back of the garage and about 10 feet deep. It has just a crawl space under it and is on a different zone on the forced hot-water baseboard heat. I am thinking of converting to radiant floor heat as everything is exposed in the cellar. Can I do that in the cold crawl space? How would I insulate and protect it in there?
A. I don’t see any reason why you can’t convert to radiant heat in the crawl space. If it is properly installed by experienced contractors, it should work fine. But select the contractor carefully. I have seen an installation where the contractor used nails and staples to fasten the radiant tubing in spite of the fact that the manufacturer expressly warned against it. The tubing was drooping and leaks were not far behind.
The tubing needs to be straight, held about 1-inch below the subfloor by approved fasteners that are spaced according to the instructions to avoid sagging. Reflective pans are installed below the tubing, and the rest of the floor joists’ depth is filled with fiberglass of the recommended R-factor, considering the make-up of the floor above. The tubing should also be installed so that it avoids as many concealed couplings and joints as possible. This is not a job for amateurs.
Crawl space insulation falling down, moisture building
Q. We live in a home with a crawl space that is only about two feet tall. The insulation has all fallen down and sometimes we have a small area with a little water. We live just 3 blocks from the ocean and want to know what kind of insulation would be best for this situation.
We also have a lot of condensation in the attic. The plywood is wet and the nails drip water. Do you recommend a ridge vent? I would appreciate any advice you can give me as we are new to this area and don’t know what to do. Thank you.
A. I assume that the crawl space soil is bare and not covered with a 6-mil plastic vapor retarder. This is likely to be responsible in great part for the attic’s problem. It is also likely to be responsible for the insulation falling out between the floor joists; the paper vapor retarder holding it up may have rotted away.
I suggest you remove all the insulation batts. If they are in good shape and not soaking wet, and the paper vapor retarder is still sound, use them to insulate the walls of the crawl space. If they are wet and the paper is rotten, put them in heavy contractors trash bags and throw them away.
The first thing to do is to cover the crawl space floor with 6-mil plastic being careful to bring the plastic up the walls to the outside grade level. Since you have had some water seepage, install the plastic on the walls first by stapling it to the mudsill onto which the floor joists rest. Be sure that this plastic is wide enough to cover as much of the soil as possible.
Next, put another sheet of plastic on the ground from wall to wall, overlapping the plastic that is covering the walls as much as possible. This will prevent water from seeping onto the plastic where it cannot be absorbed by the soil. If the fiberglass batts are usable, staple one of their ends to the mudsill and let them hang down to the floor, bending them to cover the floor by a foot. Place bricks, stones or whatever you can find (except untreated wood) on the flat part of the batts against the walls to hold the insulation tightly. Use a stapler to staple the flanges of adjacent batts together.
But if the fiberglass batts are not useable, adhere 1-inch thick extruded polystyrene rigid insulation (blue, grey, pink or green, but no white expanded polystyrene beadboard) to the walls after cleaning them with a stiff brush. Apply daubs of StyroBond or polyurethane caulking to the concrete and press the insulation boards into the adhesive. Then staple plastic to the mudsill, covering the insulation following the instructions above.
Now check the grade outside and make sure it slopes away from the foundation.
Next, check for any convective paths from the living quarters into the attic and seal them up. If you can do the crawl space work and take care of any convection over the winter, wait to see what happens to the attic next winter after it has had a chance to dry over the summer. If you find new condensation, then more investigation will be needed to determine the best methods to ventilate the attic.
Keeping water away from crawl space
Q. We moved into our house three months ago and discovered that water is coming into the crawl space through the footing.
There is 6-mil plastic on the ground of the crawl space but it isn’t in very good condition. Any suggestions?
A. You should definitely have the plastic repaired by putting a new sheet over the existing one in all areas where the ground isn’t completely covered. But that doesn’t solve your leakage problem; it only prevents soil moisture from evaporating and getting into the rest of the house.
You should attempt to stop the leakage from outside by repairing any negative or flat grade that allows water to run toward, or collect near, the foundation. Make sure that all downspouts discharge properly onto splashblocks and that the latter are sloped away from the house.
If there are any patios, walks, stoops, and driveways that direct water toward the house, they also need to be repaired.
If all is well with the grade and additions, you may have an underground water problem. This is more difficult to deal with, but it is also much rarer.
Protecting a shallow crawl space
Q. My small basementless house has had two additions to it. The back porch was enclosed and its crawl space has two vents. The garage was converted into two bedrooms and a new garage was built next to it.
