LENGTH OF SHINGLES (IN.)	EXPOSURE OF SHINGLES (IN.)
LENGTH OF SHINGLES (IN.)	SINGLE COURSE	DOUBLE COURSE
16	6 to 7-1/2	8 to 12
18	6 to 8-1/2	9 to 14
24	8 to 11-1/2	12 to 20

SHEATHING NOTES

• Sheathing may be strip type, solid 1 by 6 in., and diagonal type, in plywood, fiberboard, or gypsum board. Horizontal wood nailing strips (1 by 2 in.) should be used over fiberboard and gypsum sheathing. Space strips equal to shingle exposure.

• Many finishes can be used on red cedar shakes and shingles: solid color or semitransparent (“weathering”) stains, exterior latex paint with primer, wood preservative, and bleaches.

• Breather mats, to allow shingles to be spaced off weather barrier, provide a drainage cavity and vent behind shingles. Mat provides better resistance to weather and longer life for shingles.

• Preferred method: detail sheathing or weather barrier to function as air barrier.

NOTES

2.360 a. With the panel system, shakes and shingles, plus sheathing, go up in one operation: 8-ft roof panels have 16 hand-split shakes bonded to 6- by 1/2-in. plywood strip, which forms a solid deck when the panels are nailed. A 4 to 12 or steeper roof pitch is recommended.

b. After application of starter panels, attach panels directly to rafters. Although designed to center on 16- or 24-in. spacing, they may meet between rafters. Use two 6d nails at each rafter.

c. The 8-ft sidewall panels are of two-ply construction: The surface layer is of individual #1 grade shingles or shakes. The backup, of exteriorgrade plywood shakes or shingles, is bonded under pressure with exterior-type adhesives to plywood backup.

d. Install weather barrier behind panels, lap a minimum of 3 in. vertically and horizontally. Stagger joints between panels.

e. Application types are determined by local building codes.

f. Matching factory-made corners for sidewall or roof panels are available.

Contributors:

David S. Collins, FAIA, American Forest & Paper Association, Cincinnati, Ohio; Richard J. Vitullo, AIA, Oak Leaf Studio, Crownsville, Maryland.

WOOD SHINGLES AND SHAKES FOR SIDING

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EXTERIOR WALL VAPOR RETARDERS, AIR BARRIERS AND INSULATION

BUILDING SECTION ANALYSIS FOR POTENTIAL CONDENSATION

Any building section may be analyzed using simple calculations to determine where condensation might occur and what might be done in selecting materials or their method of assembly to eliminate that possibility. The section may or may not contain a vapor barrier, or it may contain an inadequate one; the building section may include cold-side materials of comparatively high resistance to the passage of vapor (which is highly undesirable). With few exceptions, the vapor resistance at or near the warm surface should be five times that of any components. Table 2.414 supplies permeance and permeability of common building and vapor retarder materials. These values can be used in analyzing building sections by the following simple method:

1. List the materials, without surface films or air spaces, in the order of their appearance in the building section, beginning with the inside surface material and working to the outside.

2. Against each material, list the permeance (or permeability) value from the table, or a more accurate value if available from tests or manufacturers’ data. Where a range is given, select an average value or use judgment in assigning a value based on the character and potential installation method of the material proposed for use.

3. Start at the top of the list and note any material that has less permeance than the materials above it on the list. At that point, the possibility exists that vapor leaking through the first material may condense on the second, provided the dew point (condensation point) is reached and the movement is considerable. In that case, provide ventilation through the cold-side material or modify the design to eliminate or change the material to one of greater permeance.

PERMEANCE AND PERMEABILITY OF MATERIALS TO WATER VAPOR

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MATERIAL	PERM (IN.)^e
MATERIALS USED IN CONSTRUCTION
Concrete (1:2:4 mix)	3.2^e
Brick-masonry (4″ thick)	0.8 to 1.1
Concrete masonry (8″ cored, limestone aggregate)	2.4
Plaster on metal lath (3/4″)	15
Plaster on plain gypsum lath (with studs)	20
Gypsum board (3/8″ plain)	50
Structural insulating board (sheathing quality	20 to 50^e
Structural insulating board (interior, uncoated, 1/2″	50 to 90
Hardboard (1/8″ standard)	11
Hardboard (1/8″ tempered)	5
Built-up roofing (hot-mopped)	0.0
Wood, fir sheathing, 3/4”	2.9
Plywood (Douglas fir, exterior glue, 1/4″)	0.7
Plywood (Douglas fir, interior glue, 1/4″)	1.9
Acrylic, glass-fiber-reinforced sheet, 56 mil	0.12
Polyester, glass-fiber-reinforced sheet, 48 mil	0.05
THERMAL INSULATIONS
Cellular glass	0.0^e
Mineral wool, unprotected	29.0
Expanded polyurethane (R-11 blown)	0.4 to 1.65
Expanded polystyrene—extruded	1.2^e
Expanded polystyrene—bead	2.0 to 5.8^e
PLASTIC AND METAL FOILS AND FILMS^b
Aluminum foil (1 mil)	0.0
Polyethylene (4 mil)	0.08
Polyethylene (6 mil)	0.06
Polyethylene (8 mil)	0.04
Polyester (1 mil)	0.7
Polyvinylchloride, unplasticized (2 mil)	0.68
Polyvinylchloride, plasticized (4 mil)	0.8 to 1.4
BUILDING PAPERS, FELTS, ROOFING PAPERS^c
Duplex sheet, asphalt-laminated, aluminum foil	0.176
one side (43)^d
Saturated and coated roll roofing (326)4	0.24
Kraft paper and asphalt-laminated, reinforced	1.8
30-120-30 (34)^d
Asphalt-saturated, coated vapor barrier paper (43)^d	0.6
Asphalt-saturated, not coated sheathing paper (22)^d	20.2
15-Ib asphalt felt (70)^d	5.6
15-Ib tar felt (70)^d	18.2
Single kraft, double-infused (16)^d	42
LIQUID-APPLIED COATING MATERIALS
Paint—two coats
Aluminum varnish on wood	0.3 to 0.5
Enamels on smooth plaster	0.5 to 1.5
Primers and sealers on interior insulation board	0.9 to 2.1
Miscellaneous primers, plus one coat flat oil paint on plastic	1.6 to 3.0
Flat paint on interior insulation board	4
Water emulsion on interior insulation board
Paint—three coats	30 to 85
Styrene-butadiene latex coating, 2 oz/sq ft	11
Polyvinyl acetate latex coating, 4 oz/sq ft	5.5
Asphalt cutback mastic
1/16″ dry	0.14
3/16″ dry	0.0
Hot-melt asphalt
2 oz/sq ft	0.5
3.5 oz/sq ft	0.1

NOTES

2.363 a. The vapor transmission rates listed will permit comparisons of materials, but selection of vapor retarder materials should be based on rates obtained from the manufacturer or from laboratory tests. The range of values shown indicates variations among mean values for materials that are similar but of different density. Values are intended for design guidance only.

b. Usually installed as vapor retarders. If used as exterior finish and elsewhere near cold side, special considerations are required.

c. Low-permeance sheets used as vapor retarders. High-permeance used elsewhere in construction.

d. Bases (weight in Ib/500 sq ft).

e. Permeability (perm, in)

f. Based on data from ASHRAE Handbook

Contributor:

Richard J. Vitullo, AIA, Oak Leaf Studio, Crownsville, Maryland

ESTIMATED PERMEANCE—WOOD

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Gypsum Board (3/8 in.)	50.0
Vapor retarder	0.06 (lowest permeance)
Insulation	29.0
Wood sheathing	2.9
4-in. brick veneer	1.1 (next lowest permeance)

In this example, the vapor barrier transmits one grain of moisture per square foot per hour for each unit of vapor pressure difference, or one perm; and nothing else transmits less. However, since the cold brick veneer is nearly as low in permeance, it is advisable to make certain that the vapor barrier is expertly installed, with all openings at pipes and with outlet boxes or joints carefully fitted or sealed. Alternatively, the brick veneer may have open mortar joints near the top and bottom to serve both as weep holes and as vapor release openings. They will also ventilate the wall and help reduce heat gain in summer.

ESTIMATED PERMEANCE—CMU

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Gypsum Board (3/8 in.) Furred space	50.0
8-in. CMU	2.4
4-in. brick veneer	1.1 (lowest permeance)

Vapor (under pressure) would easily pass through the interior gypsum board finish, be slowed by the concrete masonry unit, and be nearly stopped by the cold brick veneer. Unless this design is radically improved, the masonry will become saturated and, in cold weather, may cause serious water stains or apparent “leaks.” In addition, alternating freezing and thawing of condensation within the masonry wall can physically damage the construction.

These types of analysis are not appropriate for buildings in mixedclimate areas. For additional instructions see Chapter 11, “Design Tools,” by Anton TenWolde, in Moisture Control in Buildings, (ASTM Manual, No. 18) Heinz R. Trechsel (ed.), published by ASTM, 1984.

COMPUTERIZED ANALYSIS

The Figures 2.415 and 2.416 are simple graphical section analyses are limited in reliability. They are two-dimensional, and do not include issues such as thermal bridging at insulation in stud cavities.

Computerized modeling is recommended for large projects, assemblies that require seasonal drying, and for projects located in mixed climates. WUFI, by Oak Ridge National Laboratory (www.ornl.gov), is one strong and widely recognized modeling tool.

AIR LEAKAGE CONSEQUENCES

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AIR BARRIERS

An air barrier is a combination of interconnected materials, flexible sealed joints, and components of the building envelope that provide the airtightness of the building envelope. The main function of air barriers is to prevent unintentional air and moisture flow through the building enclosure. Leakage can affect the occupants’ comfort, as well as thermal performance and durability of the building.

BUILDING ENCLOSURE SEALING

The complete building envelope must be designed and constructed with a continuous air barrier to control air and moisture leakage into or out of the conditioned space. This includes the lowest-level slab-on-grade or crawl space surface, foundation walls, exterior walls, and roof.

Performance of the air barrier for the opaque envelope can be demonstrated by:

• Using individual materials that have an air permeance not to exceed 0.004 cfm/ft² under a pressure differential of 0.3 in. water gage (w.g.) (1.57 psf) when tested in accordance with ASTM E 2178.

• Using assemblies of materials and components that have an average air leakage not to exceed 0.04 cfm/ft² under a pressure differential of 0.3 in. w.g. (1.57 psf) when tested in accordance with ASTM E 1677.

• Testing the completed building and demonstrating that the air leakage rate of the building envelope does not exceed 0.40 cfm/sf at a pressure differential of 0.3 in. w.g. (1.57 psf) (2.0 L/s perm2 at 75 Pa) in accordance with ASTM E 779 or an equivalent approved method.

CHARACTERISTICS

The air barrier is required to have the following characteristics:

• Be continuous throughout the envelope (at the lowest floor, exterior walls, and ceiling or roof), with sealed connections between all transitions in planes and changes in materials, at all joints and seams, and at all penetrations.

• Be joined and sealed in a flexible manner to the air barrier component of adjacent assemblies, allowing for the relative movement of these assemblies and components.

• Be capable of withstanding positive and negative combined design wind, fan, and stack pressures on the air barrier without damage or displacement, and transfer the load to the structure. It must not displace adjacent materials under full load.

• Where lighting fixtures or other similar devices are to be installed in such a way as to penetrate the air barrier, provisions must be made to maintain the integrity of the barrier.

AIR BARRIER SYSTEMS

Many common building materials (concrete, plywood, roofing membranes, rigid insulation, and gypsum board) are capable of functioning as a weather barrier. For small-scale and residential construction, it is common to utilize either the sheathing or interior drywall as the weather barrier. Special sealing of these materials is required, but otherwise construction does not differ substantially from traditional frame construction. In commercial construction, the use of air barriers, applied over sheathing that fulfill the structural requirement is common. Common building materials that are not air barriers include CMU, board and blanket insulation (even if compressed), and polyethylene sheets.

AIR BARRIER MEMBRANES

Air barrier membranes are airtight materials specifically designed to control airflow through the building enclosure. The main types of air barrier membranes are summarized here. In addition to the primary membranes, air barrier systems must include installation and continuity accessories such as primers, mechanical fasteners, tapes, joint sealants, flashing, and transition membranes.

Based on the application method, air barrier membranes are classified into five categories:

• Self-adhered (or peel-and-stick) membranes are fabricated sheets consisting of rubber-modified asphalt bonded to a carrier film, and protected by release paper on the membrane side. These membranes are applied by self-adhesion to a dry, clean, and primed substrate. Self-adhered membranes are vapor-nonpermeable.

• Fluid-applied membranes are one- or two-component formulations in organic solvents or water dispersions, which are spray or trowel applied to a dry, clean, and primed substrate. Most fluid-applied membranes are vapor-nonpermeable. A few fluid-applied membranes are vapor-permeable, even though their permeability is quite low (<6 to 7 perms) and depend on the dry film thickness.

• Mechanically fastened membranes are, lightweight sheets installed typically with mechanical fasteners. Their installation does not require special surface preparation such as drying, priming, or taping of sheathing joints. Building wraps are vapor-permeable membranes, even though their vapor permeability varies widely depending on the membrane type and the manufacturer. The main types of building wraps are: (1) spunbonded polyolefins, (2) microporous films, (3) perforated films, and (4) asphalt-impregnated papers and felt. The seams and fasteners typically need to be taped or otherwise sealed.

• Torch-applied membranes are rubber-modified bitumen, laminated on a nonwoven substrate. The membrane is designed to be fused to a dry, clean, and primed substrate by heating the bitumen side with a propane torch. Torch-applied membranes are vapor-nonpermeable.

Contributors:

David F. Hill, Kosar, Rittolmann Associates, Buttler, Pennsylvania; Marc A. Giagceardo, College of Architecture, Texas Tech Universtiy, Lubbock, Texas; Maria Spinu, PhD, Dupont, Wilmington, Delaware.

• Sprayed polyurethane foams (SPF) are two-component foam membranes that combine thermal insulation and weather barrier properties. Only a few closed-cell SPF insulation foams have the required air infiltration resistance to qualify as air barriers.

Based on vapor permeability, air barrier membranes are classified into vapor-permeable and vapor-nonpermeable membranes (air barrier and vapor retarder). Building wraps and a few fluid-applied membranes are vapor-permeable though permeability varies widely among the different types. All other air barrier membranes described previously are vapor-nonpermeable.

Vapor permeability of the air barrier must be carefully considered when selecting a air barrier for the building enclosure.

• Vapor-permeable air barrier membranes can be placed anywhere in the wall assembly, based on ease of detailing. The membrane is often installed on the outer side of the exterior sheathing. In addition, there are no climate limitations for vapor-permeable air barriers. Air barriers can and should be used in all climates.

• Vapor-nonpermeable air barrier membranes generally must be located on the warm side of the wall assembly to avoid moisture accumulation. “The warm side of the wall assembly” is climatespecific. In the United States, with widely varying climates, it could be on different sides of the wall during different seasons. Consequently, the air barrier could end up on the cold side of the enclosure for part of the year, leading to moisture accumulation.

In summary, take into account the considerations listed in Table 2.367 when selecting an air barrier membrane.

AIR BARRIER CONSIDERATIONS

2.367

TYPE OF AIR BARRIER	LOCATION WITHIN BUILDING ENCLOSURE	CLIMATE CONSIDERATIONS AND LIMITATIONS
Vapor-permeable	Anywhere use	No climate limitations; in all climates
Vapor-nonpermeable (air barrier and vapor retarder)	Warm side	Consider climate to avoid condensation and moisture accumulation

When they are part of a drainage or pressure-equalized wall assembly, air barriers must also be resistant to the passage of water. Air barriers are crucial to the functioning of a pressure-equalized wall assembly. See Figure 2.368 for integration of flashings into these wall types.

The application of the flashing falls into two categories: through-wall flashing and flexible membrane flashing.

• Through-wall flashing must typically bridge the open air space and, therefore, is typically sheet metal. Stainless steel, aluminum, galvanized steel, and copper are most common.

• Flexible membrane flashing is used to bridge gaps, while allowing movement, and as a transition to other materials, assemblies, and systems. Flexible flashing can be self-adhered peel-and-stick membranes, but their use is limited to applications that do not require bridging a gap larger than 1/2 in. For larger gaps, and where more substantial movement is anticipated, neoprene sheets or extruded cured silicone sheets are common. Note that the membrane flashing sheets must be compatible with all of the adjacent materials they contact.

VAPOR RETARDERS

WATER VAPOR MIGRATION

Water is present as vapor in indoor and outdoor air and as absorbed moisture in many building materials. Within the range of temperatures encountered in buildings, water may exist in the liquid, vapor, or solid states. Moisture-related problems may arise from changes in moisture content, from the presence of excessive moisture, or from the effects of changes of state (such as freezing within walls, or deterioration of materials because of rotting or corrosion).

RAINSCREEN FLASHING

2.368

In the design and construction of the thermal envelope of buildings (the enclosure of desired temperatures and humidity ), the behavior of moisture must be considered, particularly the change of state from vapor to liquid (condensation). Problems arise when moisture comes into contact with a relatively cold surface (temperature below the dew point), such as a window, or within outdoor walls or under-roof/ceilings. Excessive condensation within indoor walls that enclose cold spaces must be considered.

Although vapor moves by vapor pressure differences, it is important to recognize that moisture moved in air will move much larger quantities of water. Consequently, the causes of air motion must be considered, especially the infiltration/exfiltration at undesirable leakage rates at windows, doors, and other penetrations through the thermal envelope of the building.

Moisture problems generally occur in seasons when the outdoor temperature and vapor pressure are low and there are many indoor vapor sources. These sources may be occupant-induced, such as cooking, laundering, bathing, breathing, and perspiration, or machine-induced, including automatic washers and dryers, dishwashers, and humidifiers. All of these sources combine to cause vapor pressure indoors to be much higher than outdoors, so that the vapor tends to migrate outward through the building envelope. Vapor cannot permeate glazed windows or metal doors, but many other building materials are permeable to some extent. Walls are particularly susceptible to this phenomenon and such migration must be prevented, or at least minimized, by the use of low-permeance membranes, called vapor retarders. A vapor retarder is a material that has a flow rating of one perm or less (1 perm = 1 grain/hr ft-in. Hg vapor pressure difference).

Vapor barriers, when installed along with properly treated joints and penetrations, form a vapor retarder assembly, though it does not stop all vapor transmission. Vapor retarder assemblies should be installed as close as possible to the side of the wall through which moisture enters. Therefore, it is important to establish the side of moisture entrance in walls of controlled rooms within buildings. Also note that the beneficial effects of good vapor retarders will be lost without adequate weather barriers.

Moisture in building materials usually increases their thermal conductance significantly and unpredictably. Porous materials that become saturated with moisture lose most of their insulating capability and may not regain it when they dry out. Dust, which usually settles in airspaces, may become permanently affixed to originally reflective surfaces. Moisture migration by evaporation, vapor flow, and condensation can transport significant quantities of latent heat, particularly through fibrous insulating materials.

Positive steps should be taken to prevent migration of moisture in the form of vapor, and accumulation in the form of water or ice within building components. Vapor retarders, correctly located near the source of the moisture, are an effective means of preventing such migration. Venting of moisture-laden air from bathrooms, laundry rooms, and kitchens will reduce indoor vapor pressure, as will the introduction of outdoor air with low moisture content.

PARAPETS, COPINGS, AND GRAVEL STOPS

Parapets, copings, and gravel stops are problematic areas. Roofing and wall assemblies come together at an area that also experiences large amounts of thermal and structural movement. Detailing for long-term performance must be carefully considered to address each issue.

PARAPETS

Parapets experience many problems, as indicated in Figure 2.420. However, parapets do provide safety to rooftop maintenance personnel, allow for sloping roof structures without showing the slope on the elevation, and allow for the most dependable detailing of the interface with the roof system. The wall assembly weather barrier must connect to the roofing assembly.

PARAPET PROBLEMS

2.369

The structural system of the wall (typically CMU or stud framing) must cantilever past the roof to support the parapet against high wind loads. Two common options include allowing the wall structure to continue from a lower level past the roof framing (balloon frame), or, cantilevering off the roof framing with a rigid moment-resisting connection. When tall parapets are required in wood or CFS construction, it is best to use the balloon frame method.

Detail membranes and closed-cell spray-applied foam to control air leaks and thermal bridging through parapets. Ensure that steel members that penetrate to parapet will not reach dew point within interior environment.

The structure for very short parapets may be included within the HAM enclosure, but because of limited air circulation, framing members more than 12 in. above the roof in cold climates will fall below the dew point because of the exposure to the exterior on three sides.

Contributor:

Maria Spinu, PhD, DuPont, Wilmington, Delaware.

GENERIC PARAPETS

2.370

PARAPET CAP SPLICE JOINT

2.371

COPINGS

Copings are small roof areas and, as such, joints in sheet metal or masonry copings are not sufficiently reliable. Provide a waterproof backup of the air/vapor barrier, the roof base flashing, or a layer of membrane flashing.

Coping materials are commonly sheet metal, cast stone, and cut stone. Metals can have inherent finishes such as zinc, copper, and galvanized steel or aluminum; or steel with an applied finish that includes anodized, color-anodized, polyvinylidene fluoride (Kynar), baked-on enamels, powder coatings, and many others. PVDF coatings have become very common because of their wide range of colors and metallic finishes, extreme durability, and color consistency.

EDGE DETAIL

2.372

Sheet metal copings can be formed at a local shop or be a standard manufactured system. Manufactured copings provide improved appearance and engineered wind performance, whereas shop-fabricated copings are easier to obtain for small jobs or to customize.

