Wall and roof intersectionsThis section covers weather protection. Although short, the importance of becoming familiar with the provisions of this section is not to be taken lightly. I am going to review the provisions of weather protection regarding roof decks first and all others will fall into place from there. I do want to note that in some chapters of this book, I mentioned that some words could be used interchangeably. This chapter, however, contains words and phrases that cannot be used in this manner. For instance, there is a difference in definition between roof coverings, roof deck, and rooftop structure. I have added these as definition alerts for you.
Roof decks are required to be covered with an approved roof covering. These must be secured to the building or structure in accordance with this chapter. All roof coverings must be designed, installed, and maintained in accordance to this code. They must also follow the manufacturer’s instructions in that the roof covering will protect the building or structure.
!Definition alert |
Roof deck: The flat or sloped surface not including its supporting members or vertical supports. |
Flashing is an integral factor in a building’s ability to resist water intrusion and must be installed in such a manner to prevent moisture from entering the wall and roof through joints, materials, and at intersections or through the roof plane. Attention to this important aspect of building performance is necessary in both the design and installation of your building project. Metal flashing must be corrosion resistant with a thickness of no less than 0.019 inch. Please see the following list regarding the locations in which flashing must be installed:
Wall and roof intersections
Gutters
Changes in roof slope or directions
Around roof openings.
All parapet walls must be properly coped with noncombustible, weather-proof materials. The width of the materials cannot be any less than the thickness of the parapet wall. I’m sure you are aware that a new building or structure will need a roof drainage system. If you didn’t know that, you do now. Any design and installation of roof drainage systems must be done in compliance with The International Plumbing Code.
Gutters and leaders that are placed on the outside of buildings have to be made of noncombustible material or a minimum of Schedule 40 plastic pipes. Buildings in Group R-3, private garages, and buildings of Type I construction are not to be included as buildings that must follow is code provision. And all roofs decks must have intake and exhaust vents that are installed according to manufacturer’s guidelines.
CODE UPDATE |
An enclosed, unoccupied structure above the roof of a building, other than a tank, tower, spire, dome cupola, or bulkhead is a penthouse. |
Wind resistance roof requirements are a serious matter. Just watching the news and hearing about the tremendous damage caused by high winds, heavy rains, and hurricanes is enough for anyone to realize how important the provisions of this section are.
Roof decks and roof coverings must be designed for heavy wind loads. This section will focus more on the testing of roof elements and roof systems and how they must conform to this code.
Roof systems with built-up modified bitumen, either fully adhered or mechanically attached through fastened metal panel roof systems, and other types of membrane roof coverings must be tested in accordance with FM 4450, FM 4470, UL 580, or UL 1897. If you have a metal panel roof system through either fastened or standing seam, also must be tested with UL 580 or ASTM E 1592. An exception to this are metal roofs that are constructed of cold-formed steel, where the roof deck acts as the roof covering and provides both weather protection and support for structural loads. These are permitted to be designed and tested in accordance with the referenced structural design standard of this code. For your information, I have listed the acronyms used in the paragraph above:
!Definition alert |
Roof assembly: A system designed to provide weather protection and resistance to design loads. The system consists of a roof covering and roof deck or a single component serving as both the roof covering and the roof deck. A roof assembly includes the roof deck, vapor retardant, substrate or thermal barrier, insulation, vapor retardant, and roof covering. |
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The height of a building is also taken into consideration for the allowance of gravel and stone. The regulations regarding the maximum allowance for roof height permitted for buildings with gravel or stone on the roof in areas outside a hurricane-prone region are addressed in the code. |
FM: Factory Mutual Research
ASTM: American Society for Testing and Materials.
With these acronyms handy, it will be easier for you to refer to these standards to be sure that your building’s components are correctly installed.
The physical properties required for roof coverings installed on low-slope roofs must demonstrate physical integrity over the working life of the roof based upon 2000 hours of exposure to accelerated weather testing that must be conducted in accordance with ASTM G 152, 155, or 154. Roof coverings that are subject to cyclical flexural response due to wind loads cannot demonstrate any major loss of tensile strength.
Roof assemblies are divided into classes of A, B, and C. The minimum roof coverings installed on buildings must comply based on the type of construction of the building.
Class A roof assemblies are those that are most effective against severe fire exposure. All Class A roof assemblies and coverings must be listed and identified as such, by an approved testing agency. You may use this class for all buildings or structures of all types of construction, except for Class A roof assemblies with the following coverings:
Brick
Masonry
Slate
Concrete roof tile
Exposed concrete roof deck
Ferrous or copper shingles or sheets.