The crawl space under the bedrooms has only one vent, which goes into the new garage. A year ago that space seemed dry. It isn’t deep enough to crawl in, and there are no pipes in it. Should I fill this space with foam insulation?
A. Do you want to make the floor warmer, or are you concerned about moisture? If it is to make the floor of the bedrooms warmer, the floor should have been insulated between the floor joists before the subfloor was put on permanently. Since there isn’t enough room to crawl in, you can forget that now. You would have to insulate the foundation from the outside with 1-inch extruded polystyrene rigid insulation and cover it with a compatible cement coating or half-inch pressure-treated plywood. The plywood would have to be properly flashed to the siding. But this should be done only if the ground is completely covered with 6-mil plastic. Otherwise you will be trapping moisture in the crawl space.
An alternative is a thick synthetic pad and carpet.
Since your former garage probably had a concrete slab, it is less likely to have a problem than if it were bare soil, but you are wise to keep an eye on it periodically.
I would urge you emphatically not to blow foam in to fill the crawl space. Have you checked the other crawl space? If the soil is bare, it should be covered with heavy plastic if there is access to it.
Turning crawl space into full basement
Q. The foundation of my house is half basement and half crawl space. I am in the process of digging out soil and rock from my crawl space to make it into a full basement. I am doing this with 5-gallon plastic pails, averaging about 15 pails a week. I calculated that it would take me at least two years to complete the dig. I don’t want to hire a contractor; I want to do the job myself. How can I finish the job faster and simpler?
A. You are one ambitious fellow, but I guess it’s time better spent than gambling or whatever. You could do what we used to do when I was doing this sort of work as a contractor: Rent (or buy) a conveyor belt and have it dump the dirt and rock into a wheelbarrow. Of course that requires a window or a removable vent, if there is one in a convenient place. If not, I can’t think of any other way to speed the work and make it easier with the constraints you have put on yourself.
However, I would caution you to be very careful not to endanger the structure of your house. Usually, the foundation walls of a crawl space are shallower than those of a full basement. If, in digging the space out, you undermine the foundation, you risk some major structural problems. If you need to dig below the bottom of the footings, you have two choices:
- One choice is to leave a slope of 45° from the base of the footings to the bottom of the excavation. This would make the floor space much smaller, depending on how far below the bottom of the footings you plan to go.
- The alternative is to work in short alternating sections of no more than 4 feet, leaving 8 feet between digs. When one section is done, excavate another 4 feet and so on. Pour concrete footings, and build a 12-inch thick masonry wall no closer than 2 feet from the footings.
If you can do this yourself, more power to you, but it is work generally better left to experienced contractors.
Replacing the plastic on dirt floor of crawl space
Q. We have a summer home in Brigantine, NJ which is a 1950s split level with hot water baseboard heat. The crawl space below the kitchen and living room has a dirt floor which is presently covered with plastic (in very poor shape). The kraft paper on the insulation on the floor joists is dripping water.
I know the plastic must be replaced but am wondering what is the proper way to do this. While doing this, would it be advisable to glue 2? foam insulation to the 3 exterior walls and regular insulation to the studded interior wall to help in keeping the area warmer during the winter to prevent the water pipes to the kitchen and bathrooms from freezing? There are also hot water heating pipes that run through this crawl space. Some of the pipes are insulated with foam insulation and some are not. Would it also be advisable to block the two vents in the cinder block foundation during the winter?
Last winter I checked the temperature in the crawl space and it was approximately 45 degrees F when the outside temperature was in the 20s. The heat in the house is left on at 50 degrees F all winter. Any information you could provide would be helpful.
A. You can leave the existing plastic in place and put another layer of 6-mil plastic over it. Be sure it covers the entire crawl space. Overlap any joints by a couple of feet and, if you experience leakage through the walls, bring the plastic up the walls to a point above the outside grade. Tape it in place with duct tape after brushing the spots clean so the tape will adhere.
Remove the wet insulation and dispose of it in heavy plastic bags; do not replace it. Cover exposed skin with cream, wear a dust mask, a plastic shower cap, tight clothing and eye protection, and thoroughly shower afterward. Adhere 2-inch thick extruded polystyrene to the masonry walls with dabs of Styrobond or polyurethane caulking on clean surfaces. Staple fiberglass to any frame wall facing outside, but there is no need to insulate an interior wall; it is best to let all inside spaces “communicate”. Insulate the non-insulated heat pipes with neoprene foam.