GRAVEL STOPS

Gravel stops terminate the roof edge and cover the top of the wall. In rainscreen walls, the gravel stop covers the top of the air space and provides venting. The air barrier/vapor retarder membrane must be sealed to the roofing assembly under the gravel stop.

Gravel stops are available shop-made or manufactured in the same materials as metal copings.

They must be sealed into the roofing membrane, but the two systems have different coefficients of thermal expansion. Shop-fabricated gravel stop is nailed in two rows at 3 in. o.c to restrict the movement of the metal. Manufactured systems either anchor the system in a similar method or use spring metal systems to allow differential movement.

GRAVEL STOP

2.373

Contributor:

Joseph J. Williams, AIA, A/R/C/ Associates, Inc., Orlando, Florida.

GRAVEL STOP SPLICE JOINT

2.374

GRAVEL STOP OUTSIDE CORNER FABRICATION

2.375

EXTERIOR WINDOWS

Although architects choose fenestration products based on many unique priorities and circumstances, a number of common considerations apply to most situations. Here are the factors that affect window choice:

• Appearance: Size and shape, operating type and style, frame materials, glass color and clarity

• Function: Visible light transmittance (provision of daylight), glare control, reduction in fading from ultraviolet radiation, thermal comfort, resistance to condensation, ventilation, sound control, maintenance, and durability

• Energy performance: U-value, solar heat gain coefficient (SHGC) (which is replacing the shading coefficient), air leakage, annual heating and cooling season performance, and peak load impacts

• Cost: Initial cost of window units and installation, maintenance and replacement costs, effect on heating and cooling plant costs, and cost of annual heating and cooling energy

Many designers and homeowners find it difficult to assess the value of choosing a more energy-efficient window. Although some basic thermal and optical properties (e.g., U-factor, solar heat gain coefficient, and air leakage rate) can be identified if a window is properly labeled, this information does not tell how these properties influence annual energy use for heating and cooling. This must be determined by using an annual energy rating system or by computer simulation.

WINDOW CONFIGURATIONS

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WINDOW BASICS

Any discussion on exterior windows must begin by defining these key terms:

• Borrowed light: An interior wall opening or window that allows light to be transferred into another space.

• Clerestory: The portion of a wall above an adjacent roof level; also, a fixed or operable window located in this part of a wall.

• Dormer: A vertical window set above the line of a sloped roof in a small projecting space with triangular side walls.

• Internal dormer: A vertical window set below the line of a sloped roof.

• Oriel window: A bay window supported by brackets, corbeling, or cantilevers.

• Window wall: A continuous series of fixed or operable sashes, separated by mullions that form an entire nonload-bearing wall surface.

• Ribbon window: A horizontal band of fixed or operable windows extending across a significant portion of the façade.

• Mullion: A slender vertical member separating lights, sashes, windows, or doors.

• Muntin: Nonstructural members separating panes within a sash; also called a glazing bar or sash bar.

• Sash: The basic unit of a window, consisting of frame, glazing, and gasketing; may be stationary or operable.

Contributors:

Joseph J. Williams, AIA, A/R/C/ Associates, Inc., Orlando, Florida; Richard J. Vitullo, AIA, Oak Leaf Studio, Crownsville, Maryland; John Carmody, University of Minnesota, Minneapolis, Minnesota; Stephen Selkowitz, Lawrence Berkeley National Laboratory, Berkeley, California.

PARTS OF A WINDOW

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PERFORMANCE

Performance standards can be divided in three categories:

• Structural, air filtration, and water leakage

• Thermal and condensation

• Specialized

STRUCTURAL, AIR INFILTRATION, AND WATER LEAKAGE PERFORMANCE

These elements are standardized through ANSI/AAMA/WDMA 101/I.S. 2-97, “Voluntary Performance Specifications for Windows, Skylights, and Glass Doors.” The 101 specification establishes five classes for windows and doors: R, LC, C, HC, and AW (i.e., residential, light commercial, commercial, heavy commercial, and architectural, respectively). This specification was updated in 2002 and 2005. In brief, the specification says:

• Select the class based on the project. The class titles are somewhat self-explanatory, but not limiting. AW class windows are typically used for institutional type projects, but they can also be used on a very high-quality house, for example.

• Performance is designated by a number that follows the type and class. For example, “DH-AW 40” designates a double-hung architectural window with a design pressure of 40 psf.

• The number is based on the anticipated structural wind load acting on the window, as determined from ASCE 7 and as required by the building code. Each type and class has minimum performance grades; optional grades increase in 5 psf increments.

• The designation is based on testing of samples for structural performance, air infiltration, and water leakage according to standardized methods. The higher the class, the more difficult the test.

• Windows can be selected of various grades to suit the field pressure and higher wind pressures at corners and higher elevations, or the windows for the entire building can be based on the highest wind pressure.

The 101 specification also provides standards for durability, operating forces, safety, materials, hardware, and overall quality.

Note that the ratings are based on specific test sizes, so it is necessary to verify that the tested size is at least as large as the windows required for the project. Also note that the tested window rarely includes perimeter pan flashing, receivers, mulled assemblies, or other nonstandard configurations, so it’s important to ask the manufacturer how these conditions affect performance.

THERMAL AND CONDENSATION PERFORMANCE

Specific exterior climate and desired interior conditions affect the thermal performance of windows the most. Carefully evaluate these conditions to determine acceptable performance criteria, and then select windows that meet the criteria.

• Thermal performance of windows is rated according to NFRC 100, through standardized tests of windows. Note that glazing can dramatically affect the thermal performance, so verify the glazing used in the test versus project requirements.

• Condensation resistance is determined by AAMA test 1503.1; the higher the number, the better the performance. CRF (condensation resistance factor) testing is performed on standardsized samples and includes glazing, which can influence the results. Note that the CRF test averages out a large number of temperature readings, meaning that a high-reported value may still include areas that perform relatively poorly. If absolutely no condensation is acceptable, then greater scrutiny of the actual test data versus the final CRF value is recommended.

• Assuming frames have thermally resistive materials or have thermal breaks, the glazing may be the major determinant of CRF and overall thermal performance. See the “Condensation Potential” chart, Figure 2.398.

• Thermal and CRF performance affect not only energy usage but also occupant comfort. Analyze the area of glazing, the location and activity of the occupant, and the use of supplemental heating for adequate protection.

SPECIALIZED PERFORMANCE

Standardized test procedures are available to evaluate a great many specialized performance criteria, including acoustic isolation, blast resistance, forced-entry resistance, and safety impact. Refer to the AAMA.

DETAILING

Manufacturers of windows provide only generic details for installation. Adjacent construction is frequently shown as a hatched single line. Therefore, it is necessary to detail the window frame in project-specific assemblies.

WALL ASSEMBLIES

Window installation must be detailed as appropriate for the generic wall assembly type, as described below.

• Barrier walls: Seal the window to the barrier. Use a subsill flashing to avoid introducing water into the wall. For massive barrier walls such as precast concrete, head flashing may be required to ensure that water seepage does not get behind the window.

• Drainage plane walls: Provide the primary seal of the window to the water-resistant drainage plane, and an outer seal in line with the wallcovering. The subsill flashing should extend past the outer wallcovering.

• Drainage cavity walls: Provide the primary seal of the window to the waterproof inner line of protection and an outer seal to the outer wallcovering. The subsill flashing may be detailed to weep into the drainage cavity because only incidental water should leak around the window.

• Pressure-equalized (PE) rainscreen walls: Use windows that incorporate PE rainscreen technology. Seal the air barrier of the window to the wall air barrier; likewise for the rainscreen. The subsill flashing may be detailed to seal to the air barrier.

AIR AND VAPOR BARRIERS

Detail the window installation so that the line of the air barrier and/or vapor barrier (if required) extends uninterrupted across the gap at the perimeter of the window. In windows with glass installed using wiggle glazing, or if interior removable stops are used, a heel bead may be required to maintain continuity of the air barrier between the frame and glass.

MOVEMENT

Window installation details must accommodate movement of the surrounding structure. Window heads (particularly at strip windows) often are located at shelf angles, and must accommodate movement typically in the range of 1/2 in. from above.

THERMAL CONTINUITY

Detail the windows to maintain a line of thermal insulation in the same plane as in the tested configuration and as intended by the window manufacturer. Windows installed over an air space in a drainage cavity wall may be exposed to cold on sides for which proper thermal breaks are not provided.

ADDITIONAL INFORMATION

For more information, see the AAMA Window Selection Guide.

Contributors:

John Carmody, University of Minnesota, Minneapolis, Minnesota; Stephen Selkowitz, Lawrence Berkeley National Laboratory, Berkeley, California.

WINDOW OPERATION TYPES

Accessibility issues for windows are important for present and future occupants. See Beautiful Universal Design: A Visual Guide (John Wiley & Sons, Hoboken, NJ), by Cynthia Leibrock and James Evan Terry for a complete discussion.

WINDOW OPERATION TYPES

2.378

CHARACTERISTICS OF WINDOW OPERATION TYPES

2.379

Contributors:

John Carmody, University of Minnesota, Minneapolis, Minnesota; Stephen Selkowitz, Lawrence Berkeley National Laboratory, Berkeley, California; Daniel F.C. Hayes, AIA, Washington, DC.

GLASS PRODUCTS

Glass is a hard, brittle, amorphous substance made by melting silica (sometimes combined with oxides of boron or phosphorus) with certain basic oxides (notably sodium, potassium, calcium, magnesium, and lead) to produce annealed flat glass by a controlled cooling process. Most glasses soften at 932°F to 2012°F (500°C to 1100°C). The brittleness of glass is such that minute surface scratches in manufacturing greatly reduce its strength.

INDUSTRY-QUALITY STANDARDS

A number of industry-quality standards apply to glass products:

• Glazing Association of North America (GANA) Glazing Manual

• ASTM C 1036: “Specification for Flat Glass”

• ASTM C 1048: “Specification for Heat-treated Flat Glass—Kind HS, Kind FT Coated and Uncoated”

• UL Standard 752: Bullet-Resisting Equipment

• UL Standard 752: Bullet-Resisting Glazing Material

• AAMA Curtain Wall and Storefront Publications: Glass and Glazing

• ASTM E 1300: “Practice for Determining Load Resistance of Glass in Buildings”

• CPSC Standard 16CFR 1201: Safety Standard for Architectural Glazing Materials

• ANSI Z97.1: Safety Glazing Materials Used in Buildings—Safety Performance Specification and Methods of Test

• ASTM C 1172: “Specification for Laminated Architectural Flat Glass”

More information can also be found in these two books: Glass in Building by David Button and Brian Pye (Pilkington, with Butterworth Architecture, 1993) and Glass in Architecture by Michael Wiggington (Phaidon Press Ltd., 1996). Also, be sure to consult glass manufacturers for current information because processes, qualities, finishes, colors, sizes, thicknesses, and limitations are revised continually. The information presented here represents one or more manufacturers’ guidelines.

BASIC TYPES OF CLEAR GLASS

The following are basic types of clear glass:

• Sheet glass: Sheet glass is manufactured by a horizontal flat or vertical draw process, and then annealed slowly to produce a natural flat-fired, high-gloss surface. It generally is used in residential and industrial applications. Because it is not mechanically polished, inherent surface waves are noticeable in sizes larger than 4 sq ft. For minimum distortion, larger sizes are installed with the wave running horizontally. The width is listed first when specifying. For architectural applications, sheet glass is either single-strength (0.101 in. thick) or double-strength (0.134 in. thick). Very little glass is produced in the United States by this process; almost all sheet glass is produced by the float process.

• Float glass: Generally accepted as the successor to polished plate glass, float glass has become the quality standard of the glass industry. It is manufactured by floating molten glass on a surface of molten tin, then annealing it slowly to produce a transparent flat glass, thus eliminating grinding and polishing. This process produces a glass with very uniform thickness and flatness, making it suitable for applications requiring excellent optical properties, such as architectural windows, mirrors, and specialty applications. It is available in thicknesses ranging from 1/8 to 7/8 in.. Float glass is made to the specification requirements of ASTM C 1036, and its minimum thickness to resist wind load is established using ASTM E 1300.

• Plate glass: Transparent flat glass is ground and polished after rolling to make plate glass. Cylindrical and conical shapes can be bent to a desired curvature (within limits). Only glass for specialty applications is produced by this method; it is not produced for widespread use in architectural applications.

VARIATIONS OF BASIC GLASS TYPES

Several variations of the basic glass types are in use today.

• Patterned glass: Patterned glass is known also as rolled or figured glass. It is made by passing molten glass through rollers that are etched to produce the design. Designs include flutes, ribs, grids, and other regular and random patterns, which provide translucency and a degree of obscurity. Usually, only one side of the glass is imprinted with a pattern. Patterned glass is available in thicknesses of 1/8, 3/16, and 7/32 in.

• Wire glass: Wire glass is available as clear polished glass or in various patterns such as square-welded mesh, diamond-welded mesh, and linear parallel wires. Some distortion, wire discoloration, and misalignment are inherent. Some 1/4-in. wired glass products are recognized as certified safety glazing materials for use in hazardous locations (e.g., fire-rated windows, doors, and skylights). For applicable fire and safety codes that govern their use, refer to ANSI Z97.1. Note that wire glass is no longer exempt from regulations for locations requiring safety glass (i.e., doors and sidelights). Therefore, it is better to avoid wire glass entirely. Consider using other laminated and specialty fire-rated and safety-rated products. If wire glass must be used, ensure that the submitted product complies with the indicated requirement for special wire glass that does comply with safety regulations. Verify application of patterned wire glass to avoid applications requiring safety glazing.

• Cathedral glass: Cathedral glass is known also as art glass, stained glass, or opalescent glass. It is produced in many colors, textures, and patterns. Cathedral glass is usually 1/8 in. thick, and is used primarily in decorating leaded glass windows. Specialty firms usually contract this type of glass.

• Obscure glass: Obscure glass is used to obscure a view or create a design. The entire surface on one or both sides of the glass can be sandblasted, acid-etched, or both. When a glass surface is altered by any of these methods, the glass is weakened, and may be difficult to clean.

STRENGTHENED GLASS

Glass can be strengthened either by a controlled heating and cooling process, or by immersion in a chemical bath. Both processes have glass thickness, size, and use restrictions that should be verified.

HEAT-TREATED GLASS

Heat-strengthened (Kind HS) and tempered (Kind FT) glass are produced by reheating annealed float glass close to its softening point and then rapidly quenching (cooling) it with high-velocity blasts of air. Both types have greatly increased mechanical strength and resistance to thermal stresses. Before it is heat-treated, the glass must be fabricated to its exact size and shape (including any holes), because neither type of glass can be altered after heat treatment.

Most manufacturers heat-treat the glass using a horizontal process that can introduce warpage, kinks, and bowing into the finished product, which may create aesthetic or technical concerns. A vertical process may still be available that produces tong marks or depressions into the glass surface near the suspended edge. Vertical processing may produce large amounts of warping and distortion. The heat treatment quenching pattern on the surface of the glass can become visible as a pattern of light and dark areas at certain oblique viewing angles and with polarized light. This effect can be more pronounced with thicker glass and may be an aesthetic consideration. Refer to ASTM C 1048 for allowable tolerances and other properties.

Heat-strengthened glass is generally two to three times stronger than annealed glass. It cannot be cut, drilled, or altered after fabrication. Unlike tempered glass, it breaks into large, sharp shards similar to broken annealed glass. Heat-strengthened glass is not acceptable for safety glazing applications.

TEMPERED GLASS

Tempered glass is generally four to five times stronger than annealed glass. It breaks into innumerable small, cube-shaped fragments. It cannot be cut, drilled, or altered after fabrication; the precise size required and any special features (such as notches, holes, edge treatments, and so on) must be specified when ordering.

Tempered glass can be used as a safety-glazing material provided it complies with the ANSI and CPSC references listed in the “Laminated Glass” section, below. Tempered glass can be used in insulating and laminated assemblies and in wired, patterned, and coated processes. All float and sheet glass 1/8 in. or thicker may be tempered.

CHEMICALLY TREATED GLASS

Chemically treated glass is produced by submerging annealed float glass in a bath of molten potassium salts. The larger potassium ions in the bath exchange places with the smaller sodium ions in the glass surface, creating a surface compression layer that strengthens the glass. Chemically treated glass breaks into large, sharp shards similar to broken annealed glass. It does not have the visual distortion that can be caused by a heat-treated strengthening process. At present, chemical strengthening is primarily limited to the glass lights of laminated security glass.

ULTRACLEAR GLASS

The high clarity and high visible light transmittance that characterize ultraclear glass comes from the special soda lime mixture it is made from, which minimizes the iron content that normally gives a slight greenish color to clear flat glass. Ultraclear glass is generally available in thicknesses from 1/8 to 3/4 in. It can be heat-strengthened, tempered, sandblasted, etched, or assembled into laminated glass. Ultraclear glass is used for commercial display cases, museum cases, display windows, frit-coated spandrel glass, aquariums, mirrors, shelving, security glass, and other uses in which clarity and better color transmittance are required.

HEAT-ABSORBING OR TINTED GLASS

This type of float glass was developed to help control solar heat and glare in large areas of glass. It is available in blue, bronze, gray, or green, and in thicknesses ranging from 1/8 to 1/2 in. The glass absorbs a portion of the sun’s energy because of its admixture contents and thickness; it then dissipates the heat to both the exterior and interior. The exterior glass surface rejects some heat, depending on the sun’s position. Heat-absorbing glass has a higher temperature than clear glass when exposed to the sun; thus, the central area expands more than the cooler, shaded edges, causing edge tensile stress buildup. When designing heat-absorbing or tinted glass windows, consider the following:

SOLAR PERFORMANCE OF HEAT-ABSORBING OR TINTED GLASS

2.380

Contributor:

Thomas F. O’Connor, AIA, FASTM, Smith, Hinchman & Grylls, Detroit, Michigan.

• To minimize shading problems and tensile stress buildup at the edges, provide conditions in which glass edges warm as rapidly as the exposed glass.

• The thicker the glass, the greater the solar energy absorption.

• Indoor shading devices such as blinds and draperies reflect energy back through the glass, thus increasing the temperature of the glass. Spaces between indoor shading devices and the glass, including ceiling pockets, should be vented adequately. Heating elements always should be located on the interior side of shading devices, directing warm air away from the glass.

• The glass can be heat-treated to increase its strength and resistance to edge tensile stress buildup.

INSULATING GLASS

Insulated glass is constructed from two or more panes of glass separated by spacer bars to form a hermetically sealed void between the panes. This arrangement greatly enhances the insulating thermal and acoustic properties of the glass unit. The most common insulated units are filled with air, and employ a hollow spacer bar containing a desiccant to absorb moisture vapor inside the unit. The void can be filled with an inert gas such as argon, and the spacer can be changed to a “warm edge” type to further improve the insulating value of the unit. The spacer bar is sealed to the glass with a continuous joint sealant (typically, butyl or silicone) forming an airtight seal. Structural joint sealant, usually silicone or polyurethane, is applied outboard of the spacer bar to hold the panes of glass together, especially during transport and handling. For coastal environments, in structural silicone glazing systems and when otherwise recommended by the manufacturer, the architect may limit both sealants to silicone type. By varying the makeup of the individual panes of glass in the insulating unit, its insulating, shading and visual characteristics can be greatly enhanced.

Durability for insulating glass is established through ASTM E 774, “Standard Specification for the Durability of Sealed Insulated Glass Units,” for Class C, CB, or CBA. Class CBA is the most durable and is typically selected for most commercial and institutional work.

SOUND CONTROL GLASS

Laminated, insulating, laminated insulating, and double laminatedinsulating glass products commonly are used for sound control. STC ratings from 31 to 51 are available, depending on glass thicknesses, airspace size, polyvinyl butyral film thickness, and number of laminated units used in insulating products.

SPANDREL GLASS

Spandrel glass is available tinted or with a variety of coatings, including reflective, ceramic frit (patterned and solid colors), and direct-to-glass polyvinylidene fluoride (PVDF) coatings. It can be heat-treated or laminated, and is available as insulating glass units. Insulation and vapor retarders can be added to spandrel glass. Consult with spandrel glass manufacturers for guidelines.

SECURITY GLASS

Security glass is composed of multiple layers of glass and/or polycarbonate plastic that are laminated together under heat and pressure with a polyvinyl butyral (for glass) or polyurethane plastic (for polycarbonate) film. It is available in multilayer laminated glass, insulating, laminated insulating, and double-laminated insulating or spaced configurations, generally in thicknesses from 3/8 in. to 2-1 /2 in. as a laminated product and up to about 4-1/4 inches for insulating and spaced construction products. Bullet-resistant glass should be tested to UL 752, and burglar-resistant to UL 972. Consult manufacturers for blast-resistant glass. Security glass products, depending on type, are subject to size limitations, and some are not recommended for exterior applications. Consult with the manufacturer for glazing requirements and restrictions on use.

TYPICAL INSULATING OR SPACED CONSTRUCTION SECURITY GLASS PROFILE

2.381

TYPICAL MULTILAYER SECURITY GLASS PROFILE

2.382

COATED GLASS

A reflective or low-emissivity coating can be applied to the surface of monolithic glass. Generally, only pyrolitically applied “hard” coatings (which have scratch resistance) are used on exposed glass surfaces. During glass manufacture, pyrolitic coatings are sprayed onto the glass before it cools, which integrates them with the glass surface. Magnetically sputtered or “soft” coatings can also be applied to the glass surface, but they must be protected from the elements as part of an insulating or laminated glass product. The range of coating types, aesthetic appearances, and thermal performance available for pyrolitic coatings is generally less than for sputtered coatings.