Class B roof assemblies are those that are effective against moderate fire-test exposure and must be listed and identified as such by an approved testing agency. An exception is Class B roof assemblies including those with coverings of metal sheets and shingles.
Class C roof assemblies are those that are effective against light fire-test exposure. Class C assemblies must also be listed and identified by an approved listed agency.
There are applicable standards that materials must conform to, but if the materials are of a questionable suitability, testing by an approved agency is required by the building official to determine the quality or any limitations of application of the materials.
If you are receiving your roofing materials in bulk shipments there are a couple of things to be aware of. First, all materials must have all information issued in the form of a certificate or on a bill by the manufacturer. Second, all materials must be in packages that have the manufacturer’s identifying marks and approved testing agency labels. This is a requirement of this chapter.
Provisions of requirements for roof coverings include the way in which roof coverings are applied. This includes the manufacturer’s installation instructions. For roofs located in areas where the basic wind speed is 110 mph or greater, asphalt shingles must be tested in accordance with ASTM D 3161, Class F.
CODE UPDATE |
A roof assembly is a system designed to provide weather protection and resistance to design loads. |
Asphalt shingles must have self-seal strips or must be interlocking. All packaging must have a label indicating compliance or a listing by an approved testing agency. Now don’t think that you can use any type of fasteners for this type of shingle. All fasteners for asphalt shingles must be galvanized, stainless steel, aluminum, or copper roofing nails. These nails must have a minimum 12 gage shank with a minimum diameter head of 0.375 inch.
If roof sheathing is less than 0.75 inch, you must be sure that the nail will penetrate. The code requires that there are a minimum number of fasteners per shingle—no less than four fasteners per strip shingle or two fasteners per individual shingle. There has been a change in the code regarding the underlayment application for roof slopes. Distortions in the underlayment must not interfere with the ability of the shingle to seal.
Roof slopes of four units vertical in 12 units horizontal or greater, under-layment must be one layer applied in the following manner. Underlayment must be applied shingle fashion, parallel to and starting from the eave and lapped 2 inches, fastened sufficiently to hold in place.
As you are aware, various exterior building elements such as roofs, walls, windows, and doors form a packet that protects the inside of the building from elements; water being the biggest threat. Obviously a roof with appropriate drainage minimizes this, but buildings need more than just a roof, which brings me to the installation of flashing and why it is so important. Installed at intersecting roofs and parapets, this corrosion-resistant metal overlaps to discourage water entrapment.
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Distortions in the underlayment must not interfere with the ability of the shingles to seal. In areas of high winds (over 110 mph), underlayment must be applied with corrosion-resistant fasteners, and must be applied along the overlap at a maximum spacing of 36 inches on center, making sure to follow the manufacturer’s instructions. |
!Definition alert |
Underlayment: One or more layers of felt, sheathing paper, nonbituminous saturated felt, or other approved material over which a steep-slope roof covering is applied. |
Base flashing is the portion of the installation that is attached to the roof itself and cap flashing is attached to the projection or wall. Both must be made of a corrosion-resistant metal.
Valleys occur where the different roof slopes intersect and are considered to be problem spots. Valley linings are to be installed in accordance with the manufacturer’s instructions before applying shingles. For open valleys lined with metal, the lining must be at least 16 inches wide. Lining of two plies of mineral-surfaced roll roofing is permitted with the bottom layer having a maximum of 18 inches and the top layer a minimum of 36 inches.
For closed valleys (valleys covered with shingles), lining of just one ply of smooth roll roofing of at least 36 inches wide is permitted.
Be sure to provide a drip edge at eaves and gables of shingle roofs. Overlap to a minimum of 2 inches and extend 0.25 inch below sheathing. Drip edges must be mechanically fastened a maximum of 12 inches.
CODE UPDATE |
Roof decks are to be covered with an approved roof covering that is secured to the building or structure it protects. |
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Another type of roofing that is used is mineral-surfaced roll roofing that cannot be applied on roof slopes below one unit vertical in 12 units horizontal. You must be careful of the underlayment of this type of roofing. |
When you have a tall projection or structure mounted on pitched roofs, such as a chimney, you must use a saddle or cricket. A cricket is actually a ridge that is installed between the roof slope and the structure. Cricket or saddle coverings must be made of sheet metal or of the same material as the roof covering.