Finally, close the foundation vents year-around. In summer, they introduce a lot of moisture—probably the reason why the fiberglass floor insulation is dripping wet. Once you have added new plastic to the floor, there should no longer be a moisture problem.
Should floor joists be insulated?
Q. Should I use unfaced fiberglass insulation or insulation with an integral vapor barrier between the joists of my basement ceiling to keep the upstairs floor warmer? Should the insulation be tight to the subfloor above or should I leave an air space?
I have a separate crawl space that is unvented and has a gravel floor. The existing insulation is installed with the vapor barrier down. I want to redo that, too, and have the same questions as for the basement.
A. You should consider insulating the walls of the basement and crawl space instead of their respective ceilings. This is particularly sensible in the basement, as you must have water pipes and a heating plant in it. Why lose the benefit of the radiation and stand-by losses of the furnace when you could capture them and make the basement warmer? The same should be considered for the crawl space, particularly if there are any water pipes or ducts running through it. In both cases, if the soil around the house is clay or other heavy soil, you should insulate foundation walls to a depth of only two feet below grade.
The most important thing to do in the crawl space is to cover the ground with 6-mil plastic, making sure you do a thorough job.
Remove a few pieces of the existing insulation to see if it is wet and if the floor joists and plywood subfloor show signs of dampness or mold. If so, the insulation should be removed at once, laid on the plastic to dry, and a dehumidifier set in the crawl space to remove the excessive humidity. (If you don’t own one, try to borrow or rent one). This will take some time.
If all is well, and you wish to properly insulate between the joists, take your time to turn the insulation over, install it tight to the subfloor, and hold it in place with nylon string stapled zigzag to the sides of the joists, or use tiger’s teeth (pointed metal pieces available in building supply houses). If you decide to insulate the perimeter instead, you can re-use the insulation on the walls and band joists.
Placing plastic in inaccessible crawl space
Q. I would like to cover the bare soil in the crawl space of the addition to our house with 6-mil plastic, but I can’t get in there as the floor is too low. Can I have insulation blown in, or is there some other solution?
A. Blowing insulation would only make a bad situation worse. It is generally possible, using an Army folding shovel, to dig a trench in the center of the crawl space of an addition. Place the dirt on one side and, when done trenching, push plastic in place on the side without the dirt with a soft-bristled broom so as not to damage the plastic. Make sure it’s tight against the walls; better yet, have it go up them a few inches. Then, use the shovel to pick up the dirt and heave it, as best you can, over the plastic toward the walls or place the dirt as far as you can and push it with the broom. Then do the other side.
Finally, lay a piece of plastic to overlap the other two pieces generously, and cover the trench as you retreat.
Protecting water pipes in crawl space
Q. The pipes in my crawl space freeze when the temperature drops below minus 10°F. So far I have been lucky, no pipes have burst but no water comes out of them. I am considering wrapping heat cables around them as the hardware store clerk suggested, but I am concerned that it will raise my electric bill considerably.
A. The greater concern is the risk of fire. A number of fires and some deaths have been attributed to heat cables. It is much safer and cheaper, in the long run, to insulate the pipes and the top of the foundation to 2 feet below the outside grade. You can do that from inside the crawl space with either rigid extruded polystyrene (blue or pink) or fiberglass batts. You can do it from the outside with polystyrene, protected by pressure-treated plywood and proper flashing.
However, if you insist on using heat cables, be sure that the type you buy is UL listed.
Is venting necessary?
Q. There are two small vents in our crawl space that remain open year around. In the summer, we also open the screened entrance to the crawl space. The crawl space floor is dirt.
Our house has forced air heat and air conditioning, and all ductwork and plumbing pipes are in the crawl space.
Should the crawl space be vented, or should the vents be closed? We are getting conflicting advice.
A. If it is not, the crawl space floor should be thoroughly covered with a 6-mil plastic sheet to control soil moisture. It may not seem as if there is any moisture exuding from it, but there is.
The vents and the entrance door to the crawl space are best kept closed. In winter, with the vents open, your furnace is working overtime to satisfy your needs, and the plumbing pipes are at risk. In summer, huge amounts of moisture are absorbed by all the wood in the crawl space (i.e. floor joists, subfloor and any other wood members) and that moisture is released during the heating season adding to the moisture in the house.