LAMINATED GLASS

To produce laminated glass, a tough, clear plastic polyvinyl butyral (PVB) sheet (interlayered), ranging in thickness from 0.015 to 0.090 in., is sandwiched, under heat and pressure, between lights of sheet, plate, float, wired, heat-absorbing, tinted, reflective, low-emissivity, or heat-treated glass, or combinations of each. When laminated glass breaks, the particles tend to adhere to the plastic film.

Laminated glass is manufactured to the specification requirements of ASTM C 1172. Laminated safety glass should be manufactured to comply with ANSI Z97.1 and CPSC 16CFR 1201.

LAMINATED GLASS PROFILE

2.383

BENT GLASS

Clear, tinted, ceramic frit-coated spandrel, pyrolitically coated, patterned, laminated, and wire glass are among glass types that can be bent in thicknesses to about 1 in. and to a minimum radius of about 4 in. Sharp angle bends to 90˚, edgework, pattern cutting, and tempering (meeting safety glazing standards), and heatstrengthening are also available. Bent glass can be fabricated into insulating glass units. Bent glass tolerances must be compatible with the glazing system. Size, configuration, and product availability vary by fabricator.

PHOTOVOLTAIC (PV) GLASS

There are two types of photovoltaic (PV) glass: crystalline silicon (sandwiched between two lights of glass) and thin-film amorphous silicon (applied to an interior-facing glass surface). When these arrangements are exposed to sunlight, they generate either DC or AC power, which is transferred by concealed wiring to the building’s power system. Pressure bar or structural silicone flush-glazed curtain walls and skylights, awnings, sunshades, light shelves, and roof panels are some of the systems that can incorporate PV glass. For curtain walls and skylights, the pressure bar type allows easy concealment of the wiring. Shadow patterns from the cap on the PV glass surface must be considered in system design. Flush-glazed systems have no shadow patterns, but wiring concealment is more difficult, and the PV module on the glass must be kept from reacting with the structural silicone sealant. Both types of PV glass are used for opaque curtain wall spandrel panels and can be used for curtain wall or skylight vision glass if the quality of daylighting and visibility is acceptable. Consult PV glass and metal-framing system manufacturers to determine availability, suitability, and cost for a particular application.

Contributors:

Thomas F. O’Connor, AIA, FASTM, Smith, Hinchman and Grylis, Detroit, Michigan.

PHOTOVOLTAIC GLASS (IN A PRESSURE BAR FRAMING SYSTEM)

2.384

DECORATIVE SILK-SCREENED (OR FRIT) GLASS

Annealed clear or tinted glass is washed and ceramic frit paint (in standard or custom color) silk-screened on its surface in a standard or custom pattern or design (such as dots, holes, lines, or a logo) and then dried in an oven. The frit-coated glass is then subjected to very high temperatures in a tempering furnace to fire the ceramic frit permanently to the glass surface. As a result, silk-screened glass will be either heat-strengthened or tempered after firing. Reflective and low-emissivity coatings can also be applied to the glass surface. Silk-screened glass can be used monolithically or for insulating or laminated glass products.

LEADED STAINED GLASS

Decorative stained glass is characterized by pieces of glass joined together with cames (H-shaped strips) of various widths. Varying the widths adds to the window’s decorative effect. Joints are soldered on both sides of the panel. To prevent leakage, a mastic waterproofing material is inserted between the glass and came flange.

Another method of joining the pieces of glass is to band the edges of the glass with a copper foil tape, burnished to the glass and then soldered with a continuous bead of solder on both sides.

Bracing bars are fastened to the sash at frequent intervals to strengthen and support the leaded glass. Round bars tied to the leaded glass with twisted copper wires are the most flexible and resilient, allowing for great amounts of thermal movement. Where this system is not suitable, galvanized steel flat bars can be soldered to the surface of the leaded glass.

When the glass requires detail painting, shading, or texturing, it must be done with special mineral pigments and fired at temperatures of 1000°F to 1200°F or higher to ensure absolute permanency.

OUTSIDE PROTECTION GLASS

Properly made decorative glass does not necessarily need additional glazing to make it waterproof, but it is valuable for insulating purposes and to afford some protection from external damage. Frames should be designed with a 3/4-in. ventilated space between glass, and should be arranged for the protection glass to be installed from the exterior, and the decorative glass from the interior. Clear glass or textured glass 3/16 to 1/4 in. thick is most successful.

GLAZING SEALANTS

Exterior decorative glass must be pressed into a deep back bed of mastic compound or glazing tape. When outside protection glass is used, a watertight seal is not required, and foam tape compressed between the glazing bead and glass may suffice.

SIZE LIMITATIONS

Decorative glass panels should not exceed 12 sq ft, making it necessary to divide larger openings with metal division bars: tee bars for single glazed windows, and special channel bars for windows with outside protection glass.

GLASS COLORS

Machine-made and blown glass from the United States, England, France, and Germany are available in most solid colors, as wells as mixed colors and textures. Uniformity of color will vary from glass of different batches. Special colors are derived by “sumping,” or kiln firing.

FACETED STAINED GLASS

A twentieth-century development in the art of stained glass introduced the use of glass dalles, 8 by 12 by 1 in., cast in hundreds of different colors. These can be cut to any shape and used in combination with an opaque matrix of epoxy resin or reinforced concrete 5/8 to 1 in. in thickness, to create translucent windows and walls of great beauty. Sizes are limited, and an outer protection glass is required.

Further information is available from the Stained Glass Association of America.

AVERAGE PERFORMANCE VALUES OF 1/4-IN. UNCOATED GLASS

2.385

DECORATIVE GLASS PANELS

2.386

FACETED STAINED GLASS

2.387

WINDOW GLAZING

Important window glazing considerations are as follows:

• Dry glazing methods are generally less expensive than wet methods.

• Cap beads make glazing watertight and weathertight and are required for face-sealed glazing systems. Cap beads can also be used to increase the performance of existing windows.

• Pressure-plate glazing systems are common for many site-fabricated curtain wall systems.

• Four-sided structural silicone work is generally required to be shop fabricated.

• Two-sided structural silicone glazing usually has the other two sides either pressure-plate glazed or wet/dry glazed.

• Heel beads can be added at the bottom edge and turned up 6 to 8 in. to protect against water leaks caused by differential pressures between the interior and exterior.

• Heel beads at the full perimeter may be required to provide a continuous air barrier in a pressure-equalized rainscreen curtain wall system.

Contributors:

Thomas F. O’Connor, AIA, FASTM, Smith, Hinchman & Grylls, Detroit, Michigan; Randall S. Lindstrom, AIA, Ware Associates, Inc., Chicago, Illinois; Joseph A. Wilkes, FAIA, Annapolis, Maryland; Bobbie Burnett Studio, Annapolis, Maryland.

• Skylights generally use wet glazing methods, cap beads, or structural silicone glazing.

• “Wiggle” or “jiggle” glazed systems use dry glazing with a removable stop along only one side of the frame or sash. After installing the outer line of gaskets, the pane of glass is wiggled into oversized glazing pockets, the removable stop is installed, and the inner gaskets are installed.

WET GLAZING

2.388

INSULATING GLASS IN WOOD SASH

2.389

BUTT JOINT GLAZING

2.390

DRY GLAZING

2.391

PRESSURE-GLAZED SYSTEM

2.392

STRUCTURAL SILICONE GLAZING

2.393

WET/DRY GLAZING SYSTEM

2.394

WET/DRY GLAZING WITH CAP BEAD

2.395

STRUCTURAL SILICONE GLAZING—TYPICAL VERTICAL MULLION FOR TWO-SIDED SYSTEM

2.396

Butt-joint glazing generally is not acceptable for insulating glass unless a careful review has been conducted in concert with the manufacturer of the insulating unit, because excessive deflection of unsupported edge may cause premature failure.

STRUCTURAL SILICONE GLAZING—TYPICAL HORIZONTAL MULLION FOR FOUR-SIDED SYSTEM

2.397

CONDENSATION POTENTIAL

Figure 2.484 shows the potential for condensation on glazing (at the center of glass) at various outdoor temperatures and indoor relative humidity conditions. Condensation can occur at any point on or above the curves. (Note: All airspaces are 1/2 in.; all coatings are E = 0.10.)

For example, at 20˚F outside, condensation will form on the inner surface of double glazing when the indoor relative humidity is 52 percent or higher. It will form at an indoor relative humidity of 70 percent or higher if a double-pane window with a low-E coating and argon fill is used.

CONDITIONS THAT LEAD TO CONDENSATION ON WINDOWS

2.398

THERMAL RESISTANCE VALUES OF GLAZING MATERIALS

The thermal conductivity of glass is relatively high (k = 7.5); and for single glazing, most of the thermal resistance is imposed at the indoor and outdoor surfaces. Indoors, approximately two-thirds of the heat flows by radiation to the room surfaces; only one-third flows by convection. This can be materially affected by the use of forced airflow from induction units, for example. The inner surface coefficient of heat transfer, hi, can be substantially reduced by applying a low-emittance metallic film to the glass.

For glazing with airspaces, the U-value can be reduced to a marked degree by the use of low-emittance films. This process imparts a variable degree of reflectance to the glass, thereby reducing its shading coefficient.

Manufacturers’ literature should be consulted for more details on this important subject. Also consult the ASHRAE Handbook.

SOLAR GAIN THROUGH FENESTRATION SYSTEMS

Heat gains through sunlit fenestration constitute major sources of cooling load in summer. In winter, discomfort is often caused by excessive amounts of solar radiation entering through south-facing windows. By contrast, passive solar design depends largely on admission and storage of the radiant energy falling on south-facing and horizontal surfaces. Admission takes place both by transmission through glazing and by inward flow of absorbed energy. With or without the sun, heat flows through glazing, either inwardly or outwardly, whenever there is a temperature difference between the indoor and outdoor air. These heat flows may be calculated in the following manner.

The solar heat gain is estimated by a two-step process. The first step is to find, either from tabulated data or by calculation, the rate at which solar heat would be admitted under the designated conditions through a single square foot of double strength (1/8-in.) clear sheet glass. This quantity, called the solar heat gain factor (SHGF), is set by (a) the local latitude; (b) the date, hence the declination ; (c) the time of day (solar time should be used); (d) the orientation of the window. Tabulated values of SHGF are given in the ASHRAE Handbook, for latitudes from 0° (the equator) to 64° N by 8° increments and for orientations around the compass from N to NNW, by 22.5° increments. Selected values from the 40° table are given in an adjacent column.

Each individual fenestration system, consisting of glazing and shading devices, has a unique capability to admit solar heat. This property is evaluated in terms of its shading coefficient (SC), which is the ratio of the amount of solar heat admitted by the system under consideration to the solar heat gain factor for the same conditions.

In equation form, this becomes:

Solar heat gain (Btu/sq ft • hr) = SC × SHGF

Values of the shading coefficient also are given in the ASHRAE Handbook for the most widely used glazing materials alone and in combination with internal and external shading devices.

GLASS THERMAL RESISTANCE VALUES

2.399

NOTES

2.399 a. Resistances are representative values for dry materials and are intended as design (not specification) values for materials in normal use. Unless shown otherwise in descriptions of materials, all values are for 167°F mean temperature.

b. Includes paper backing and facing, if any. In cases where insulation forms a boundary (highly reflective or otherwise) of an airspace, refer to the appropriate table for the insulating value of the airspace. Some manufacturers of batt and blanket insulation mark their products with an R-value, but they can ensure only the quality of the material as shipped.

c. Average values only are given, as variations depend on density of the board and on the type, size, and depth of perforations.

d. Thicknesses supplied by different manufacturers may vary, depending on the particular material.

e. Values will vary if density varies from that listed.

f. Data on rectangular core concrete blocks differ from the data for oval core blocks because of core configuration, different mean temperature, and different unit weight. Weight data on oval core blocks are not available.

g. Weight of units approximately 75/a high by 155/s long are given to describe blocks tested. Values are for 1 sq ft area.

h. Thermal resistance of metals is so low that in building constructions it is usually ignored. Values shown emphasize relatively easy flow of heat along or through metals so that they are usually heat leaks, inward or outward.

i. Spaces of uniform thickness are bounded by moderately smooth surfaces.

j. Values shown are not applicable to interior installations of materials listed.

k. Winter is heat flow up; summer is heat flow down, based on area of opening, not on total surface area. Derived from data from ASHRAE Handbook of Fundamentals (1977), Chapter 22.

Contributor:

John I. Yellott, PE, College of Architecture, Arizona State University, Tempe, Arizona.

WINDOW FRAME TYPES

WINDOW FRAME DETAILS

2.400

Contributors:

John Carmody, University of Minnesota, Minneapolis, Minnesota; Stephen Selkowitz, Lawrence Berkeley National Laboratory, Berkeley, California.

WINDOW FRAME TYPES

2.401

WINDOW INSTALLATION

Regardless of the quality of the window unit, ultimate performance depends on proper installation. The intersection of the window frame with surrounding walls has always been a difficult detail, and light modern materials have exacerbated the problem. AAMA 2400, “Standard Practice for Installation of Windows with a Mounting Flange in Stud Frame Construction,” and ASTM E 2112-01, “Standard Practice for Installation of Exterior Windows, Doors and Skylights,” both establish a variety of methods for quality installations.

The architect may desire to exceed the standard installation practices for more durable and dependable service. In particular, it is recommended that you always provide a subsill of sheet metal or other impervious material, with watertight end dams and a slope to the exterior, and avoid penetrations in the horizontal portion of the sill.

Qualified installers who understand the importance of many detailed tasks to the overall level of quality are essential. Consider AAMA Certified “Installation Masters” or similar independently trained and certified installers.

For more information, see the AAMA Window Selection Guide.

WOOD WINDOW WEATHERPROOFING DETAILS

2.402

NOTES

2.402 a. Caulking, sealant, adhesive, or gasket seals window framing and wall joints to form air barrier.

b. These principles are also applicable to door weatherproofing.

Contributors:

John Carmody, University of Minnesota, Minneapolis, Minnesota; Stephen Selkowitz, Lawrence Berkeley National Laboratory, Berkeley, California.

SEALING MOUNTING FLANGES

2.403

FRAME CORNERS

2.404

FLANGED RESIDENTIAL WINDOW WEATHERPROOFING

2.405

RESIDENTIAL WOOD WINDOW HEAD DETAIL

2.406

RESIDENTIAL WOOD WINDOW JAMB DETAIL

2.407

RESIDENTIAL WOOD WINDOW SILL DETAIL

2.408

NOTES

2.403 Follow manufacturer’s instructions.

2.404 Inspect frames, and add sealant to increase resistance to water penetration.

2.405 a. Install weather barrier above head (not shown, for clarity).

b. Install expanding foam seal between rough opening and window frame on four sides (not shown).

Contributors:

John F. Kaulbach, AIA, Kling, Philadelphia, Pennsylvania.

TYPICAL HEAD AT CAVITY WALL

2.409

TYPICAL WINDOW JAMB AT CAVITY WALL

2.410

TYPICAL SILL AT CAVITY WALL

2.411

ALUMINUM HEAD DETAIL

2.412

Contributor:

Bernard E. Suber, Kling, Washington, DC.

ALUMINUM SILL DETAIL

2.413

TYPICAL STOREFRONT

2.414

STOREFRONT DESIGN AND DETAILS

Glass and metal frame storefront systems typically are designed to allow good views into and out of ground-level commercial spaces. Metal members and glass sections are assembled on-site to form both wall and entrance systems, which typically are attached to the floor structure below and the bottom of structure above, or to a suspended structural frame above the ceiling. Storefront systems typically have lower resistance to air and water infiltration, and less structural performance. Most storefront systems are not pressure-equalized, but do manage water that penetrates into the glazing pocket. Watertight subsills with end dams are required.

Storefront systems design involves these considerations:

• Storefront systems are available in a variety of attachment/ assembly types, depending on the structural or aesthetic design and on the manufacturer. Glass and metal materials come in various shapes, colors, profiles, and structural capabilities.

• Applicable codes must be consulted for safety requirements, glass size, thickness, and tempering. Consult all applicable codes, standards, and regulations for accessibility requirements. These may include requirements for hardware, thresholds, opening forces, and closing speeds.

• Manufacturers’ data on structural adequacy must be consulted for required loads, and for frame and transom bar reinforcement. Calculations for deflection and wind-load stresses must be considered in the design of storefront systems. Reinforcing for required loads can be provided by steel reinforcing inserts or by use of a heavier metal mullion profile. Consult a structural engineer for analysis and design.

• The height of entrance doors is typically 7 ft 0 in. Typical door widths are 3 ft 0 in., 3 ft 6 in., pair of 2 ft 6 in., pair of 3 ft 0 in. For accessible doors, at least one leaf of a pair must be 32 in. minimum clear width.

• Perimeters of storefront systems are difficult to detail for both an outer seal and an inner air/vapor barrier seat. Therefore, limit use to low-rise construction, preferably under canopies or overhangs in areas of heavy rainfall.

• Select systems with thermal break and condensation resistance factor (CRF) to suit interior and exterior conditions.

SNAP-TOGETHER/SCREW SPLINE STOREFRONT ASSEMBLY

2.415

NOTE

2.415 The head, intermediate horizontal profile, and sill members are screwed to vertical members at predrilled locations.

Contributor:

Daniel F. C. Hayes, AIA, Washington, DC.

SHEAR BLOCK STOREFRONT ASSEMBLY

2.416

WALL SECTION AT STOREFRONT

2.417

BYPASS DOOR DETAILS

2.418

POCKET DOOR DETAILS

2.419

SLIDING STOREFRONTS AND MULTIPLE SLIDING DOORS

When working with sliding storefronts and multiple sliding doors, these considerations apply:

• Sliding glass door wood finishes are available in clear pine with natural varnish, primed, or painted finishes.

• Cladding for wood doors is available in vinyl or aluminum with electrostatic paint or in anodized aluminum.

• Aluminum frames are available anodized or with electrostatic paint finishes.

• Check with manufacturer’s literature for material, cladding, and color options.

• For pocket doors required to be accessible, refer to all applicable codes, standards, and regulations for specific requirements.

• Refer to all applicable codes, standards, and regulations for specific requirements for doors that must be accessible.

Contributor:

Daniel F. C. Hayes, AIA, Washington, DC; Joseph A. Wilkes, FAIA, Wilkes and Faulkner, Annapolis, Maryland.

MULTIPLE SLIDING DOOR DETAILS

2.420

ALL-GLASS STOREFRONT

2.421

STOREFRONT SYSTEMS

Keep the following in mind when working with storefront systems:

• Storefront systems typically require a watertight sill or subsill to direct water within the system to the exterior, unless interior or protected by a large overhang. Verify the manufacturer’s details and customize the system to suit the project.

• Review tinted- and coated-glass applications and details to eliminate the possibility of thermal breakage caused by shading devices and shadow patterns.

• Review setting-block spacing, size, and hardness to prevent glass slippage and breakage.

• Weep holes are required at sill for double glazing.

• Other materials such as hollow metal or wood can be used for custom work and in saltwater atmospheres where aluminum will corrode.

• Various aluminum anodized color finishes are available. Class I (0.7 mil) and Class II (0.4 mil) in black, bronze, or clear, are standard with most manufacturers. Class I is recommended for most exterior applications.

• To extend life of aluminum and to reduce the tendency of surface pitting, wash aluminum periodically with water and mild detergent.

• Glass edges mitered at corners are not recommended. Maximum vertical span for butt glazing is 10 ft by 8 ft wide.

• Mullions are clear glass. Tinted or coated glass lights may be considered for small areas. Maximum vertical span is 30 ft.

• Care should be taken to protect the public from the possibility of overhead glass breakage. Laminated glass provides the highest level of protection, but fully tempered glass may be acceptable.

• Higher bulkheads can be built up with aluminum tubing and applied stops. Locate expansion mullions 20 ft o.c.

• Use receptor for deflection or dimensional tolerance.

Refer to manufacturer’s current recommendations for specific applications.

CENTER GLAZED

2.422

OFF-CENTER GLAZED

2.423

FACE GLAZED

2.424

APPLIED STOPS

2.425

Contributor:

Joseph A. Wilkes, FAIA, Annapolis, Maryland; Eric K. Beach, Rippeteau Architects, PC, Washington, DC.

BUTT-GLAZED WITH FLUSH HEAD AND JAMB

2.426

GLASS MULLION

2.427

THERMAL GLAZING

2.428

SLOPED GLAZING

2.429

ANGLED CORNER

2.430

BULKHEAD SILL

2.431

EXPANSION MULLION

2.432

DOOR TRANSOM WITH CLOSER AND ILLUMINATED EXIT SIGN

2.433

HEAD WITH RECEPTOR

2.434

GLAZED CURTAIN WALL

The term curtain wall was used in the early days of modern architecture to describe virtually any enclosure system that was supported by the building frame, as opposed to masonry or other bearing walls. A modern curtain wall is most typically thought of as a metal frame, usually aluminum, with large areas of glass. Other materials of metal or stone can be used to infill the frame at opaque areas (such as spandrels at floor framing). The frames span past, and are supported by, the floor edges, as opposed to bearing on the floors or spandrel beams. Gravity loads are frequently supported at every other floor, with lateral supports for lateral load only at floors between.

