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.
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.
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.
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
Anchorage in Hurricane or High-wind Zones. These
require additional anchorage precautions. Clay and concrete
tiles should be secured with special hurricane clips, additional