If you control the soil moisture, venting a crawl space is not advised. But, to be sure, from time to time, enter the crawl space and give it the nose test. If it smells good and no musty smell is present, all is well. But if you smell mustiness, open the vents and the door during the dry and breezy times of the year in spring and fall.
Crawl space ventilation
Q. When we had an addition with a crawl space built we were advised to keep two small cellar windows open into the crawlspace for ventilation. Since that time one of the windows has been used for heat vents from our new furnace. The other window is kept open a small amount, however, it is right over our pellet stove which is in the cellar and I feel that we are losing a lot of the heat from the pellet stove into the crawl space.
Can we close this window during the heating season without having moisture build up in the crawl space?
A. If the dirt floor of the crawl space is thoroughly covered with 6-mil plastic to control soil moisture, and the grade is sloping away from the foundation to prevent water penetration, there is no need for ventilation. Crawl-space ventilation can cause problems, especially in moderate to warmer climates.
But if the foundation walls of the crawl space are insulated either from inside or outside, and not between the floor joists, the heat from the pellet stove will make the floor above the crawl space warmer—a real plus. You can regulate the amount of heat going into the crawl space by adjusting the opening of the window.
Protecting ductwork and pipes
Q. My crawl space is approximately 4 feet deep. The dirt floor is covered with heavy plastic. The ductwork is very leaky, so much so that in winter, if the foundation vents are left open, a considerable amount of warm air comes out through them, and in summer cool air comes out. There are also water pipes running through.
Obviously, the ductwork needs attention, but I do not want to seal and insulate it, which could result in frozen pipes and cold floors.
A. Although building codes specify crawl-space ventilation, research done years ago by the National Association of Home Builders Research Foundation (now called the NAHB Research Center, Inc.) found that, in most cases, crawl-space ventilation was actually detrimental if the bare soil was thoroughly covered with plastic or a concrete slab. In humid southern climates, open vents actually caused extensive condensation and rot.
You should seriously consider taping the ductwork joints with special tape you can get from a heating contractor and closing the vents year around. Also, consider insulating the inside of the foundation with 1-inch-thick rigid foam insulation from the floor joists to no lower than 2 feet below grade. The reason for this, as you are inquiring in your letter, is to avoid risking cracking foundation walls from deeper frost penetration since heat loss through them is greatly reduced.
Your crawl space will be warmed sufficiently by the heat loss from the first floor, so you should not be concerned about frozen pipes even if you decide to have the ductwork insulated—not a bad idea. It should save you a considerable amount of money summer and winter alike. You do have a very wasteful system.
But before you install rigid insulation on the inside of the crawl space’s exterior walls, have a pest management professional treat the soil next to the walls to prevent termite infestation that could occur undetected behind or through the insulation.
Q. We are in the process of adding a four-season sunroom on the east side of our house. We put in a 5-foot frost wall, filling it to grade level with sand, then put a vapor barrier on the sand with another 2 to 3 inches of sand on top of the vapor barrier. The exterior wall was coated twice with waterproofing, and drainage was installed all around it. However, the natural grade of the land on one side is a slope toward the sunroom. When the excavating is done, there will be a swale away from it. The sunroom has now been framed in, and the windows and doors have been installed.
We are now experiencing very wet sand in the crawl space on top of the vapor barrier—so much so that the new nails from the floor construction have already rusted. We can make balls with the sand, but there is no standing water on the vapor barrier. We did get three heavy downpours during the construction, but we had it covered with a tarp and feel all of this wet sand cannot be from rain getting in. We have been running a fan and dehumidifier in the crawl space with very little result. The floor needs to be insulated, but the contractor will not do so with this moisture problem. The soil around our home is heavy clay.
Ten years ago, we put an addition on the west side of our house and used this same method and have never had any problems with moisture. The nails look like new under the floor, and the sand there is completely dry. We are at a loss as to what we need to do, and what could be causing this problem.
A. Check to see if there is moisture beading under the plastic vapor barrier; that may tell you if there is a lot of moisture coming up from the ground by capillary attraction or if there is leakage through the foundation. These conditions could be responsible for the problem if the plastic is not fully and properly installed. If the underside of the plastic is dry, this should reassure you that the waterproofing is working.
As for the wet sand on top of the plastic, my guess is that either the tarp did not stop all the water from the three downpours and that the sand got wet, or that the grade sloping toward the sun room (before the swale is put in) allowed surface water from the three downpours to get inside the crawl space in spite of the exterior waterproofing. It will take a long time for the sand to dry, and your builder is right in not wanting to insulate the floor until this condition is taken care of.