CHARACTERISTICS

A curtain wall is typically manufactured using one of the following methods:

• Standard commercial systems use collections of typical mullion sections and accessories, which are selected, fabricated, reinforced, and assembled into custom-sized walls to suit the project.

• Custom systems are designed specifically for the project, using specially designed mullions, parts, and accessories. The cost of custom design and engineering is offset by the efficiency of scale inherent with large projects.

Curtain wall water-penetration management methods:

• The highest-performing systems are fully pressure-equalized rainscreen systems, with the glazing pocket around each individual light a pressure-equalization chamber that is separated from other lights, weeped, and vented.

• Nonpressurized systems tend to direct water that penetrates the outer seals to vertical mullions, and then weeps at the base of wall.

Curtain wall installation methods:

• Stick systems assemble individual vertical and horizontal mullions on-site, and infill with glass, metal, stone, or other panels. Stick systems require careful attention to sealing the intersecting members.

• Unitized systems are substantially factory assembled off-site, complete with frames, glazing, and as much trim or accessories as reasonable. The panels are typically between 5 and 10 ft wide, and one or two stories high. The unitized panels are hoisted onto the wall and anchored in place. Unitized panels are more often a custom system than stick systems, and are used more often on large or high-rise projects. Because the sealing of the intersecting members takes place in a shop or factory, they are more likely to be well made. However, the connections between units are blind and, therefore, must be carefully engineered and verified by mockup testing.

Curtain wall glazing types:

• Pressure plate glazing: In this system, the glass and infill panels are installed from the exterior of the building. Pressure plate glazing allows for sealing of all joints in the framing and easy integration with an air/vapor barrier. Toe beads, cap beads, or complete wet glazing are possible to improve performance. However, all of the glass must be handled from scaffolding or lifts.

• Dry glazing: In this system, the glass and infill panels are installed from the interior. The exterior frame is fixed and glazing gaskets are installed. Typically, only the top mullion has a removable interior stop. The glass unit is slid into a deep glazing pocket on one jamb far enough to allow clearing the opposite jamb, then slid back and dropped into the sill glazing pocket. The removable interior stop is applied and, finally, an interior wedge gasket is installed. Sometimes this method is called “jiggle” or “wiggle” glazing because of the manipulation necessary to get the glass into place. Installation of the glass units from inside the building is desirable from a constructability standpoint, but performance is slightly reduced because dry metal-to-metal joints result at the removable stop at a point that should be airtight and watertight. Heel beads will improve performance, and some systems incorporate an extra gasket to form an air seal between frame and glass. Installation of spandrel areas may have to be done from the exterior because of limited access space on the interior side.

• Structural silicone glazing (SSG): This system depends on adhering the glass to the frame or other glazing with a bead of silicone. Outer silicone weather seals supplement the structural seal. Unitized systems are frequently structural silicone-glazed because this allows work from one side only, and is highly reliable. Two-sided SSG can be completed in the field with either pressure plate or jiggle-glazed frames in the other direction. Four-sided SSG should only be done under controlled conditions in a factory. If the frames are stick-built, then an aluminum subframe is adhered to the glass at the factory, and the resulting assembly is mechanically fastened to the main frame in the field.

Water management for nearly all curtain walls utilizes pressure-equalized rainscreen technology.

PERFORMANCE

Standardized levels of performance for curtain walls are not commonly available in the industry, but standardized test procedures and ranges of typical values are relatively well known.

• Structural capacity of a curtain wall is tested according to ASTM E 330, “Standard Test Method for Structural Performance of Exterior Windows, Curtain Walls, and Doors by Uniform Static Air Pressure Difference.” The loads required for the project are determined by code, normally ASCE-7. For large projects, boundary-condition wind-tunnel testing may be performed to establish more accurate wind loads. Wind-tunnel testing may lower the average field loads and may also help identify hot spots of higher loads.

• Air infiltration is tested according to ASTM E 283, “Standard Test Method for Rate of Air Leakage Through Exterior Windows, Curtain Walls, and Doors,” with values of leakage tested at certain differential pressures. Common leakage values are 0.06 cfm per sq ft of wall area. Common test pressures are 1.56 psf (25 mph wind) for low-rise, 6.24 psf (50 mph) or 10 psf (63 mph) for midrise construction, and 12 psf (70 mph) and up for high-rise or monumental buildings. Pressures are also selected at approximately 20 percent of the structural loads.

• Water leakage is tested according to ASTM E 331, “Standard Test Method for Water Penetration of Exterior Windows, Curtain Walls, and Doors by Uniform Static Air Pressure Difference,” and AAMA 501.1, “Standard Test Method for Metal Curtain Walls for Water Penetration Using Dynamic Pressure.” Test pressures usually match those for air infiltration. The architect should establish leakage criteria—frequently acceptable are water amounts appearing on interior sills small enough to not run off the mullion. The static pressure test is more common, but might give an optimistic result because the test procedure may suck glass against gaskets, making a better than expected seal. Dynamic testing, which may help reveal leaks that would occur under the buffeting conditions of variable winds, is particularly effective at operable sash.

• Thermal performance is tested according to AAMA 501.5, “Test Method for Thermal Cycling of Exterior Walls.” U-values should be specified by the design team. Condensation performance is extrapolated from the thermal performance.

Standardized test procedures also are available to evaluate numerous specialized performance criteria, including acoustic isolation, blast resistance, forced-entry resistance, hardware, and safety impact. Refer to AAMA. Standardized tests such as cyclical structural loading, frame racking, and thermal cycling are available to rapidly simulate aging of the sample. The tests for air and water infiltration are repeated after the accelerated aging to determine the likely long-term performance of the wall.

Manufacturers’ standard systems are tested for performance in a range of sizes. The design professional must determine the applicability of the tests to specific project conditions. Custom testing may be necessary to accurately predict acceptable performance. Custom systems or unusual configurations of standard systems require testing of job-specific mockups. Testing protocols for custom markups are specified by the design professional and should include confirmation of all criteria.

DETAILING

Manufacturers of curtain walls typically provide generic details for installation. Adjacent construction is frequently shown as a hatched single line. Detail the curtain wall frame in project-specific assemblies.

• Mullions and covers: Standard rectangular commercial mullions are available from manufacturers in widths from 2 to 3 in. (2-1/2 in. is most common), in depths from 1 to 12 in. from the inside face of glass. Snap-on mullion covers are available in many shapes, and can be easily customized because they have limited impact on the performance of the curtain wall. Large external mullion covers, however, may seriously affect the thermal performance of systems without complete thermal breaks.

• Interface with adjacent assemblies: Seal the air barrier of the curtain wall to the wall air barrier; likewise the rainscreen. Utilize subsill flashing at the base of the wall, detailed to seal to the air barrier. At the interface with barrier walls, provide a dual line of sealant.

• Air barriers: Detail the curtain wall installation so that the line of air barrier (if required) extends uninterrupted across the gap at the perimeter of the curtain wall by connecting to the inner shoulder of the glazing pocket.

• Anchoring: Curtain walls are typically anchored to each floor slab or spandrel beam. Every other floor is a gravity and wind anchor, with a wind-only slip anchor in between. The anchorage scheme should be determined by the architect and structural engineer, and indicated on the drawings. Unitized panels commonly have a wind and gravity anchor at each floor, with slip joints providing wind load resistance at the stack joints. Anchors for stick systems are commonly mounted on the side of beams or slab edge. Anchors for unitized panels are commonly mounted in pockets on the top of slabs. Manufacturers have a variety of proprietary anchors that allow three-dimensional adjustment and fixed or slip connection.

• Movement: Because curtain wall spans floor-to-floor from slab or spandrel beam, it must accommodate differential movement of the spandrel beams and lateral drift of the structure along with the large thermal movement inherent with aluminum. Curtain wall heads (particularly at strip curtain wall) often are located at shelf angles and must accommodate movement typically in the range of 1/2 in. from above.

• Thermal continuity: Detail the curtain wall to maintain a line of thermal insulation in the same plane as in the tested configuration, and as intended by the curtain wall manufacturer.

• Firestopping: The intersection of a floor slab with curtain wall requires firestopping.

• Spandrel/shadowboxes: Where curtain wall is in front of a structure or areas that otherwise need to be opaque, spandrel glass or a shadowbox is used. Spandrel glass is composed of single or insulated glass units, with the inside layer opacified by a film or fired-on ceramic frit. Reflective coating can be used. If an insulated glass unit is used, the second or third surface can be coated with patterned ceramic frit. Shadowboxes are more effective at blending spandrel areas with vision areas, especially if the back panel is reflective. As opposed to spandrel areas, the cavity inside the shadowbox is typically vented and weeped, but there are differences of opinion among experts and manufacturers regarding venting of the cavity. Vented airspaces shift the thermal enclosure to the back of the curtain wall and may result in thermal short circuits and uncontrolled condensation; and, in time, the inside surface may get dirty. Unvented shadowboxes may overheat, especially with clear glass. Note that heat buildup within shadowbox cavity can cause offgassing of sealants and plastics of some materials and may deform composite materials and insulation. The manufacturer can assist with analysis.

• Parapets and copings: When curtain wall extends past the edge of the roof, the curtain wall becomes a parapet. Special care must be taken to stop air movement through hollow mullions and to control the thermal conduction to the exterior. Most curtain wall systems are not designed for exposure to weather from the back side, but they can be modified to properly function. If a spandrel of shadowbox is used for an opaque parapet, the back of the curtain wall can be furred, sheathed, and waterproofed with roofing base flashing. Transparent or translucent parapets can be provided by terminating the roof base flashing at a mullion approximately 8 in. above the roof. Special precautions must be taken because the back surface of curtain wall is typically not watertight. Curtain walls extending past the conditioned space into the parapet can create thermal short circuits and uncontrolled condensation. Provide air seals to prevent moisture-laden air from contacting cold surfaces, both inside the mullions and between the mullions and the roof structure. Foam-in-place sealants work well. Because of the inherent thermal break with extending a curtain wall to form a parapet, it is best avoided in cold climates. Thermal analyses can check insulation and air/vapor barriers design to verify that temperatures never reach dew points. Extend roof base flashing or membrane flashing across the top of the parapet and seal into the glazing pocket. Cap with brake metal coping, which is also sealed into the glazing pocket.

INSTALLATION

Whatever the quality of the curtain wall, ultimate performance depends on proper installation. The intersection of the curtain wall frame with surrounding walls has always been a difficult detail, and light modern materials have exacerbated the problem.

Stick systems require a high level of quality control in the field, as there are numerous extremely important and detailed steps in the assembly of the curtain wall.

• Anchors and mullions must be installed to allow movement.

• Joints at the mullion intersection must be made airtight and be properly compartmentalized for pressure-equalized systems.

• Glazing gaskets must be cut precisely and the corners sealed.

• Pressure plates must be torqued to specified values to compress the gaskets sufficiently for watertight performance.

Even unitized systems require attention to detail during field installation but because more assembly takes place in the factory there are fewer crucial requirements. The most important point is the flashing of the four-way intersection.

STICK AND UNITIZED CURTAIN WALL CONSTRUCTION

2.435

ATTACHMENT AND ANCHORAGE DETAILS

2.436

TYPICAL PRESSURE-PLATE MULLION

2.437

NOTES

2.436 a. Anchorage devices must permit three-dimensional adjustment. Metal-to-metal connections subject to unintentional movement should be designed to eliminate noise caused by movement due to temperature change.

b. Anchors must be designed to withstand wind loads acting outward and inward.

c. Anchors must be permanently secured in position after final assembly and adjustment of wall components.

d. All anchorage members must be corrosion-resistant or otherwise be protected against corrosive forces.

e. Shim plates may be installed between vertical angle anchor and concrete structure, as required.

TYPICAL DRY-GLAZED MULLION

2.438

MULLION SNAP-ON COVER OPTIONS

2.439

TWO-SIDED STRUCTURAL GLAZING SYSTEM WITH STRUCTURAL SILICONE JOINT SEALANT

2.440

GRID SYSTEM (STICK OR STUD), ALUMINUM PRESSURE BAR

2.441

TYPICAL FOUR-SIDED STRUCTURAL SILICONE GLAZING, CUSTOM-UNITIZED SYSTEM

2.442

MULLION DETAIL 1 AT SPANDREL GLASS—VERTICAL PANEL JOINT

2.443

MULLION DETAIL 2 AT VISION GLASS—VERTICAL PANEL JOINT

2.444

MULLION DETAIL 3 AT OUTSIDE CORNER—VERTICAL PANEL JOINT

2.445

NOTE

2.441 Horizontals are weeped for positive performance against water infiltration, with slots at glazing pressure plate and holes at cover.

MULLION DETAIL 4 AT INSIDE CORNER—VERTICAL PANEL JOINT

2.446

COPING DETAIL 5

2.447

HEAD DETAIL 6

2.448

SILL DETAIL 7, AT HORIZONTAL

2.449

FLOOR SLAB DETAIL 8

2.450

GRADE DETAIL 9

2.451

SHADOWBOX AND SPANDREL ASSEMBLIES

2.452

SILL AT GLAZED PARAPETS

2.453

CURTAIN WALL PARAPET

2.454

SPECIALIZED CURTAIN WALL

Design professionals have been challenging the traditional assumptions regarding the support and glazing of curtain walls. These walls have frequently been utilized in large lobbies, atria, and other monumental-scale spaces, but they have also been used to enclose entire buildings. More sophisticated, lightweight, and visually transparent wall support structures have been developed, including architectural exposed structural steel trusses, trusses with cable and rod tension members, tension grid supports, glass mullions and support fins, the use of the glass itself as part of the load-resisting components, and other innovative solutions. The glazing of these systems frequently depends on point support devices or patch fittings at corners, and silicone butt glazing, resulting in a frameless, visually uninterrupted surface.

Specialized curtain walls require extremely close coordination between the architect, structural engineer, manufacturer, installer, and other contractors. In particular, if the glass is used structurally, there are relatively few engineers qualified to perform the analysis and few installers who understand the difficult sequencing required to temporarily hold the wall in place until all components can be tensioned to design values. The following are issues:

• Heat gain/loss and glare control can become sizable problems with large areas of glass. Shading and specialized glass are required.

• The adjacent building structure may need to accommodate large loads resulting from suspending walls that might otherwise be gravity-loaded to a foundation or to resist large tension loads.

• The interface with surrounding walls, copings, and roofs may need to accommodate significant movement within and between the systems.

NOTES

2.452 a. A spandrel and shadowbox typically occurs at anchorage points. Coordinate size and location of anchors with insulation and panels, and seal penetrations.

b. Shadowbox 2 provides the best thermal isolation of the cavity.

STRUCTURAL STEEL SUPPORT—LONG-SPAN CURTAIN WALL

2.455

TENSION CABLE TRUSSES—LONG-SPAN CURTAIN WALL

2.456

TENSIONED CABLES—LONG-SPAN CURTAIN WALL

2.457

GLASS SUPPORTS—LONG-SPAN CURTAIN WALL

2.458

NOTES

2.455 a. Weather and thermal barriers must continue above curtain wall. They are not shown, for clarity.

b. Some or all of the steel components may be solid or laminated timber.

c. Structure above must accommodate large horizontal loads from vertical members.

2.456 Weather and thermal barriers must continue above curtain wall. They are not shown, for clarity.

2.457 Weather and thermal barriers must continue above curtain wall. They are not shown, for clarity.

2.458 Weather and thermal barriers must continue above curtain wall. They are not shown, for clarity.

POINT SUPPORT

2.459

DOUBLE FAÇADE CURTAIN WALL

A double façade curtain wall, as the name suggests, utilizes two layers of a separate wall system with a cavity between. The cavity creates a mediating environment between the interior and exterior, resulting in warmer interior glass surface temperatures, for improved occupant comfort and better acoustic performance. The cavity can also be used to provide natural or mechanically induced ventilation, especially on high-rise buildings where natural ventilation might otherwise be impossible. Shading devices can be installed in the cavity. Cavity size varies, with two primary approaches. The first approach is with small cavities of approximately 6 in. with one of the wall layers having an operable sash to access the cavity. The second approach is with cavities wide enough, generally around 3 ft, for maintenance access.

The value of double façade curtain walls outside of Europe has not been clearly proven, as they are very expensive and payback periods for energy savings may be long. There are other, more cost-effective ways to gain most of the performance enhancements offered by double façades—double façades as retrofits of existing curtain wall may be a good choice. Older curtain wall is frequently single glazed, and the gaskets may be dried. However, removal of the existing curtain wall may cause unacceptable disruptions to existing activities. Adding a new layer of wall outside the existing may be a cost-effective and minimally invasive solution.

DOUBLE FAÇADE CURTAIN WALL 1

2.460

DOUBLE FAÇADE CURTAIN WALL 2

2.461

CHANNEL GLASS CURTAIN WALL

2.462

CHANNEL GLASS CURTAIN WALL

Channel glass walls are composed of single or double layers of extruded glass channels, silicone-sealed together and held at head and sill in an extruded track. The walls are translucent rather than transparent. The double-layer walls are thermally efficient if frames are also thermally broken.

Consult the following references:

• Double-Skin Façades by Eberhard Oesterle, Rolf-dieter Lieb, Martin Lutz, and Winfried Heusler (Munich, Germany: Prestel Verlag, 2001)

• Glass in Architecture by Michael Wigginton (New York City, NY: Phaidon Press Ltd, 1996)

EXTERIOR DOORS

DESIGN CONSIDERATIONS

Exterior doors allow access and egress, while maintaining a separation between the interior and exterior environments. Doors must also provide security from intrusion, and may need to be fire rated.

Doors and frame types include:

• Hollow metal doors and frames: These comply with performance standards in the Hollow Metal Manual, by the Hollow Metal Manufacturers Association (HMMA) and NAAMM and the Steel Door Institute (SDI).

• Residential prehung doors: These include insulated. metal-skinned, fiberglass-skinned, and wood doors in wood or metal frames. Refer to AAMA/WDMA/CSA 101/I.S.2/A440, “Standard/Specification for Windows, Doors, and Unit Skylights.” Drafts and heat loss from residential doors present a larger problem than for commercial buildings. It is likely that the comfort of the occupants will be affected to a greater degree, and that the energy loss will result in a greater impact on the overall energy usage.

• Aluminum and glass entrance doors: This type includes door frames of extruded aluminum with glass or insulated aluminum infill panels. Standardized test procedures are available to evaluate many specialized performance criteria, including acoustic isolation, blast-resistance, forced-entry-resistance, and safety impact. Refer to AAMA.

• Specialty entrance doors: Tempered safety-glass doors, frameless with patch fittings, with top and bottom rails or with solid metal frames, are available on a custom basis for monumental entrances. Refer to GANA.

ACCESSIBILITY

Entrance doors are not limited by IBC or ADAAG for operating force for accessibility, primarily because the low force is not sufficient to keep the doors closed against wind pressures. However, this should be verified, as some local codes do have maximum operating forces.

It is good practice to provide automatic doors at entrances to public buildings to allow for universal access. Overhead concealed and exposed operators, as well as operators concealed in the floor, are available. Push button, card key, or motion sensor activators can be used.

Thresholds must provide a continuous walkable surface, with minimal vertical offsets to allow for universal access that is free from tripping hazards and impediments to wheeled traffic. The lack of vertical offset can create an opportunity for water to be pushed under doors by wind pressure, so compensate with generous canopies or overhangs and ensure that the paving slopes away. Trench drains with closely spaced grilles immediately in front of doors will also stop water.

INSTALLATION

Regardless of the quality of the door and frame, ultimate performance depends on proper installation. The intersection of the doorframe with surrounding walls has always been a difficult detail, and light modern materials have exacerbated the problem.

ASTM E 2112, “Standard Practice for Installation of Exterior Windows, Doors, and Skylights,” establishes a variety of methods for quality installations of prehung residential doors. The architect may exceed the standard installation practices for more durable and dependable service. In particular, it is recommended that you coordinate waterproofing, dampproofing, and flashing below grade with the threshold.

Door installation must be detailed as appropriate for the generic wall assembly types, which include:

• Barrier walls: Seal the door frame to the barrier. Use a subsill flashing to avoid introducing water into the wall. For massive barrier walls such as precast concrete, head flashing may be required to ensure that water seepage does not get behind the window.

• Drainage plane walls: Provide the primary seal of the doorframe to the water-resistant drainage plane, and an outer seal in line with the wallcovering. The flashing below the threshold should extend past the doorframes and be lapped by the water-resistant drainage plane in the wall. Ensure continuity of the air barrier, wherever it is located in the wall assembly.

• Drainage cavity walls: Provide the primary seal of the doorframe to the waterproof inner line of protection, and an outer seal to the outer wallcovering. The flashing below the threshold should extend past the doorframes and be lapped by the water-resistant barrier in the wall. Ensure continuity of the air barrier if it is not located at the inner line of protection.

• Pressure-equalized (PE) rainscreen walls: Use doorframes that incorporate PE rainscreen technology. Seal the air barrier of the door frame to the wall air barrier; likewise for the rainscreen. The flashing below the threshold should extend past the doorframes and be lapped by the air/vapor barrier in the wall.

• Air and vapor barriers: Detail the door installation so that the line of the air barrier and/or vapor barrier (if required) extends uninterrupted across the gap at the perimeter of the doorframes.

These organizations can be contacted for more information:

• Hollow Metal Manufacturers Association (HMMA)

• Steel Door Institute (SDI)

• American Architectural Manufacturers Association (AAMA)

• Window and Door Manufacturers Association (WDMA)

GLASS ENTRANCE DOORS

Keep the following in mind when working with glass entrance doors:

• Consult applicable codes for safety requirements, glass size, thickness, and tempering.