In areas where there has been a history of ice formation, an ice barrier that consists of at least two layers of underlayment cemented together or of a self-adhering polymer-modified bitumen sheet must be used instead of normal underlayment and it must extend from the eave’s edge to a point at least 24 inches inside the exterior wall line of the building. This does not include detached accessory structures that contain no conditioned floor area. The last type of roof covering is wood shingles.
The use of above-deck thermal insulation is permitted provided the insulation is covered with an approved roof covering that passes the tests of FM 4450 or UL 1256. This does not include foam plastic roof insulation, which must conform to the material and installation requirements found in the code or where a concrete roof deck is used and the above-deck thermal insulation is covered with an approved roof covering. If you are choosing to install cellulosic fiberboard roof installation, you must be sure it conforms to the material and installation requirements.
CODE UPDATE |
A cricket or saddle shall be installed on the ridge side of any chimney or penetration greater than 30 inches wide as measured perpendicular to the slope. |
A penthouse or other projection above the roof in structures of other than Type I construction cannot be more than 28 feet above the roof where used as an enclosure for tanks or for elevators that run to the roof and not more than 18 feet for all other cases. A penthouse, bulkhead, or any other similar projection above the roof cannot be used for any purposes other than housing for mechanical equipment or shelter of vertical shaft openings in the roof.
If a penthouse or bulkhead is being used for purposes other than permitted by this section, the use must conform to the requirements of this code. This section does not prohibit the placing of wood flagpoles on the roof of any building. The type of construction for penthouses must include walls, floors, and roofs, required for that building. Exceptions to this include the following:
On buildings of Type I and II construction, the exterior walls and roofs of penthouses with a fire separation distance of more than 5 feet and less than 20 feet must be of at least one-hour fire-resistance-rated noncombustible construction.
Interior framing and walls must be made of noncombustible construction.
On buildings of Type III, IV, and V construction, the exterior walls of penthouses with a fire separation distance of more than 5 feet and less than 20, must be at least one-hour fire-resistance-rated construction.
CODE UPDATE |
Cricket or saddle coverings are to be sheet metal or of the same material as the roof covering. |
Walls with a fire separation distance of 20 feet or greater from a common property line must be of Type IV or noncombustible construction.
Interior framing and walls must be Type IV or noncombustible construction.
Unprotected noncombustible enclosures housing only mechanical equipment and located with a minimum fire separation distance of 20 feet will be permitted.
On one-story buildings, combustible unroofed mechanical equipment screens, fences, or similar enclosures are permitted where located with a fire separation distance of at least 20 feet from adjacent property lines and where not exceeding 4 feet in height above the roof surface.
Dormers must be of the same type of construction as the roof on which they are placed, or of the exterior walls of the building.
All materials that you use to reroof must be of the same quality as if you were constructing new, except that reroofing does not have to meet the minimum design slope requirements of one-quarter unit vertical in 12 units horizontal for roofs that provide positive roof drainage. Structural roof components must be capable of supporting the roof-covering system and the material and equipment loads of the system. There is a very important provision to remember when reroofing. Never install a new roof without first removing all existing layers of roof coverings where any of the following conditions occur:
Where the existing roof or roof covering is water soaked or has deteriorated at the point that the existing roof or roof covering is not adequate as a base for additional roofing
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If the application of a new wood shingle or shake roof covering creates a combustible concealed space, you must cover the entire existing surface with gypsum board, mineral fiber, or other approved materials. |
Where the existing roof covering is wood shake, slate, clay, cement, or asbestos-cement tile
Where the existing roof has two or more applications of any type of roof coverings.
Exceptions to this are:
Complete and separate roofing systems, such as standing-seam metal roof systems, that are designed to send the roof loads directly to the building’s structural system and that does not rely on existing roofs and roof coverings for support, do not require the removal of existing roof coverings.
Metal panel, metal shingle, and concrete and clay tile roof coverings are allowed over existing wood shake roofs when applied in accordance with this chapter.
The application of a new protective coating over an existing spray polyurethane foam roofing system is permitted without tear-off of existing roof coverings.
There are some instances where you may reinstall materials. This applies only to slate, clay, or cement tile that is not cracked, damaged, or broken. You must reconstruct flashings in accordance with approved manufacturer’s installation instructions as well.
CODE UPDATE |
Ice barriers are required on roofs where there is a history of ice build-up on eaves. |