The best way to dry the sand is to introduce heat into the crawl space coupled with a small fan exhausting the heated and moist air to the outside. If you use a jet heater (your builder can supply one), you won’t need an additional fan as it provides its own powerful thrust. But you will need an intake of exterior air to replenish the air that is exhausted out. You may have to cut openings in the floor at opposite ends of the crawl space to allow for good circulation. Be sure to keep all sunroom windows fully open. You should also stir the sand every day to bring the wet sand to the top of the bed.
Another way to handle the problem is to cut the plastic and pull it up in sections and let the wet sand mix with the other, dry sand. Then cover the entire crawl space with new 6-mil plastic, carrying it up the foundation walls a foot or so and taping it to the concrete walls. No need to put more sand on top of the plastic.
Dryer vent in crawl space
Q. My dryer vent is terminating in the crawl space. Would it be what is causing the floor boards to buckle in the center of my hallway?
A. It could indeed. A dryer vent should always terminate outdoors.
Insulating cottage floor above crawl space
Q. The kitchen floor of my cottage cannot be insulated from underneath because of the lack of clearance. Since it is used during the winter, is there a way to insulate on top of the existing floor? I can raise the floor 2 inches without any problem.
A. Use 1½-inch-thick extruded polystyrene rigid insulation (Styrofoam or FoamulaR) and cover it with ½-inch plywood. But if there are water pipes and drains running through the crawl space, it is best to insulate the perimeter of the crawl space walls from the outside.
Kitchen addition over crawl space is cold
Q. The addition to the kitchen in the house I bought last year is always 10° colder than the rest of the house and when the furnace fan comes on it feels like air-conditioned air coming out. By the time the air warms up, the fan shuts off.
There are 2 inches of Styrofoam insulation on the exterior walls of the crawl space but I don’t know how deep in the ground the insulation extends; there is an outside access door. The crawl space is about 2 feet deep below the joists and the dirt is covered with plastic. How can I make this room extension warmer?
A. You haven’t mentioned any insulation on the band joists (perimeter joists of the floor system). If this area is not insulated, it should be, as much heat is lost there. Use R-19 (6-inch) fiberglass batts with an integral vapor retarder. Cut the pieces needed at the ends of the joists 1 inch longer than the depth of the joists and squeeze them in over the wooden mud sill bolted onto the foundation and on which the joists rest.
Staple the insulation’s side flanges to the sides of the joists and the excess inch of paper to the mud sill. Where the band joists are parallel to the other joists, cut a strip of insulation lengthwise instead of crosswise and 1 inch wider than the joists’ depth. Staple the remaining flange to the floor sheathing above and the excess paper to the mud sill.
Fasten a piece of rigid foam insulation behind the access door and insulate the ducts with special duct insulation that you’ll probably have to buy from a heating contractor. If there is no room to wrap insulation around the ducts, insulate the sides and bottom of the joists between which they run with regular fiberglass batts and, where they run beneath the joists, drape insulation around them as much as you can, making sure that you have slipped pieces of insulation between the joists immediately above the ducts so they are completely surrounded.
Q. I have a 12×13-foot addition built on Sonotubes (poured concrete piers), and would like to close in the underside, both for aesthetics and to keep the floor warmer. The floor is insulated with 6 inches of fiberglass but is still cold. I am considering closing in the perimeter with ½-inch pressure-treated plywood. I would paint the bottom edge with black roofing cement where it comes into ground contact.
The area is fairly well drained. I know there could be some movement in winter but assume the worst it would do is buckle the plywood. Is this a good idea? Also, would I gain much by backing the plywood with 1-inch foam?
A. There is no reason why you can’t do what you have in mind, but I would suggest that you make sure the soil under the addition is sloping away from the house foundation wall so no water can run back under the addition.
I would also cover the soil with 6-mil plastic to keep moisture from getting into the insulated first-floor system, where it would cause eventual structural damage. There is no need to coat the bottom edge of the pressure-treated plywood with roofing cement. Not only are the plywood edges treated, but the cement will eventually degrade from contact with the soil. It would be best to bury the plywood skirt by at least 6 inches.
Considering that the underside of the floor is insulated with fiberglass, there might not be much to gain from insulating the plywood skirt with rigid insulation, but it’s worth a try. You should also provide an access panel to check the underside of the addition yearly to make sure all is well.