• Frameless 1/2-in. glass doors are available in clear, gray, or bronze tints, in sizes up to 60 by 108 in. Frameless 3/4-in. glass doors are available only in clear tint in sizes up to 48 by 108 in.

• Consult manufacturers’ data on structural adequacy for required loads and for frames and transom bars reinforcement.

• Aluminum doors and frames are available in all standard aluminum finishes in sizes up to 6 by 7 ft.

• Frameless doors may not permit adequate weather stripping. The use of frameless doors in exterior walls in northern climates should be evaluated for energy efficiency and comfort.

• Refer to all applicable codes, standards, and regulations for specific requirements for doors that must be accessible.

HOLLOW METAL JAMB DETAIL

2.463

ALUMINUM ENTRANCE JAMB DETAIL

2.464

GLASS DOOR TYPES

2.465

NOTE

2.465 Doors with narrow stiles should not be used in heavily trafficked areas.

ELEVATION—TYPICAL GLASS ENTRANCE DOORS

2.466

DETAILS—TYPICAL GLASS DOORS

2.467

BALANCED DOOR

2.468

REVOLVING DOORS ENTRANCES

The are points to consider when working with revolving doors:

• Circular glass enclosure walls may be annealed 1/4-in. glass. However, this varies with different government bodies. Some jurisdictions require laminated glass. Tempered glass is not available for this use. Refer to the Consumer Products Safety Commission’s standards for glazing.

• Practical capacity equals 25 to 35 people per minute.

• Doors fabricated from stainless steel, aluminum, or bronze sections are available. Stainless steel is the most durable; lead times vary with construction techniques. Stainless steel is available in a number of satin and polished finishes. Aluminum is the most common and economical. It is available in anodized or painted finishes. Bronze is most difficult to maintain; satin, polished, or statuary finishes must have a protective lacquer coating. Doors are available, with only top and bottom stiles to be used with all-glass storefront doors. Wall enclosures may be all metal, all glass, partial glass, or housed-in construction.

• Optional heating and cooling source should be placed immediately adjacent to the enclosure.

• For general planning, use 6-ft 6-in. diameter. For hotels, department stores, airports, or other large traffic areas, use a 7-ft or greater diameter.

• Codes may allow 50 percent of legal exiting requirements by means of revolving doors. Some do not credit any, and require hinged doors adjacent. Verify with local authorities.

TYPES AND APPLICATIONS

Revolving door types and applications include:

• Automated revolving doors for large-size doors

• Motorized oval doors for small groups or grocery carts

• Security revolving doors that are noncollapsible until a magnetic shear lock is automatically released in an emergency

• Sliding night door of solid metal construction to close off open quadrant at exterior opening

• Manually operated

DESIGN CONSIDERATIONS

Revolving door design guidelines include the following:

• Mount entirely on one slab.

• Do not attach to adjacent walls.

• Floor must be level.

Swing doors may be required in addition to revolving doors by code or for good practice to provide egress, to meet accessibility requirements, or for off-hours security operation.

TYPICAL REVOLVING DOOR

2.469

REVOLVING DOOR ENCLOSURE DIMENSIONS

2.470

LAYOUT TYPES

2.471

NOTE

2.471 A swinging door may be provided as well, for egress accessibility.

Contributor:

Jane Hansen, AIA, DeStefano & Partners, Chicago, Illinois.

SPECIAL DOORS

COILING OVERHEAD DOOR SECTION

2.472

SECTIONAL DOORS

UPWARD-ACTING SECTIONAL DOORS

2.473

INSTALLATION DETAILS

2.474

WOOD SECTIONAL DOORS

2.475

SECTIONAL DOOR DETAILS

2.476

NOTES

2.472 a. Standard commercial doors are designed to wind loads of 20 lb/sq ft.

b. Glazing may be safety glass, plexiglas, or wired glass.

c. Motor operators may be turned on and off by remote electrical switch, radio signal, photoelectrical control, or key lock switch, for security.

2.473 Consult manufacturers for other door track configurations and clearances.

2.475 a. Typical maximum width for wood panel sectional doors is 24 ft (6 panels); typical maximum height is 18 ft (9 sections).

b. Typical maximum width for flush wood sectional doors is 24 ft (6 panels); typical maximum height is 18 ft (9 sections).

Contributors:

Richard J. Vitullo, AIA, Oak Leaf Studio, Crownsville, Maryland; Daniel F.

C. Hayes, AIA, Washington, DC.

METAL SECTIONAL DOORS

2.477

STANDARD HEADROOM—2″ OR 3″ TRACK

2.478

FULL VERTICAL TRACK

2.479

LIFT CLEARANCE TRACK—2 OR 3 IN.

2.480

LOW-HEADROOM TRACK—2 IN.

2.481

NOTES

2.477 a. Typical maximum width for aluminum sectional doors is 18 ft (5 panels); typical maximum height is 14 ft (7 sections).

b. Typical maximum width for steel sectional doors is 24 ft (7 panels); typical maximum height is 18 ft (9 sections).

c. Typical maximum width for metal and fiberglass sectional doors is 20 ft (6 panels); typical maximum height is 16 ft (8 sections).

2.478 Available with torsion or extension spring counterbalance. Vertical tracks can be bracket- or angle-mounted.

2.479 Torsion spring or weight counterbalance. Tracks can be bracketor angle-mounted.

2.480 Torsion spring counterbalance only. Tracks can be bracket- or angle-mounted. Maximum usable headroom is 11 ft 6 in.

2.481 a. Available with torsion or extension spring counterbalance. Vertical tracks can be bracket or angle mounted.

b. Low-headroom track used on doors to 18C sq ft., 500 lbs, or 13 ft 1 in. high.

c. Headroom up to 144 sq ft. is 6 in.

d. Headroom from 144 sq. ft. to 180 sq ft. is 10 in.

Contributor:

Daniel F.C. Hayes, AIA, Washington, DC.

ROOFING

DESIGN CONSIDERATIONS

Roofing generally falls into two broad categories, steep slope and low slope. Selecting the appropriate roof assembly is dependent on many factors, including:

• Initial and life-cycle cost

• Reliability

• Substrate material

• Structural capacity of the deck

• Fire-resistance

• Environmental conditions including wind speed, seasonal weather (hail, snow, and rain)

• Building height

• Future access

• Roof mounted equipment

• Complexity of the building geometry

• Number of penetrations

• Thermal performance

• Construction sequencing

• Building codes

STEEP SLOPE ROOFING

Steep slope roofing is generally designated as roofing with slopes greater than 3 in 12. Steep slope roofing is a water-shedding roof, typically composed of many small overlapping units; as such, it is not a continuous waterproof membrane. The slope must be steep enough so that water runs off by gravity and cannot be pushed uphill by wind or capillary action. Some steep slope roof assemblies can be installed at slopes less than 3 in 12 in accordance with the manufacturer’s recommendations.

CHARACTERISTICS AND CONSIDERATIONS

Steep slope roofing is typically a ventilated or “cold” roof design, with insulation below the roof deck and the surface temperature of the roofing system near outdoor conditions. The insulation and weather barrier are typically located at the ceiling below the attic cavity.

Steep slope roofing assemblies can be designed as a compact “warm” or “unvented” roof design with insulation between the shingles or covering and the structural deck. Evaluate the manufacturer’s recommendations for compact roof design, because there may be concerns about the possibility of elevated surface temperatures causing premature failure of the assembly. Forensic investigation has shown that roof orientation (south versus north slopes) and material color have a major impact on surface temperature.

Steep slope roofing is most commonly used for residential and light commercial construction. Although it provides long-term performance at competitive costs, it is generally cost-effective for use on large commercial buildings because it does not provide a platform for roof-mounted HVAC or window cleaning equipment, nor is it as easy to maintain or replace on tall buildings. For buildings with large footprints, steep slope roofing can result in excessive internal volume that is not usable.

Roof warranties are offered by most manufacturers of synthetic roof shingle materials, but not for natural products such as slate and wood. However, these warranties are primarily a means for manufacturers to limit their liability, rather than to protect an owner. Furthermore, some products are promoted as having extremely long warranty periods, but the fine print limits coverage to replacement of defective materials on a prorated cost basis to the original owner. Defective installation is not covered, nor is there any value available for the cost of labor to make repairs. Therefore, design professionals should read the warranty carefully, and not rely on it as a basis for product selection. In the end, keep in mind that no piece of paper will keep water out of a building, and a warranty only provides a road map to fixing a leak after it has occurred.

Selecting the steep slope roof system is dependent on many factors, including initial and life-cycle costs, appearance, reliability, historical accuracy, structural capacity of the deck, fire-resistance, wind speed, resistance to weather conditions including hail, rain, and snow, building codes.

Selection recommendations include:

• Consider light-colored, highly reflective roofs to reduce heat island effect in cities and, in warm climates, energy costs for the building.

• In areas susceptible to forest fires, select noncombustible roofing such as concrete or clay tiles, or slate.

• Consider recycled material content, life span, reuse, embodied energy, distance to source, and other sustainable criteria.

Steep slope roofing consists of four major components: the roof covering; the weather barrier; the structural roof deck; and flashing at the edges, transitions, and penetrations.

WEATHER BARRIER

Steep slope roofing is almost always installed over a weather barrier that provides temporary protection until the roofing is installed and serves as a second layer of defense against water penetration.

The traditional material for a weather barrier is building felt. Considering the relatively low material cost of felt, it is recommended to invest in heavier grades, double coverage, or both, to provide more robust performance, especially at shallower slopes.

Self-adhering (peel-and-stick) modified bituminous weather barriers provides an increased level of moisture protection. They are frequently used to seal seams and are flexible enough to form to complicated configurations. Self-adhering membranes are typically recommended at for use at edges, eaves, rakes, valleys, hips, ridges, crickets, and other difficult areas. It is important to consider that modified bituminous membranes are vapor barriers, and in cold or mixed climates their placement should be carefully designed to avoid trapping moisture in the roof assembly.

Slip sheets are necessary under metal roofs to keep them from sticking to the felt weather barrier. Some modified bituminous membranes may come with a surfacing that can be used under metal roofing

Ice dams are a problem for many shingle roofs in cold climates. The first defense against ice dams is to detail the roof framing to allow full thickness of insulation to the edge of the roof, and proper venting to ensure that the roof deck stays cold. Additional protection can be provided by installing a modified bituminous membrane at eaves and up the roof surface past location of building wall.

ROOF DECK

Roof decks under steep slope roofing are almost always plywood or oriented-strand board (OSB) panels. Proper installation of the panels, especially spacing between panels to allow expansion without telegraphing through the shingles, is important.

In some commercial construction, steep slope roofing may be installed over metal decking or, occasionally, concrete planks. In these cases, board insulation is typically installed over the metal or concrete deck, and a nailable panel is added over the insulation. Up to slopes of 6 in 12, the panels may be simply screwed through the insulation layer. With steeper slopes, it may be necessary to install wood sleepers to avoid pulling the fasteners downslope, depending on the weight of the roof covering and the thickness of the insulation.

FLASHING

Flashing is an additional component of steep slope roofing assemblies used at edges, transitions, and penetrations, to provide a watertight assembly. Flashing has traditionally been sheet metal, but elastomeric sheets are replacing some sheet metals for the purpose of flashing, particularly at penetrations. Sheet metal, especially when installed in long lengths, must be allowed to expand and contract independent of the roof deck and the roof cov-ering. Running lengths of sheet metal should be installed with clips and not directly nailed. Where flashing is installed at points that interrupt the flow of water, it must be carefully detailed to control and redirect the water. Crimped dams at valleys and folded crickets are two examples.

COMMON STEEP SLOPE ROOF SHAPES

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LOW SLOPE ROOFING

Low slope roofing is generally designated as roofing with slopes at or less than 3 in 12. Low slope roofing is typically composed of a continuous waterproof membrane. Low slope roofs are not flat; most have a minimum slope of 1/4 in. in 12. Many low slope roof assemblies can be installed at slopes from 3 in 12 up to vertical in accordance with manufacturers’ recommendations. Low slope roofing is typically designed as a compact “warm” roof design, with insulation between the roof covering and the structural deck and with no ventilation.

Consult the following reference:

• NRCA Roofing and Waterproofing Manual

CHARACTERISTICS AND CONSIDERATIONS

Low slope roofing provides long-term performance at competitive costs and a platform for roof-mounted HVAC and window cleaning equipment. Low slope roofing is relatively easy to maintain and replace on tall buildings. This is no panacea, however, as metal roofing will suffer equally from poor design and installation. With proper detailing and installation low slope roofing assembly with can deliver 20 or more years of service with minimal maintenance.

Low slope roofing consists of five major components: the roof covering, the insulation with a cover board, a vapor barrier (if present) and sheathing to support the vapor barrier over metal deck; the structural roof deck, and flashing at the edges, transitions, and penetrations: Everything above the roof deck constitutes the roofing system.

TYPICAL LOW SLOPE ROOF ASSEMBLY

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INSULATION

Roof insulation not only reduces the energy required to condition the building, but it also helps to control condensation, provides a smooth substrate for the roof membrane, and can be used to slope the surface for drainage.

The ideal low slope roof insulation would be compatible with the membrane, adhesives, and substrates; be dimensionally stable and strong enough for anchorage, uplift, traffic, and impact; be fire-resistant; have a high and stable thermal value; and not be affected by moisture. No single material embodies all of these attributes, however, so the use of two or more layers with complementary properties is recommended.

• Polyisocyanurate foam: This is one of the most common commercial roof insulation boards. It is fire- and moisture-resistant, compatible with nearly all membranes and adhesives, and has excellent thermal properties. A more rigid cover board is recommended. Use the more conservative, aged R-value to evaluate long-term thermal performance.

• Polystyrene foam: Both extruded and expanded types are available. Polystyrene has a very high R-value and is unaffected by wetting; however, it is combustible and may require an weather barrier of gypsum board to comply with building codes. Moreover, polystyrene is difficult to install with hot asphalt adhesives and may not have sufficient rigidity for mechanical fasteners. Nevertheless, it is very commonly used in ballasted systems and inverted roof membrane assemblies (extruded type). A cover board is recommended to isolate asphalt-based membranes. Polystyrene foam may be recycled.

• Perlite: Manufactured from expanded minerals and binders, perlite insulation is noncombustible and has moderate thermal resistance, good strength, and excellent compatibility with most roofing materials. The perlite will absorb moisture.

• Wood fiberboard: Manufactured from wood or cane fibers and binders, wood fiberboard shares many traits with perlite. Its disadvantages are that it can burn and degrades when wet.

• Insulating concrete: Portland cement or gypsum with lightweight aggregates (possibly with foaming agents), and usually supplemented with expanded polystyrene, provide strength, thermal resistance, and no gaps, and readily produces a sloped, finished surface. Density is between typically between 20 and 40 psf. The system inherently introduces moisture into an assembly that should be dry, thereby creating an opportunity for trapped moisture and resulting failures. Venting of the completed assembly is recommended, which may affect the interior ceiling plenum and create leaks. Careful control of the drying time before installation must be maintained while also protecting the insulating concrete from precipitation.

• Gypsum sheathing: While not technically insulation, gypsum sheathing is a high-quality cover, providing a strong substrate for attaching the roof membrane, which is both fireproof and resistant to moisture. Pre-primed boards are available for hotasphalt applications.

• Miscellaneous boards: Other types of insulation include cellular glass, fibrous glass, mineral fiber, and others used for specialized applications.

• Composite Boards: Composite boards that combine two insulation materials laminated into one board are available; commonly polyisocyanurate or polystyrene foam bonded to plywood, OSB or gypsum sheathing.

Insulation should be installed in at least two layers, with joints offset between the two. The offset joints reduce air leaks that waste energy and could result in condensation on the cold underside of the membrane.

Insulation is mechanically fastened, set in adhesive or hot asphalt, or ballasted. It is preferable to not have mechanical fasteners extend through the entire assembly to the bottom of the roof membrane because the anchors may puncture or abrade the membrane. Therefore, limit mechanical fasteners to the bottom layer of insulation and install subsequent layers with adhesive.

Also, it is best to limit the size of insulation boards to 4 ft by 4 ft to reduce the size of cracks that may develop from shrinkage. Tapered insulation can be used to build up the roof slope and crickets.

Provide a cover board over the insulation if the top layer is not a composite board or lightweight concrete. Cover boards are typically gypsum sheathing, perlite, or wood fiberboard, to provide the physical rigidity and strength that most insulations do not possess. The cover board can count as the second layer of insulation.

WATER VAPOR CONTROL

Water vapor moves through low slope roof assemblies under two methods: air leakage and water vapor diffusion. Just as in walls, air leakage can carry much more moisture than diffusion. Use offset joints in multiple layers of foam insulation and air seals at edges and penetrations to limit the flow of cold interior air to the underside of the membrane, where it will likely condense. For buildings in cold climates with high interior winter humidity, the vapor drive may be strong enough that a vapor retarder on the warm underside of the insulation may be required, in addition to air sealing.

Additional water vapor control recommendations include:

• Most roof membranes are also vapor retarders, so adding a separate vapor retarder on the inside face may trap moisture in the insulation. Therefore, avoid a separate vapor retarder, unless it is actually required.

• The NRCA recommends a vapor retarder over concrete decks to protect the roof system from the effects of latent moisture.

• An inverted roof membrane assembly places the roof membrane on the warm side of the insulation and, therefore, is an ideal system for control of water vapor in cold climates.

• Vapor retarder membranes can be two- or three-ply built-up roofing, modified bituminous membranes, self-adhering peel-and-stick membranes, polyethylene sheets, or aluminum foils. It is best to select a membrane that will seal around mechanical anchors, or even better, select a membrane over which all sub-sequent layers of the assembly can be set in hot asphalt or other adhesive.

LOW SLOPE ROOF ASSEMBLY WITH VAPOR RETARDER

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• On a metal deck, a weather barrier board of gypsum sheathing or a thin layer of insulation may be required to provide a smooth substrate for the installation of the vapor retarder, although some membranes can be installed directly on metal deck.

• At the perimeter of roof vapor retarder, it may be best to connect to wall air and vapor retarders. Otherwise, ensure that the vapor retarder at the perimeter keeps moisture out of the roof assembly. Detail penetrations to be vaportight, similar to details for the roof membrane.

ROOF DECK

Roof decks for low slope roof assemblies must support the gravity loads from snow, rain, and rooftop equipment, and must resist wind uplift loads that may be greater than the gravity loads. The deck also is frequently sloped to provide drainage, and must be stiff enough to ensure that deflection does not result in localized water ponding.

Metal deck, concrete, and plywood are the three most common roof deck materials, but other materials are available. Concrete and poured gypsum decks must be cured before installing roof covering.

FLASHING

LOW SLOPE ROOF ASSEMBLY DESIGN

Roof membrane manufacturers produce standards and recommendations for their roof assemblies. These standards will typically include details for standard conditions, such as penetrations, edges, and terminations. Modifications to these details, such as increased roof slope and the use of tapered edge strips at the base flashing can extend the service life of the roof and should be considered by the design professional.

Many assemblies have specific detailing, and installation procedures that are required to obtain a 20-year warranty. These details should be adhered to even if the warranty is not required. No single low slope roof assembly solution is appropriate for every roofing condition.

Design guidelines and recommendations include:

• Consider light-colored, highly reflective roofs, to reduce the heat island effect in cities and, in warm climates, energy costs for the building.

• Avoid gravel-coated or ballasted systems on buildings in high-wind areas where the stone may become projectiles, causing collateral damage by breaking out windows.

• Consider recycled material content, life span, reuse, embodied energy, distance to source, and other sustainable criteria.

• Consider planted green roofs to slow water runoff, reduce the heat island effect, and increase thermal performance.

ROOF SLOPE AND DRAINAGE

Positive drainage increases roof life and is mandated at 1/4 in. in 12 in most codes, although some large governmental and corporate owners require 1/2 in. in 12. All surfaces of the finished roof should be sloped sufficiently so that no ponding occurs 48 hours after a rain.

Design guidelines include:

• Consider deflection of deck, particularly at long spans. Deflection may be sufficient to negate the roof slope. If the deflection creates a low spot, ponding may increase the deflection, progressively increasing until failure. Structural engineers should check for this failure mode.

ROOF SLOPE SCHEMES

2.485

• It is typically less expensive to slope the roof deck and use tapered insulation to create crickets in small areas. If the roof deck is planned as a future floor and is flat, then tapered insulation should be used to build up the slope.

• In addition to primary drains, the roof must have provisions for secondary drainage. Overflow scuppers are the most reliable, but piped secondary drains are an option in most jurisdictions. Requirements for piped secondary drains may be include the size to be twice as large as primary to avoid clogging, or that the rainwater conductors discharge near an entrance so that building personnel will be alerted to the fact the roof is not draining properly. The height of the scupper and the resulting impounded water should be checked against the structural capacity of the deck.

WEATHER BARRIER

The roof system frequently also functions as the weather barrier on the top of the building. Roofs over concrete roof decks may function as a weather barrier, but the roof membrane or a vapor barrier is more frequently chosen as the air barrier. Some manufacturers will not warrant their membrane when it is to be used as an air barrier, particularly mechanically fastened single-ply membranes.

