MIL-HDBK-1001/5A
9.5 Ventilation. Ventilation is required in attic spaces between the steep-roofing framing and the ceiling to prevent condensation from forming on cold surfaces when warm, humid air flows upward from heated interiors or, in warm climates where it is simply entrapped in these attic spaces. Air movement prevents or alleviates condensation on under-surfaces of shingles, tiles, or roof decks and, therefore, prevents fungus rot of wood in the attic. Provide screened vents at eaves and gable ends to remove humid air. Ventilation also reduces roof temperatures, therefore prolonging membrane service life and, in cold climates,
preventing ice dam formations and snow slides. For cold region designs, consult U. S. Army, Cold Regions Research and Engineering Laboratory (CRREL), 72 Lyme Road, Hanover, NH 03755-
1290, to ensure good performance.
9.5.1 Vents. A minimum net free ventilation area of one square foot for every 300 square feet (28 square meters) of attic area is required. Ridge vents should be used whenever practicable, in conjunction with eave soffit vents. Ridge vents induce air-pressure differentials and accelerate air movement through the attic. In small gabled roofs without ridge vents, when the ceiling is applied to the bottom of the rafters, l-inch (25-millimeter) diameter holes should be drilled through the
ridge beam in every joist space to provide unobstructed transverse air flow to outside area.
9.6 Anchorage Techniques
9.6.1 Fasteners. Nailing types and sizes for different steep roofing materials are shown in Table 3. Fasteners should be corrosion resistant. For asphalt shingle fasteners, consult the ARMA Residential Asphalt Roofing Manual, or ARMA Asphalt Roofing With Staples Manual. Fastener requirements for clay and concrete tile vary with slope and wind design conditions. Wiring may also be required for anchoring of clay and concrete ridge tiles.
9.6.2 Special Anchorage. In addition to fasteners, anchorage of various steep roofing material requires other techniques. Lap cement is used at seams in asphalt roll roofing (side, end, ridge and hip strips). Asphalt shingles have self-sealing strips.
Clay and concrete tiles may require embedment in plastic cement. Plastic cement is often used to secure slate units at ridges and hips.
9.6.3 Anchorage in Hurricane or High-wind Zones. These require additional anchorage precautions. Clay and concrete tiles should be secured with special hurricane clips, additional
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