WIND SPEED

Wind speed is the primary determinant of the uplift forces acting on a roof, ASCE 7, “Minimum Design Loads for Buildings and Other Structures,” and Factory Mutual Global (FMG) Loss Prevention Data Sheet, “Wind Loads to Roof Systems and Roof Deck Securements” both provide site maps with historical gusts. Adjustments for terrain, building height, parapets, wall openings, and hurricane exposure will result in an uplift classification. Note that wind speeds in miles per hour (mph) and uplift values in pounds per square foot (psf) often are very similar, but should not be confused. The uplift value applies to the field of the roof. Perimeter zones and corner zones have increased uplift, typically at 1.5 and 2 times, respectively, of the field value.

COOL ROOFS

Lightly colored, reflective, and high-emissivity roof systems reduce cooling loads and heat island effect in urban areas. Refer to the ENERGY STAR listing at www.energystar.gov.

INSURANCE COVERAGE

Some owners’ insurance coverage (Factory Mutual Global is the most common) will place more stringent requirements on a roof assembly design than the building code or the membrane manufacturer. Verify requirements with the owner at the beginning of the roof design process and for compliance at each subsequent step. The primary impact of FMG is the use of higher design wind speeds, resulting in higher uplift loads on the roof assembly, including the roof deck and perimeter, and limitations on choices of listed materials and assemblies.

FIRE-RATED ROOF ASSEMBLIES

For most fire-rated roof assemblies, a Class A roof covering and listed insulation is acceptable, but verify with the roofing manufacturer and authority having jurisdiction. Note that unlike floor assemblies, penetrations through roofs do not need to be firestopped, except in portions of roofs where openings are not permitted (such as near firewalls).

ROOF EMERGENCY FALL PROTECTION

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FALL PROTECTION

An advantage of low-slope roofs is their use as a platform for maintenance of the facility, which may include roof mounted equipment or equipment used for maintenance of windows and walls below the roof. Verify code requirements and related equipment requirements. Other protection recommendations include

• Use of warning signs and locks at roof access points.

• Use of emergency fall-arrest anchors. A worker should be able to tie off a line to a safety harness and be able to access the entire roof edge without being exposed to an excessive fall. Consultants and manufacturers are available to assist in design. Refer to OSHA and local regulations for worker and windowwasher safety requirements.

• Provide a continuous cable on structural post supports around the perimeter of the roof and approximately 10 ft back from the edge. The cable allows workers to tie off their safety harnesses at any point. The cable also serves as a physical warning that a worker is approaching the edge of the roof; signs can be added with further instructions.

• Provide fall-arrest anchors, which can be posts mounted on the roof or “eyes” mounted on penthouse walls. Spacing of the anchors should be determined by projecting a 30° cone and ensuring total coverage of the perimeter. Provide additional anchors around obstructions.

• Note that emergency tie-offs are also required for workers on window-washing staging.

WARRANTIES

Roofing manufacturers offer warranties, ranging from a two-year material-defect-only coverage to no-dollar-limit (NDL), 20-year full system replacement.

Some products are promoted as having extremely long warranty periods, but they lack in-place proven performance to back up these claims. Design professionals should read the warranty provisions carefully and not rely too heavily on the warranty as a basis for product selection.

Note that warrantable roof assemblies and details reflect a compromise chosen by the manufacturer between dependable service and a low initial cost, to remain competitive in the open market. Therefore, do not automatically assume that the offer of a warranty implies the highest quality.

Consult the following references:

The NRCA Roofing and Waterproofing Manual; (National Roofing Contractors Association, 2006)

Roofing Design and Practice (Pearson Education, 2000), Stephen Patterson and Madan Mehta.

NOTE

2.485 Slopes can be accomplished with tapered insulation on flat roof decks.

ROOF COVERINGS

STEEP SLOPE ROOF COVERINGS

WOOD SHINGLES AND SHAKES

Wood shingles and shakes are cut from wood species that are naturally resistant to water, sunlight, rot, and hail (i.e., red cedar, redwood, and tidewater red cypress). They are typically installed in the natural state, although stains, primers, and paint may be applied.

Nails must be hot dipped in zinc or aluminum. Nail heads should be driven flush with the surface of the shingle or shake but never into the wood.

Weather barrier and sheathing should be designed to augment the protection provided by the shingles or shakes, depending on roof pitch and climate. A low-pitched roof subject to wind-driven snow should have solid sheathing and an additional weather barrier.

Use self-sealing peel-and-stick modified bituminous membrane weather barrier at eaves valley, rake, and other detail areas. Modified bituminous weather barrier is a vapor retarder, so is it not recommended for continuous application where the weather barrier needs to breathe.

WOOD SHAKES APPLIED TO EXISTING ROOF

2.487

RED CEDAR HAND-SPLIT SHAKES

2.488

RED CEDAR HANDSPLIT SHAKES

2.489

RED CEDAR SHINGLES

2.490

NOTES

2.487 Shakes can also be applied over an existing wall or roof. Brick or other masonry requires vertical frame boards and horizontal nailing strips. Nails should penetrate sheathing or studs. Over wood, apply shakes directly, as on new sheathing.

2.488 Copper flashing should not be used with red cedar.

Contributor:

Richard J. Vitullo, AIA, Oak Leaf Studio, Ceoqnsville, Maryland.

UNDERLAYMENT AND ROOF SHEATHING

2.491

FANCY BUTT RED CEDAR SHINGLE SHAPES

2.492

SCHEDULE OF UNDERLAYMENT

2.493

SLOPE	TYPE OF UNDERLAYMENT
Normal slope: 4 in 12 and up felt	Single layer of 15 lb. asphalt saturated over entire roof
Low slope: 3 in 12 to 4 in 12	Two layers of 15 lb. asphalt saturated felt over entire roof

APPLICATION OF UNDERLAYMENT ON STEEP SLOPE ROOFS

2.494

EAVE FLASHING

2.495

SCHEDULE OF ASPHALT AND COMPOSITION SHINGLE TYPES^a

2.496

NOTES

2.492 Fancy butt shingles are 5 in. wide and 7-1/2 in. long, and customproduced to individual orders.

2.495 Eave flashing is required whenever the January daily average temperature is 30°F or less or where there is a possibility of ice forming along the eaves.

2.496 a. For all designs, exposure, 5 in.; edge lap, 2 in.

b. More than one thickness, for varying surface texture.

c. Many rated as wind-resistant.

d. All rated as wind-resistant.

Contributors:

Richard J. Vitullo, AIA, Oak Leaf Studio, Crownsville, Maryland; Robert E. Fehlberg, AIA, CTA Architects Engineers, Billings, Montana.

SHINGLE APPLICATION DIAGRAMS

2.497

NAIL TYPES

2.498

NAILING OF SHINGLES RECOMMENDATION

2.499

DECK TYPE	NAIL LENGTH
1″ wood sheathing	1-1/4″
3/8″ plywood	7/8″
1/2″ plywood	1″
Reroofing over asphalt shingles	1-3/4″

SPANISH TILE

2.500

TILE ROOFING

FLAT INTERLOCKING TILES

2.501

Tile roofs can make a long-lasting, durable roof if well detailed and constructed. Roofing tiles are available in either clay or concrete and in a large number of profiles, sizes, colors, and textures. All tiles absorb moisture and, generally, the more porous, the less strong and durable the tile. Concrete tile is generally more porous than clay, and may require a sealer. The sealer may require reapplication that is inconsistent with tile’s otherwise durable quality. Typical 1/2-in. thick tiles weigh approximately 10 psf, with proportional increases for thicker tiles.

Tile is made from two basic materials, clay and concrete:

• Clay: Clay tiles are formed from natural material, so color uniformity is dependent on the uniformity of the raw clay—unless glazed. Unglazed tile weathers only slightly over time. Glazed tiles are available in a larger number of colors, including bright blues, greens, reds, and oranges.

• Concrete: Concrete tiles are pressed in molds under high pressure. The synthetic oxide compounds color the surface. Tiles are sometimes painted, which may fade with time.

PROFILES

Tiles are typically available in three profiles, flat, are also called mission tiles.

• Flat: These are sized approximately 10 by 13 up to 13 by 20 in. Flat tiles may be very simple, requiring a doubled shingled overlap, or may be interlocking, with approximately a 3-in. head overlap. Tiles may be fluted on the back to reduce weight, or lugged to hang on battens.

• Barrel: Barrel tile sizes are typically 16 by 8, 19 by 10, or 18 by 12 in., punched for one hole.

• S-shaped: These tiles are approximately 10 by 13 up to 13 by 20 in. S-shaped tiles are essentially the pan and cover portions of barrel tiles in one piece.

INSTALLATION

• Underlayment: Tile roofs in areas of high rain or wind driven rain are likely to allow some water under the tiles and the underlayment provides the final defense against water intrusion. Therefore, the underlayment must be more robust and detailed more thoroughly than in some other steep roofing systems. The minimum underlayment is a double layer of No. 30 unperforated

Contributor:

Robert E. Fehlberg, FAIA, CTA Architects Engineers, Billings, Montana; Darrel Downing, Rippeteau Architects, PC, Washington, DC.

asphalt saturated felt except single coverage allowed at slopes over 20:12. In comparison to the cost of the tiles, the felts are inexpensive; consider using heavier No. 45 or 60 felts. For all edges and detail areas, such as eaves, valleys, rakes, crickets, it is recommended that you install self-sealing, peel-and-stick modified bituminous underlayment. The modified bituminous membrane provides an additional level of protection by sealing around the nails and stopping migration of water under loose felts. Self-sealing membrane is especially important for protection against ice dams in cold climates. Modified bituminous membranes are vapor retarders and should not be used across the entire roof substrate if a continuous vapor retarder is not desired.

• Flashing: Sheet metal flashing embedded in the tile should be minimum 24 oz. copper or lead-coated copper or 26-gage stainless steel, fabricated to allow differential thermal movement.

• Wood nailers: Although the simplest and least expensive method to install tiles is to nail them directly to the wood deck, nailers can help secure the tiles and provide drainage. For tiles with lugs, horizontal battens with a 1/2 in. space every 48 in. is recommended. Mission tiles may require vertical nailers of 2 by 3’s or 2 by 4’s, spacing to suit tiles plus nailers at ridges and hips. For maximum reliability and long-term performance it is recommended that you install vertical nailers at 24 inches on center with horizontal nailers to suit the tiles. This lattice arrangement allows maximum drainage and drying below tiles. Nailers should preservative treated.

• Tiles: Barrel tiles are typically secured with a single nail each. Flat and S-shaped tiles typically are installed with two nails. Nailing may be reduced in the field of the roof depending on slope and wind conditions; verify with local code. Some tiles, especially barrel tiles are laid in cement.

• Low-slope tile roofing: Tile roofing may be used in some areas of limited rain and wind at slopes lower than 4 in 12, if the lattice nailer system is installed over a continuous waterproof membrane of double-layer modified bituminous roofing. The tiles basically shield the membrane roofing (which provides the actual waterproofing) from UV exposure.

• High-wind areas: For high-wind areas, refer to The Concrete and Clay Tile Installation Manual, published by the Florida Roofing, Sheet Metal, and Air Conditioning Contractors Association and the Roof Tile Institute.

SLATE ROOFING

Slate roofs are extremely durable, sometimes lasting 75 or 100 years. Due to the expense and durability of the slates, it is important to select all supporting and accessory materials for a similar life span. Use the following as selection guidelines:

• Commercial standard: The quarry run of 3/16-in. thickness; includes tolerable variations above and below 3/16 in.

• Textural: A rough-textured slate roof with uneven buts. The slates vary in thickness and size, which is generally not true of slate more than 3/8-in. thick.

• Graduated: A textural roof of large slates. Greater variation in thickness, size, and color.

• A square of roofing slate: A number of slates of any size sufficient to cover 100 sq ft with a 3-in. lap. Weight per square: 3/16 in., 800 lb; 1/4 in., 900 lb; 3/8 in., 1100 lb; 1/2 in., 1700 lb; 3/4 in., 2500 lb.

• Standard nomenclature for slate color: Black, blue-black, mottled gray, purple, green, mottled purple and green, purple variegated, and red. These should be preceded by the word “Unfading” or “Weathering.” Other colors and combinations are available.

• Durability: Durability of slates is rated for their expected service life according to ASTM C 406 as: S1 for over 75 years, S2 for 40 to 75 years, or S3 for 20 to 40 years.

• Weather barrier: The minimum weather barrier is a single layer of No. 30 un-perforated asphalt saturated felt with double coverage up to 20 in 12 slopes. Use No. 45, 50 or 60 felts under textural or graduated slates. In comparison to the cost of the slates, the felts are inexpensive; consider using heavier No. 45 or 60 felts. For all edges and detail areas, such as eaves, valleys, rakes, crickets, it is recommended that you install self-sealing, peel and stick modified bituminous underlayment. The modified bituminous membrane provides an additional level of protection by sealing around the nails, stopping migration of water under loose felts, and is especially important for protection against ice dams in cold climates. Note that the modified bituminous membrane is a vapor retarder, and it should not be used across the entire roof substrate if a continuous vapor retarder is not desired.

NOTES

2.502 a. In climates where snow and ice buildup occurs, valleys should be avoided.

b. Building felt laps over valley flashing.

Contributors:

National Roofing Contractors Association, Rosemont, Illinois; Grace S. Lee and Darrel Downing, Rippeteau Architects, PC, Washington, DC; Domenic F. Valente, AIA, Architects & Planners, Medford, Massachusetts.

TILE ROOFING DETAILS

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SADDLE RIDGE

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• Nail fastener: Use large-head, hard copper wire nails, cut copper, cut brass, or cut yellow metal slating nails. Each slate punched with two nail holes. Use nails that are 1 in. longer than thickness of slate. Cover all exposed heads with elastic cement. In dry climates, hot-dipped galvanized nails may be used.

• Flashing: Sheet metal flashing embedded in the slates should be minimum 20 oz. copper or lead-coated copper, fabricated to allow differential thermal movement.

• Imitation slates: Slates manufactured from recycled tires, mineral fiber, portland cement, and a variety of other proprietary materials are available, generally at a lower cost than true slate. However, the appearance varies greatly and is rarely the same as true slate, and the expected service life is not as long.

DIAGRAM OF PROPER LAP FOR RISE/RUN

2.504

SADDLE HIP

2.505

BOSTON HIP

2.506

MITERED HIP

2.507

OPEN VALLEY

2.508

Contributor:

Domenic F. Valente, AIA, Architects & Planners, Medford, Massachusetts.

EAVE

2.509

SLATING CLIPS

2.510

WOOD RAFTER TO RECEIVE SLATE

2.511

METAL DECK TO RECEIVE SLATE

2.512

ROOFING SLATE

2.513

COMPOSITE ROOFING TILES

Fiber cement, cement wood, galvanized steel with acrylic coating, and ceramic slate roofing tiles are popular alternatives to clay or concrete roofing tiles. These composite tiles have been designed to be lighter, stronger, and easier to install than traditional, “natural” tiles. Their strength and combination of materials make them more fire-retardant and wind-resistant than conventional tiles.

Underlayment is similar as that required for asphalt shingles.

MINERAL-FIBER CEMENT

Mineral-fiber cement tiles combine organic fiber with cement, silica, water, and other additives. The resulting product is a roof slate that is lightweight, strong, versatile, and easy to install. The tiles can be made in a variety of distinctive shapes, colors, and textures that mimic natural materials such as slate and patterned wood shingles. Mineral-fiber cement tiles resist deterioration and moisture penetration, and are immune to pests and fungal growth. They are well suited for coastal regions and other areas with high humidity.

Mineral-fiber cement tiles should be applied to nailable decks only. For plywood decks with rafters spaced 20 in. or less, the plywood should be at least 1/2 in. thick. If rafters are spaced greater than 20 in., 5/8 in. plywood is recommended. To fasten, use standard 1-1 /2 in. galvanized 11-gauge flat-head roofing nails with 3/8 in. heads. Flashing should be of a noncorrosive metal not lighter than 28 gauge.

When wood fibers are used the tiles are lightweight and can be used for reroofing as well as for new construction. They have excellent impact resistance and are easily sawn and nailed. As a richly textured, composite product, mineral-fiber tiles create an aesthetic similar to that of heavy cedar shakes, yet provide the fire protection associated with cementitious products. The portland cement is noncombustible and allows for Class A fire ratings, and the wood fibers provide excellent tensile strength and a light weight when compared to standard concrete tiles.

NOTES

2.510 Stainless steel clips properly space slates, allow movement, and eliminate nailing through slate and associated problems of broken slates caused by improper nailing.

2.512 a. Where slope exceeds 8:12, it is recommended that you add wood sleepers between insulation to support plywood.

b. In hot climates, the weather barrier may need to also be a vapor retarder.

Contributor:

Domenic F. Valente, AIA, Architects & Planners, Medford, Massachusetts.

CEMENT WOOD TILES

2.514

CERAMIC SLATE

Ceramic slate tiles combine the look of natural slate with the firedin strength and durability of ceramic tile. These tiles have the thickness, texture, and appearance of older slate but at a fraction of the weight and cost. They are impervious to freeze-thaw cycles, fire, moisture, and efflorescence.

METAL ROOFING TILES

The advantage of metal roofing tiles over traditional clay or concrete tiles is that they are lightweight, easier to handle, and quicker to install, and because they require fewer building components, they are less costly. Minimum recommended roof pitch for use of metal roofing tiles is a slope of 3 in 12. Roofs with shallower slopes require sealant in all side laps.

Metal roofing tiles usually come in sheets and have a base material of roll-formed 24- to 26-gauge painted galvanized or Galvalume steel. First, a layer of crushed and graded stone granules is bonded to the steel panels with an acrylic resin formula, and then a clear acrylic glaze is applied. Slow oven curing completes the process, and the underside of the tile is protected with a final coat of polyester paint.

Panels can be installed quickly and are secured to either wood or steel battens, creating a strong, weatherproof construction. The panels can be installed directly over existing roofs, unlike clay or concrete tiles, and are thus ideally suited for retrofitting roofs.

METAL ROOFING TILES

2.515

METAL ROOFING TILES AT PITCH CHANGE

2.516

METAL ROOFING TILES DETAILS AT EAVE AND RIDGE

2.517

NOTES

2.516 When an equal number of full courses cannot be accommodated at the pitch change, a full panel can be bent to suit. When the roofline changes dramatically, install a batten at the pitch change.

2.517 The fascia must be positioned above the roof deck sheathing or rafters by the height of the batten. The fascia becomes the first panel batten.

Contributor:

Grace S. Lee, Rippeteau Architects, PC, Washington, DC.

BUILT-UP BITUMINOUS ROOFING

A built-up bituminous roofing assembly is composed of a base sheet attached to the roof substrate, two or more reinforcing felt ply sheets, and a surfaced cap sheet. Asphalt and coal tar are the primary bituminous materials used for built-up roofing. Coal-tar bitumen has a history of maintaining functional characteristics for a very long period, but there are some questions regarding safety from coal-tar fumes, and this is generally more expensive. As the heated mopping bitumen fuses with the saturating bitumen in the roofing felts, the layers are welded together. Surfacing include aggregate, minerals, protective or reflective coatings, and smooth surface. Built-up bituminous roofing can be a very durable and high-quality roof, but requires more skill to install than some other assemblies. If the owner is willing to invest in frequent independent inspection of the roof, then a BUR is an excellent choice.

Four types of asphalt and two types of coal tar are presently used as bitumen in built-up roofing assemblies. The grade of asphalt used for BUR systems should be appropriate for the slope of the roof. Backnailing of felts is recommended for built-up roofing whenever the roof slope exceeds 1/2 in. in 12. Aggregate-surfaced built-up roofing should not be used on slopes exceeding 3 in. in 12.

COAL-TAR TYPES

2.518

ASPHALT TYPES

2.519

BUILT-UP BITUMINOUS ROOFING—AGGREGATE SURFACE

2.520

Reinforcing felts for BUR may be saturated, coated, or impregnated with bitumen and are manufactured from both organic and inorganic materials. Organic felts are manufactured from the fiber of paper, wood, or rags. Saturated felts are saturated with asphalt or coal tar bitumen. Impregnated roofing felts are generally lighter in weight and termed “impregnated” because their surface is not completely covered (coated) with asphalt. Saturated and coated roofing felts are generally factory-coated on both sides and surfaced on one or both sides with fine mineral sand or other release agents to prevent adhesion inside the roll prior to application.

Prepared roofing felts have been saturated and coated with talc, mica, sand, or ceramic granules incorporated into the weather surface of the felts, both to provide weather protection and for decorative purposes. Reinforced flashing membrane consists of a glass-fiber base felt that is laminated with cotton, or glass-fiber fabric coated with asphalt. Rosin-sized sheathing paper is a rosincoated building paper generally used in built-up bituminous roofing to separate felts from wood roof decking.

BITUMEN TEMPERATURE

Proper application temperatures are vital to the creation of a quality built-up bituminous roofing assembly. Temperatures that are too high can lead to incomplete coverage, voids, and lack waterproofing qualities. Temperatures that are too low can lead to poor adhesion, high expansion properties, and low tensile strength.

Bitumen can be heated at high temperatures for short periods of time without damage; in fact, they must be heated at high temperatures to achieve complete fusion and strong bonding of the plies. There is an optimum viscosity range and an optimum temperature range at the point of application that allow complete fusion, optimum wetting and mopping properties, and the desirable inter-ply bitumen weight called the equiviscous temperature (EVT). Excessive and prolonged heating of asphalt and coal tar products may have a deleterious effect on the quality of the product.

BUILT-UP ROOF SURFACING

Surfacing protects the bitumen and felts of a built-up bituminous roof from direct sunlight and weather exposure, and may provide other properties such as fire-resistance or reflectivity. Surfacing types include aggregate, smooth surfacing, and mineral cap sheet.

• Aggregate surfacing: The aggregate in roofing serves as an opaque covering that improves the appearance and fire-resistance of the roof and helps resist premature aging and damage from weather, temperature fluctuations, and ultraviolet rays. Aggregate also increases the wind uplift resistance of the roof membrane and permits much heavier application of bitumen than would otherwise be possible.

• Smooth surfacing: Built-up bituminous roofing may be left smooth, surfaced with a top coating of hot asphalt. Smooth surfacing should not be confused with a built-up membrane left unsurfaced (exposed felts). Smooth surfaced built-up roofing should be specified only in those circumstances where aggregate-surfaced built-up bituminous roofing is impractical, such as when the slope of the roof surface exceeds 3 in. in 12, where the proximity of air-intake or exhaust equipment may cause loose aggregate, and where appropriate aggregate is not available

• Mineral-surfaced (cap sheet): Some areas of the country (particularly the far western and southern states) use mineral-surfaced cap sheets as the final surfacing for built-up roofing membranes. These assemblies are similar to aggregate and smoothsurfaced except that a final layer of roofing material with a finished surface is installed on top of the multi-ply roof assembly. This assembly is not popular in colder climates, primarily because it requires phased construction of the final layer of roofing material.

NOTES

2.520 a. If applied over wood sheathing, add rosin-sized sheathing paper between the sheathing and base bitumen sheet.

b. In lieu of asphalt, coal tar is an acceptable product.

c. For a more conservative system, specify four plies rather than three.

Contributors:

National Roofing Contractors Association, Rosemont, Illinois; Valerie Eickelberger, Rippeteau Architects, PC, Washington, DC.

ELASTOMERIC AND THERMOPLASTIC MEMBRANE ROOFING

Elastomeric membrane roofing and thermoplastic membrane roofing assemblies are both types of single-ply membrane roofing. Single-ply membrane roofing utilizes large sheets that are joined into a continuous roof membrane. In these assemblies the seams and flashing may be vulnerable to defects in workmanship, thus representing a primary weakness of the system. Single-ply membranes are also generally less resistant to physical abuse and cannot as easily be resurfaced as other types.

Single-ply membranes are available in two types: thermoset and thermoplastic. Thermoset materials cure during manufacture and can only be bonded at seams with adhesive. Ethylene propylene diene monomer (EPDM) is the most common thermoset membrane; chlorosulfonated polyethylene (CSPE) and polyisobutylene (PIB) are also available, but not as common. Thermoplastic membrane roofing materials are uncured and, therefore, are capable of being hot-air-welded or solvent-welded. Polyvinyl chloride (PVC) and thermo-plastic polyolefin (TPO) are the common thermoplastic membranes.

Single-ply membranes may be installed using three methods:

• Loose-laid ballasted assemblies: Loose-laid assemblies are the least expensive and require the least skills of the installer. There are, however, a number of disadvantages. First, membrane is susceptible to puncture from ballast when maintenance staff walks across the roof. Second, leaks are very hard to find because the water is free to travel horizontally within the insulation before appearing on the interior, and the membrane is covered with stones. Third, the loose ballast is problematic because it can be moved around on the roof by the wind, leaving some areas of the membrane unsecured, ballast may also fly off the roof as dangerous projectiles. Size and weight of ballast should be designed for the specific project site, with increased weights at perimeter and corner zones. Specially designed lightweight concrete roof pavers that are cast for use as roof ballast may be used in place of regular aggregate ballast for some or the entire roof, refer to Figures 2.654 and 2.723. Avoid ballasted roofs in hurricane areas and on high-rise structures. The ballast can be a light color, but is generally not as reflective as white single-ply membrane roofing.

• Fully adhered assemblies: Fully adhered assemblies are generally the most expensive of the three applications and offer the highest-level of performance. Fully adhered assemblies may use nonreinforced or reinforced sheets, which generally take longer to wear through. Leaks are relatively easy to find because an area of wet insulation usually forms immediately below the gap in the membrane.

• Mechanically attached assemblies: Membranes for mechanically attached assemblies should be reinforced to resist the tearing forces generated by uplift. Because a relatively large amount of seaming is required, thermoplastic sheets are becoming more popular. The level of difficulty of finding leaks within mechanically attached systems is between the loose-laid and fully adhered systems.

LOOSE-LAID BALLASTED SHEETS

2.521

Membrane sheets and insulation are laid loose with the membrane secured at the perimeter and around penetrations only. The membrane is then covered with a ballast of river-washed stones (typically 10 lb/sq ft) or appropriate pavers. This system works efficiently with insulation approved by the membrane manufacturer and on roofs with a slope not exceeding 2 in 12.

FULLY ADHERED SHEETS

2.522

Fully adhered membrane assemblies are not limited by slope, because the membrane is secured to the substrate with bonding adhesive and by mechanically fastening the membrane to perimeter and penetrations. This assembly is appropriate for contoured roofs and roofs that cannot withstand the weight of a ballasted assembly. The membrane can be directly applied to numerous types of roof deck surfaces including concrete and wood and may be compatible with insulation or protection board.

MECHANICALLY ATTACHED SHEETS

2.523

A mechanically attached roof assembly is appropriate for roofs that cannot carry the loads imposed by ballasted roof assemblies. Assemblies are available with fasteners that penetrate the membrane, or that require no membrane penetration. The membrane is anchored to the roof using metal bars or individual clips, and it may be installed over concrete, wood, metal, or compatible insulation.

EPDM ROOFING

Ethylene-propylene-diene-monomer (EPDM) membranes are typically 30 to 60 mils in thickness, single-sheet roofing materials. The membranes are available either nonreinforced or reinforced with fabric. Seams in the membrane are spliced and cemented. EPDM membranes are highly resistant to degradation from certain chemicals, ozone, and ultraviolet radiation, and have excellent resilience, tensile strength, abrasion resistance, hardness, and weathering properties.

EPDM membranes may be loose laid, mechanically fastened, or fully adhered to either nailable or nonnailable decks. For loose-laid systems, ballast provides resistance against wind uplift forces. Field application of surfacing or coatings may enhance the weather-resistance properties, or may be simply aesthetic. Terminations at roof edges, parapets, and other flashings utilize material identical to the roof membrane material shaped to conform to the substrate and area being flashed.

PVC ROOFING

Polyvinyl chloride (PVC) membranes may be nonreinforced or reinforced with glass fibers or polyester fabric the membranes are typically 45 to 60 mils in thickness Seams are sealed by heat or chemical welding, and may require additional caulking. PVC membranes are resistant to bacterial growth, industrial chemical atmospheres, root penetration, and extreme weather conditions. PVC membranes also have excellent fire-resistance and seaming capabilities.

ASTM D 4434 classes PVC materials into several types and classes, depending on the construction of the sheet material:

• Type I: Unreinforced sheet

• Type II, Class I: Unreinforced sheet containing fibers

• Type II, Class II: Unreinforced sheet containing fabrics

• Type III: Reinforced sheet containing fibers or fabrics

PVC membranes may be loose laid, mechanically fastened, or fully adhered to either nailable or nonnailable decks. For loose-laid systems, ballast provides resistance against wind uplift forces. Some PVC membranes have a factory-applied coating to enhance weather-resistance or aesthetics. Field application of the coatings may be an option and is dependent on the membrane manufacturer.

Contributors:

CTA Architects Engineers, Billings, Montana.

TPO ROOFING

Thermoplastic polyolefin (TPO) membranes are blended from polypropylene and ethylene-propylene rubber polymers, and may include flame retardants, pigments, UV absorbers, and other modifiers. Membrane sheets are available reinforced and unreinforced in thickness from 40 to 100 mils. TPO membranes range from stiff and “boardy” to soft and flexible. Seams are heat-welded and may require additional caulking to protect wicking of the reinforcing. TPO is resistant to animal fats, some hydrocarbons, and vegetable oils.

TPO membranes may be loose laid, mechanically fastened or fully adhered. Some membranes are white or light in color, or field coatings may be applied.

COATED FOAM ROOFING

Polyurethane foam roofing is spray-applied, seamless, and fully adhered. The foam is made by mixing isocyanate and resin components at a 1:1 ratio. Spray polyurethane foam is a closed-cell foam that provides good insulation and water resistance. These assemblies are used with a protective coating or stone ballast covering, which protects the foam from ultraviolet rays and mechanical damage.

These assemblies can be applied in varying thicknesses to eliminate ponding, to improve drainage, and to meet required R-values (approximately R-6.25 per inch). One advantage of coated foam systems is that they can be used over highly irregular surfaces, unusual geometries, or existing sloped metal assemblies. They are also inherently lightweight and offer good wind-uplift-resistance.

Keep the following in mind when working with coated foam roofing:

• Before sprayed polyurethane foam roofing is applied, all surfaces must be clean, free of contaminants, securely fastened to the substrate, and completely dry. Moisture-sensitive indicators may be needed to detect any moisture within the existing roof assembly. Vapor retarders may be necessary; consult with the manufacturer to coordinate a specific roofing condition with a foam application.

• Most polyurethane foam manufacturers produce three seasonal grades: winter (fast), regular, and summer (slow).

• During application wind may affect quality; use windscreens or discontinue application. The surface texture of sprayed polyurethane foam can vary because of wind, equipment adjustment, spray technique, and characteristics of the materials used. Foam that will be elastomeric-coated should have a smooth texture, resembling orange peel. For an aggregate covering, the texture should be no rougher than popcorn.

Protection of sprayed polyurethane foam falls into two general classifications: protective elastomeric coatings and aggregate. There are seven generic types of elastomeric protective coatings: acrylic, silicone, urethane, butyl, hypalon, neoprene, and modified asphalt. The physical properties of these coatings may vary, and the coating manufacturer should be consulted for recommendations on specific needs. Aggregate granules may be applied to the wet, uncured protective topcoat to enhance the resistance of the coating systems to UV or mechanical damage.

COATED FOAM ROOFING

2.524

SINGLE PIPE PENETRATION

2.525

FLUID-APPLIED ROOFING

Fluid-applied roofing assemblies may be applied at ambient temperatures or heated in kettles. Most of them have some sort of reinforcing fabric that is applied along with the liquid component. Fluid-applied roofing applied over existing roofs is not generally accepted as a “membrane,” but as a coating.

Acrylic latex and urethane are the two main types of cold liquid-applied roofing. Acrylic latex refers to a family of products that use water-based polymers and cure by water evaporation. Liquid-applied urethane roof coatings are chemically cured to form an elastomeric membrane. Because these coatings are applied as liquids, installation is relatively simple, even for roofs with irregular geometries or multiple penetrations. For assemblies using a reinforcing fabric, a coating is applied to an acceptable surface. While the coating is still wet, a layer of polyester or fiberglass is laid into it, followed by an additional layer of coating. Subsequent layers may be added as desired or necessary.

Fluid-applied roofing is appropriate for new construction but is most commonly used as enhancements or for repairs to existing roofs, including modified bituminous roofs and built-up roofs.

The advantages of fluid-applied roofing are that it conforms very well to irregular surfaces, is easily applied, and comes in various colors. However, it is sensitive to the skills of the installer, and is best used in sloped roof situations.

HOT FLUID-APPLIED ROOFING

Most commonly, hot fluid-applied membranes are composed of rubberized asphalt applied at 150 to 210 mils in two coats with a reinforcing sheet between the layers. Although the membrane has limited puncture resistance, because it is most often applied directly to a concrete substrate and protected by insulation, puncture resistance is less critical. The membrane is self-healing to minor punctures, has crack-bridging ability, is relatively forgiving of rough substrates, and can be protected shortly after installation. Moreover, fluid-applied membranes allow for easier penetration flashing, so they are particularly suited to complicated roof shapes with many penetrations.

FLUID-APPLIED ROOFING

2.526

Fluid-applied roofing may also be used under board insulation and ballast for further protection.

FLUID-APPLIED ROOFING OVER EXISTING METAL ROOF

2.527

PROTECTED MEMBRANE ROOFING (PRM)

In a typical roofing assembly, the waterproof membrane (built-up, modified bitumen, or single-ply) is applied over the insulation, which is on top of the substrate and/or structural deck. The membrane in this situation is exposed to temperature extremes, as well as wear and tear from people walking or working on the roof. In a protected membrane roof (sometimes called the inverted or insulated roof membrane assembly, or IRMA), a layer of extruded polystyrene insulation board protects the membrane. Extruded polystyrene is the only material generally approved for this application because it does not absorb moisture. This roofing system is best used in extreme climates, where it is important to protect the membrane from the elements, or where the rooftop will receive heavy use (e.g., plaza or parking deck applications).

NOTE

2.527 Roof slope minimum is 1/4 in. in 12, or 2 percent; there is no maximum.

Contributors:

National Roofing Contractors Association, Rosemont, Illinois; Valerie Eickelberger, Rippeteau Architects, PC, Washington, DC; Richard J. Vitullo, AIA, Oak Leaf Studio, Crownsville, Maryland; Rich Boon, the Roofing Industry Educational Institute, Englewood, Colorado.

PROTECTED MEMBRANE ROOF SYSTEM

2.528

VEGETATED ROOFING

Varying approaches have been taken to vegetated roofing design, so-called green roofing. The type of assembly selected will depend in part on the job conditions, including climate, plant community desired, and load-bearing capacity of the roof deck. Green roof assemblies are compatible with both conventional and protected roof membrane (PRM) waterproofing systems. All assemblies will include the following characteristics:

• Protection of the waterproofing membrane from root and biological attach

• Protection of the waterproofing membrane from physical abuse and accident

• Base drainage layer

• Separation layer, to prevent fine-grained engineered soils from fouling or clogging the drainage layer system

• Engineered soil, to support the vegetation

Some waterproofing membranes do not require supplemental root protection. Assemblies 6 in. and thinner are referred to as extensive; assemblies 12 in. and thicker are referred to as intensive.

Optional components can be incorporated, among them:

• Irrigation

• Slope-stabilizing elements

• Root-reinforcement elements

• Enhancements to retain rainfall moisture

• Air layers to dehumidify the insulation layer (some PRM systems)

• Self-contained modules

• Ballasts to resist wind uplift

Most engineered soils intended for green roof use are manufactured from lightweight mineral aggregates. These materials typically have wet densities between 60 and 90 lbs per cu ft, measured according to ASTM E 2399.

Green roof assemblies can be classified into five categories:

• Category I: Single-layer assemblies usually installed with a fabric or foam mat to provide physical protection and improve drainage.The overall thicknesses of these assemblies are rarely greater than 4 in. These assemblies are associated with pitched roof installations. They also offer the least expensive option for roof greening.

• Category II: Two-layer assemblies in which the engineered soil is placed over an efficient geo-composite drainage layer. A common variation utilizes a drainage layer that can also retain some water. To reduce plant stress during drought conditions, the drainage layer should not be thicker than 1 in. Typical overall assembly thicknesses range from 3 to 6 in. These are probably the most commonly encountered extensive assemblies in the United States.

VEGETATED COVER SYSTEMS FOR ROOFS

2.529

• Category III: Two-layer assemblies in which a highly permeable coarse granular material is used to create the drainage zone. Typical overall assembly thicknesses range from 4 to 8 in. Compared to a Category II assembly of comparable thickness, a Category III assembly would be markedly more drought-tolerant and accommodate a broader plant selection.

• Category IV: Similar to Category III assemblies but with a deeper drainage layer to accommodate base (bottom-up) irrigation methods. The minimum thickness for this assembly is 6 in.

• Category V: These assemblies involve the use of a water retention panel that is filled with coarse granular material. As in the Category III and Category IV assemblies, a surface layer of engineered soil is placed over the granular layer and separated from it by a filter fabric. This assembly introduces an air layer at the bottom of the profile. The minimum thickness for this system is 6 in.

Category IV and V systems are irrigated and are most frequently associated with intensive applications. Irrigation enhances landscape design opportunities, and in warm climates can also enhance cooling effects. These assemblies are well represented in deep plaza landscapes that can support large perennial plants and trees.

CATEGORY III

2.530

CATEGORY V

2.531

NOTES

2.528 a. Ballast weight is a minimum of 10 lbs per square foot.

b. Refer to ANSI/SPRI/RMA RP-4 for wind design guidance.

c. In lieu of aggregate or concrete ballast, proprietary insulation boards with concrete topping are available. These boards weigh between 4.5 lbs per square foot and 10 lbs per square foot, depending on the product selected.

2.529 The air layer is a generally composed of a geocomposite drainage sheet.

Contributors:

Charlie Miller, PE, Roofscapes, Inc., Philadelphia, Pennsylvania.

ENVIRONMENTAL BENEFITS

Vegetated roofing provides three important environmental benefits. It:

• Prolongs the life expectancy of the underlying waterproofing materials, which will reduce waste generation and the amount of embedded energy associated with the roof.

• Restores a natural hydrologic balance to developed sites, including reducing flooding and promoting more effective water utilization by plants.

• Improves the energy performance of buildings.

The scale of the energy benefit will, of course, depend greatly on the climate; northern temperate and semitropical climates will benefit most. When selecting green roof systems, ask the following questions:

• What contained materials are manufactured from recycled materials or, alternatively, are recyclable?

• How durable is the combined waterproofing and green cover system likely to be? How can its longevity be enhanced?

• To what extent can irrigation be eliminated through appropriate selection of the engineered soil, system configuration, and plant selection?

SPECIAL CONSIDERATIONS

With appropriate precautions, vegetated roofs have been successfully installed in combination with all major waterproofing system types. These membranes do not require supplemental root-protection layers. Also, ASTM E 2397 provides a standardized procedure to established maximum combined assembly weights for use when determining dead loads.

A critical part of all vegetated roof design is protection for the drains and flashings that is comparable to that offered by the vegetated cover elsewhere. The flashing, in particular, are typically the weak link in the overall roofing assembly. As a result, it is considered good practice to armor flashings with metal counterflashing or to protect the flashings with “sacrificial” layers of membrane.

Green roof techniques have been employed with great success in Europe for more than 40 years. In most German cities, for example, vegetated roofing is an indispensable part of the country’s urban runoff management and water treatment strategies. Very effective methods for protecting underlying waterproofing membranes have been developed. Also, electrical techniques are available that make it possible to locate even small leaks with pinpoint accuracy.

Methods of installing plants include:

• Plugs

• Reinforced vegetated mats

• Seed and cuttings

• Modules planted in the nursery

Consult the following references:

• www.wbdg.org/designgreenroofs.php

• www.greenroofs.com

• www.greenroofs.org.

• Planting Green Roofs and Living Walls, by Nigel Dunnett and Noel Kingsbury (Timber Press, 2004)

• Green Roof Plants: A Resource Guide, by Edmund C. Snodgrass and Lucie L. Snodgrass (Timber Press, 2006)

METAL ROOFING

There are four types of metal roofing, in two major categories. The first category is the traditional metal roofing, which needs continuous structural deck support and is sometimes called architectural metal roofing. The second category is structural metal roofing, which is capable of spanning over open purlins. Structural metal roofing includes

• Standing seam

• Bermuda

• Batten seam

• Corrugated or formed sheet metal

STANDING SEAM ROOFING

Standing seam roofing may be installed on slopes as gentle as 1/4 in. in 12. Because of the architectural appearance of the roof system, it is more commonly used on steeper roof slopes, allowing the panels to be seen as part of the overall design.

STANDING SEAM METAL ROOF

2.532

PAN METHOD OF FORMING STANDING SEAM

2.533

FIELD METHOD OF FORMING STANDING SEAM

2.534

The spacing of seams may vary to suit the architectural style of the facility. Formed sheets (used with metal building systems) have seam spacing set by locations of punched holes in the structural framing members.

Two methods of forming a standing seam are used: the pan method and the roll method. In the pan method, the top, bottom, and sides of the individual sheets are preformed to allow locking together at each edge. Seams at the top and bottom of each sheet are called transverse seams. In the roll method, a series of long sheets are joined together at their ends with double flat-lock seams. These field-formed seams can be executed either manually or with a seaming machine (a wheeled electronic device that runs along the sheet joint forming the seam). In either method, cleats (spaced as recommended by the manufacturer) are formed into the standing seam. Seam terminations are usually soldered.

MOVABLE CLEAT

2.535

To allow for expansion and contraction movement in roof panels, some manufacturers set movable cleats into a stationary panel clip system, particularly for structural standing seam metal roofing. Note that the cleat must be anchored to a rigid substrate to limit rotation of the clip that constrains movement. If mounted over insulation, provide a layer of plywood or OSB board or provide the manufacturers’ large anchoring plate to distribute the load over a large area.

STRUCTURAL STANDING SEAM METAL ROOFING

2.536

Contributors:

Raso-Greanes, Ian Architecture Corporation, Waco, Texas; Straub Associates/Architects, Troy, Missouri; Emory F. Hinkel, Jr., Odell Associates, Charlotte, North Carolina; John A. Sculte, HOK, St. Louis, Missouri.

CORRUGATED OR FORMED SHEET METAL ROOFING

Sheet metal panels are formed from aluminum, galvanized sheet steel, Galvalume, and zinc. These are relatively low-performing systems relying on gaskets at exposed fasteners and minimal sealant to accommodate movement and remain watertight. A highly reliable weather barrier is preferred for best performance. The following requirements apply:

• Endlaps for roofing and siding must be at least 6 in. and fastened at every rib. Two fasteners may be required when designing for a negative (uplift) loading condition.

• Minimum sidelaps must be equal to one rib or corrugation and laid away from prevailing wind. Fasteners must be spaced a maximum of 12 in. o.c. for all types of roofing and siding.

• For roofing, fasteners may pierce only the high corrugation. For siding, fasteners may pierce either the high or low corrugation. Consult manufacturer for proper sheet metal fasteners and accessories.

• Minimum slopes for sheet roofing are: 1-in. depth corrugated—3 in 12; 1-1/2-in. depth ribbed—2 in 12; 1-3/4-in. V-corrugated—2 in 12.

METAL ROOFING—LOCKS AND SEAMS

The method for joining sheet metal depends on thickness of metal, anticipated movement, appearance, watertightness and cost. Refer to SMACNA for full information on balancing of all requirements.

CORRUGATED OR FORMED SHEET METAL ROOFING

2.537

ROOF DETAILING

• Elevate base flashing and penetration flashing above any standing water by using tapered edge strips. This detail is not required by most manufacturers but is a small amount of additional dependability.

• Provide crickets behind any interruption to the downhill flow of water such as at curbs, rails, and rooftop mounted equipment.

• Depress roof drains in large sumps approximately 3 to 4 feet square and minimum 1-1/2 inches deep using tapered insulation to ensure that there is no standing water at drains. In cold climates the underside of the drain body should be insulated with spray foam or else cold rainwater could cause condensation. The rainwater conductor should also be insulated, at least for a length sufficient to allow warming of drain water.

• Verify that roof decks and the adjacent parapet wall or penetrating element are supported together. If they are not, then the base flashing must be detailed to accommodate the anticipated movement.

• Heavy pieces of roof-mounted equipment may need to have curbs mounted directly on the structural frame of the opening or the flutes of metal deck may need to be blocked full to prevent crushing.

• Base flashing should be carried up and across the top of parapets and curbs if possible to ensure that water does not get behind the base flashing and under the roofing. If the wall includes an air barrier or water-resistant drainage plane, then connect base flashing to membrane.

• Pitch pockets should be avoided. Detail penetrations through the roof using square or round shapes that are nearly perpendicular to the plane of the roof.

• Detail lightning protection systems to provide adequate anchorage of air terminals and support of cables without penetrating roof membrane. Air terminals and cable at perimeter should be mounted to inside face of parapet or on coping. Air terminals in the field should be adhered to precast concrete pavers. Cable running across the field of the roof should be supported on traffic walkways or pavers. Cable laying on bituminous roof membrane will eventually become embedded in the softened membrane.

• Detail for replacement of the roof membrane. The membrane will need to be topped or replaced several times over the life of the building. It should be possible to install a new membrane under counterflashing and copings by removing and replacing the sheet metal without damage.

• Joints and fasteners in sheet metal flashing are notoriously susceptible to leakage after expansion and contraction. Back up sheet metal flashing with flexible membrane flashing.

• Expansion joints and area dividers should be detailed above the plane of the roof.

• Expansion joints should be specifically designed for the purpose and should have factory-fabricated intersections, tees, transitions and intersections. Joints made in the field should be simple, straight butt joints.

• Expansion joints fabricated from roof membrane do not maintain continuity of the expansion joint as well as factory-fabricated systems.

• Roof expansion joints must transition without leaks into vertical expansion joints in parapets and walls.

• Expansion joints should be provided with a second line of defense, usually of a watertight vapor barrier membrane. Systems are available with secondary drains.

• Area dividers are similar to expansion joints but do extend through the building structure. Area dividers are recommended at 200 to 300 feet centers, located at ells, tees, changes of deck span and other similar conditions where movement will damage the roof membrane. Note that many roof membranes are flexible enough to not require area dividers but the underlying coverboard and insulation are not flexible and allowing space for their thermal movement will prevent telegraphing of the substrate.

• Sources for Roof Details: A primary source for information regarding roof details is the NRCA Roofing and Waterproofing Manual, which covers most detail conditions for nearly every type of roofing system. NRCA details are nearly universally accepted. The second source for roofing details is the roof membrane manufacturer.

• Note however that the manufacturer will publish details that are selected to be less expensive, sometimes resulting in lesser performance. Pitch pockets are an excellent example. For more dependable details, review manufacturers data for details required for an extended 20 year warranty and compare against NRCA.

• Note that details from NRCA or the manufacturer need to be customized to suit the specific project conditions.

FULLY ADHERED ROOF AT PARAPET OR WALL

2.538

ROOF EDGE AT NONSUPPORTING WALL

2.539

METAL ROOF EDGE

2.540

FULLY-ADHERED ROOF SCUPPER

2.541

FABRICATED VENT PIPE FLASHING

2.542

ROOF DRAIN

2.543

ROOF DRAIN

2.544

EQUIPMENT CURB

2.545

AREA DIVIDER

2.546

PIPE SUPPORT

2.547

MULTIPLE PIPE PENETRATION

2.548

NOTES

2.544 a. Minimum 30 in. square, 2-1/2 to 4-lb lead or 16-oz soft copper flashing set on finished roof felts set in mastic. Prime top surface before stripping.

b. Membrane plies, metal flashing, and flash-in plies extend under the clamping ring.

c. Stripping felts extend 4 in. and 6 in. beyond edge of flashing sheet, but not beyond edge of sump.

d. The use of metal deck sump pans is not recommended 2.546 An area divider is designed simply as a raised insulated metal curb or double wood member attached to a properly flashed wood base plate that is anchored to the roof deck. Area dividers should be located between the roof’s expansion joints at 200 to 300 ft intervals, depending upon climatic conditions and area practices. They should never restrict the flow of water. Even though many single-ply roof membranes are flexible enough not to require an area divider, the insulation and protection board are not.

2.547 This detail allows for expansion and contraction of pipes without roof damage.

2.548 This detail illustrates another method of eliminating pitch pockets and a satisfactory method of grouping piping that must come up above the roof surface.

Contributors:

Valerie Eickelberger, Rippeteau Architects, PC, Washington, DC; National Roofing Contractors Association, Rosemont, Illinois.

SINGLE-PIPE PENETRATION

2.549

FLASHING AND SHEET METAL

Flashings is a thin material inserted in an assembly to direct the flow of water to the exterior. Flashing has traditionally been sheet metal, but modern elastomeric sheets are gaining in usage. Sheet metal flashing has traditionally been prone to leakage at joints. The joints can be soldered or welded, but this is not recommended for long lengths. In long lengths, joints have traditionally been waterproofed with sealant, but the joint design is not ideal and is also prone to fail. Therefore, it is recommended to back up the sheet metal flashing with a layer of an elastomeric membrane.

GUTTERS AND DOWNSPOUTS

Important notes regarding the design of gutters and downspouts are as follows:

• Continuous gutters may be formed at the installation site with cold-forming equipment, thus eliminating joints in long runs of gutter.

• Gutters and downspouts are available in aluminum, galvanized steel, copper, and stainless steel. Consult manufacturers for custom materials.

• Girth is the width of the sheet metal from which a gutter is fabricated.

• Although all joining methods are applicable to most gutter shapes, lap joints are more commonly used. Seal all joints with mastic or by soldering. Lock, slip, or lap joints do not provide for expansion.

• Expansion joints should be used on all straight runs over 40 ft. In a 10-ft section of gutter that will undergo a 100° temperature change, linear expansion will follow these coefficients of expansion (CE) and movements: aluminum: CE, .00128, movement, .15 in.; copper: CE, .00093; movement, .11 in.; galvanized steel: CE, .0065, movement, .08 in.

• Always keep the front of the gutter lower than the back.

• Use a minimum width of 4 in., except for canopies and small porches. The minimum ratio of depth to width should be 3 to 4.

• Many custom shapes for gutters and downspouts are available; consult manufacturers’ design manuals.

For more information on gutter sizing and details, refer to the Sheet Metal and Air Conditioning Contractors National Association (SMACNA) Architectural Sheet Metal Manual. For more on rainfall intensity, sizing of gutter, and sizing and spacing of downspouts, contact the Sheet Metal and Air Conditioning Contractors National Association (SMACNA).

TYPICAL GUTTER SHAPES AND SIZES

2.550

TYPICAL DOWNSPOUT SHAPES AND SIZES

2.551

GUTTER

2.552

PARTS OF A GUTTER/DOWNSPOUT ASSEMBLY

2.553

NOTES

2.549 a. Sheet lead minimum of 2-1/2 lb per sq ft. b. Minimum clearance of 12 in. from cant strips and other curbs or pipes.

2.551 a. Formed and extruded downspout sizes are 3 by 4 to 6 by 6; round sizes are 3, 4, or 5 in. diameter. (Extruded downspouts are for heavy traffic.)

b. Generally, space downspouts a minimum of 20 ft and a maximum of 50 ft apart.

c. A downspout of 7 sq in. minimum should be used, except for canopies or small porches.

d. Corrugated shapes resist breakage due to freezing better than straight profiles.

e. Elbows are available in 45°, 60°, 75°, and 90° angles.

Contributor:

National Roofing Contractors Association, Rosemont, Illinois; Valerie Eickelberger, Rippeteau Architects, PC, Washington, DC; Jones/Richards and Associates, Ogden, Utah; Lawrence W. Cobb, Columbia, South Carolina.

GUTTER PROTECTION

2.554

GUTTER HANGERS

2.555

GUTTER BRACKET OR STRAP SIZES (IN.)

2.556

NOTES

2.554 a. Gutters should be placed below the slope line, so snow and ice can slide clear. A steeper pitch requires less clearance.

b. Snow guards are installed on roofs to protect gutters from snow slides and snow overloading. They hold the snow in place evenly over the entire roof, allowing it to melt gradually into the gutter system. They also help prevent snow from collecting over the eaves, where it may thaw and refreeze, potentially causing damage.

c. Snow guard placement depends on the roof slope, local snow conditions, the insulation at the roof below, and the length of the rafters. Snow guards typically are staggered on the roof, with the first row starting 2 ft from the eave.

2.556 a. Gutter hangers are normally spaced 3 ft o.c.; reduce spacing to 1 ft-6 in. o.c. where snow and ice are prevalent.

b. Spike and ferrule hangers are not recommended if girth is greater than 15 in.

c. Hangers are available in many sizes, shapes, and materials, and are matched to the design of the gutter used. Consult manufacturers’ design manuals.

Contributors:

Jones/Richards and Associates. Ogden, Utah; Lawrence W. Cobb, Columbia, South Carolina.

FLAT ROOF DRAINAGE

The size and number of scuppers should be carefully determined to control ponding on roofs. Rectangular shapes convey more water (per inch of water depth on the roof) than round shapes. The performance of rectangular shapes approximates that of a broadcrested weir. Standard equations for channel flow are based on test models larger than typical roof scuppers. Downspout sizes normally are based on draining a given area of roof, but that flow rate may not pass through a scupper that has been sized to have a cross-sectional area equal to the downspout area.

The scupper sizing procedures are:

• Determine the head (H) in inches of water (typically 1 in. minimum by code) at a point 6 ft back from the scupper opening.

• Determine the roof drainage area in square feet (SF).

• Using rainfall intensity in inches per hour (IPH) from a rainfall data table, determine discharge capacity in gallons per minute (GPM). GPM = SF of roof area × IPH × 0.0104. The constant is 7.48 gallons per cubic foot divided by 12 in. per foot divided by 60 minutes per hour: GPM = (0.0104) IPH × SF.

• Using H and the GPM, find the aggregate scupper length (L) in the Scupper Capacity table (Table 2.699).

• Select enough individual scuppers to satisfy the total GPM requirement and locate them proportionately.

TYPICAL CONDUCTOR HEAD

2.558

SCUPPER AND CONDUCTOR HEAD DETAIL AT PARAPET WALL

2.557

OVERFLOW SCUPPER DETAIL AT PARAPET WALL

2.559

NOTES

2.559 a. Use overflow scuppers when roof is completely surrounded by parapets and drainage depends on scuppers or internal damage.

b. Precast concrete panels with scuppers do not need closure flanges on face; all penetrations should be seated.

Contributor:

Richard J. Vitullo, AIA, Oak Leaf Studio, Crownsville, Maryland.

SCUPPER CAPACITY IN GPM

2.560

COMBINATION SCUPPER AND GUTTER

2.561

Scuppers that empty into a gutter may be integrated with a roof edge. The scuppers are soldered into a formed gravel-stop fascia system. The suggested maximum scupper interval is 10 ft. The front rim of the gutter must be 1 in. below the back edge, and it should be below the nailers used to elevate the roof edge. The drip edge on the fascia should lap the back edge of the gutter a minimum of 1 in. The gutter must be free to move behind the fascia.

CHIMNEY FLASHING

STEPPED-PAN THROUGH WALL FLASHING

2.562

FLASHING AT RIDGE

2.563

FLASHING WITH CRICKET

2.564

ALTERNATE ONE-PIECE CRICKET

2.565

ALTERNATE ONE-PIECE BASE FLASHING

2.566

NOTE

2.562 Recommended for chimneys built of stone, rubble, ashlar, and any porous material.

Contributors:

SMACNA, Inc., Chantilly, Virginia; Grace S. Lee, Rippeteau Architects, PC, Washington, DC.

BASE AND COUNTERFLASHING AT FRAME WALL

2.567

BASE AND COUNTERFLASHING AT BRICK VENEER

2.568

BASE AND COUNTERFLASHING, WITH WALL AND ROOF DECK INDEPENDENTLY UPPORTED

2.569

COUNTERFLASHING DIAGRAM

2.570

SURFACE-MOUNTED COUNTERFLASHING

2.571

NOTES

2.571 Not for walls with internal drainage plain.

Contributors:

SMACNA, Inc., Chantilly, Virginia; Valerie Eickelberger, Rippeteau Architects, PC, Washington, DC.

ROOF OPENINGS

SKYLIGHTS

Skylights provide daylight to interior spaces and can reduce dependence on electrical lighting. In passive solar designs, skylights are used to admit direct solar radiation, enhancing space heating, and when vented properly, to induce convective airflow, reducing cooling loads through natural ventilation.

Skylights are available as units (which are shipped to the site ready to be installed) or as framed assemblies of stock components (which arrive fabricated for site assembly). Both fixed and hinged skylights are manufactured. The hinged variety can be opened manually or by remote control devices for venting. Frames are typically mounted on a built-up fabricated or site-built curb, with integral counterflashing; they can be assembled with or without insulation.

Self-flashing skylight units are available with or without curbs. Those without curbs are intended only for pitched roof assemblies and are not recommended for roof assemblies with finished spaces below.

Framed skylight assemblies are custom-designed by manufacturers to meet the necessary wind, roof, and dead loads of the assembly itself. When a skylight is pitched beyond a certain angle, it must be designed to resist environmental factors, as does a curtain wall assembly. Roof drainage for rainwater and storm water can limit skylight dimensions. Many skylights are face-sealed as a barrier system, but some are available as a pressure-equalized rainscreen system. Condensate gutters are needed in the body of the skylight assembly and around its perimeter. Gutters should be designed to evaporate collected water or be drained to the building plumbing system. Condensate drains through the skylight curb, common to many systems, violate the air barrier, resulting in energy losses and possible condensation.

Finishes for aluminum frame components are available as mill finish, clear anodized, duranodic bronze or black, acrylic enamel, and fluorocarbon.

In determining the desired form and size of the skylight unit/assembly, consideration should be given to:

• Environmental conditions, including orientation and winter and summer solar penetration angles at the site

• Prevailing wind direction and patterns

• Precipitation quantity and patterns

• Adjacent topography and landscaping (shade trees, etc.)

• Coordination with the HVAC system

PERCENTAGE OF ROOF AREA REQUIRED FOR SKYLIGHTING

2.572

• Use of shading, screening, or light reflecting/bouncing devices

• Views desired relative to view obstructions, streetlights

FRAMING, GLAZING, AND GASKETS

The heart of a well-designed skylight lies the detailing of frames, glazing, and sealant systems. The thickness, size, and geometric profile of all glass and acrylic glazing materials should be carefully selected for compliance with building codes and manufacturers’ recommendations. The following glazing materials are considered resistant to impact and breakage and are generally approved by codes (listed in descending order of cost):

• Formed acrylic with mar-resistant finish

• Formed acrylic

• Polycarbonates

• Flat acrylic

• Laminated glass

• Insulated glass units

• Insulated glass units have a laminated glass inner light and tempered or heat-strengthened outer light.

Framed skylights require somewhat greater mullion widths when glazed with acrylics in order to accommodate the expansion and contraction characteristics of plastics. For economy, tinted acrylics should be limited to 1/4-in. thickness. A combination fiberglass sheet and aluminum frame system with high insulating value and good light diffusion can be a cost-effective alternative. Domed acrylic glazing is almost self-cleaning, as the sloped shapes facilitate rain washing of the surface.

Gaskets are especially subject to degradation from solar ultraviolet rays. Excessive expansion and contraction of acrylic glazing can cause “rolling” of the gasket between metal framing. Small valleys created at the bottom of the sloped glazing and the horizontal glazing cap will hold water, which increases the chance of gasket breakdown and subsequent water infiltration.

SHADING AND GLARE CONTROL

Skylights can introduce too much uncontrolled light, especially in areas where video screens and computers will be used. Skylights also can allow excessive heat buildup. To mitigate these issues:

• Select extent of skylight, glazing, and shading devices to balance the gains of daylighting against heat gain.

• Select glass with low-E coatings, tint, reflective coatings, frits, or combinations to lower the solar heat gain coefficient.

• Approximately 40 to 50 percent visible light transmission in a skylight will appear as bright as vertical glazing with 60 to 70 percent visible light transmission.

• Shading devices such as louvers, grilles, and shades should be added to control direct sun. Movable systems, particularly if fully automated to track the sun are more effective than fixed systems, for controlling glare while maximizing daylighting.

DOME UNIT SKYLIGHT—FLAT ROOF

2.573

SECURITY AND SAFETY

Frames or screens to protect glazing from impact, fire, or forced entry may be designed into the skylight assembly. To avoid forced entry, a framed skylight should include deterrents to disassembling the framing, removing the snap-on cover, and melting the glazing (acrylics can easily be burned with a torch). Metal security screens may be required.

UNIT SKYLIGHTS

UNIT SKYLIGHT SECTION

2.574

NOTES

2.573 Glazing is typically clear, tinted transparent, or white translucent.

Contributor:

Richard J. Vitullo, AIA, Oak Leaf Studio, Crownsville, Maryland.

FLAT PANEL UNIT SKYLIGHT—SLOPED ROOF

2.575

FLAT PANEL UNIT—SKYLIGHT SECTION

2.576

FRAMED SKYLIGHT TYPES

Framed skylights are available in two different structural types, three glazing types, and two water management systems. Most manufacturers only provide systems in a limited number of the possible combinations.

STRUCTURAL TYPES, STRUCTURAL OR SKIN

• Structural skylights span the skylight opening and support all loads.

• Skin systems have a frame that performs glazing and waterproofing functions. They are applied to a separate structural system, typically of wood or steel. Skin systems frequently resemble structural systems, except that the members are much more shallow.

GLAZING TYPES

• Four-sided retained systems have pressure plates or other glazing stops on the full perimeter of each pane of glass. Glazing should be a wet/dry type or, preferably, a fully wet glazing for maximum reliability. Avoid systems (especially face-sealed systems) that use dry gaskets.

• Two-sided structural silicone-glazed (SSG) assemblies have pressure plates or glazing stops on the mullions that run parallel to the slope, and structural silicone glazing on mullions running across the slope. Because the SSG has no mullion cover above the plane of the glass, no water is trapped to cause potential leaks or stains from the evaporated water. Two-sided SSG systems are recommended for most framed skylights.

• Four-sided structural silicone glazed assemblies provide the advantages of two-sided SSG systems, plus a more streamlined appearance.

WATER MANAGEMENT SYSTEMS

• Face-sealed systems rely on a perfect watertight seal at the exterior face of glazing. Gutters and weeps on the interior side of the glazing are provided to control condensation only.

• Rainscreen systems employ redundant pressure-equalized rainscreen technology to control both air and water penetration. Drainage channels and weeps on the interior face drain not only condensation but also any minor leaks that get past the exterior seals. Although less common, PE rainscreen systems are more reliable.

POINT-SUPPORTED FRAMELESS SKYLIGHT SYSTEMS

• Frameless skylights supported on point glazing mounts are the most transparent and expensive skylights. They provide a nearly invisible separation between the interior and exterior. The systems rely on perfect silicone butt-joint glazing. The structural support can be one-way or two-way trusses of steel, aluminum, wood, laminated glass, tension cables, or combinations of these.

TYPICAL TUBULAR ALUMINUM FRAMING

2.577

RAFTER AND SIDEWALL DETAIL

2.578

NOTES

2.575 a. Clear and tinted transparent glass is typical, but tempered, laminated, and wire glass also are available.

b. Manual and powered vent operation, venetian blinds, shades, and exterior awnings are available. Consult manufacturers for available options.

Contributor:

Richard J. Vitullo, AIA, Oak Leaf Studio, Crownsville, Maryland.

PYRAMID FRAMED SKYLIGHT ASSEMBLY

2.579

CURB DETAIL AT SLOPED FRAMED ASSEMBLY

2.580

VERTICAL FRAME CURB DETAIL

2.581

DOUBLE-PITCH FRAMED SKYLIGHT ASSEMBLY

2.582

NOTE

2.582 Options for a pitched skylight include: (1) integration of skylight with roof structure at ridge, with slope of skylight to match slope of roof, and no end glazing; (2) hip end glazing; and (3) vaulted framing, with minimum rise at 22 percent.

Contributor:

Richard J. Vitullo, AIA, Oak Leaf Studio, Crownsville, Maryland.