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 MIL-HDBK-1001/5A
Section 9: STEEP ROOFING
9.1
Steep Roofing Description. Steep roofing comprises a
wide variety of roofing materials used on slopes exceeding 1-1/2
inches per foot (14 percent). Shingles, shakes, and tiles depend
on the gravitational-force component provided by slope to assure
positive water-shedding. The gravitational water shedding force
must exceed all the opposing forces (kinetic, capillary, and
atmospheric suction) tending to draw water up the slope between
overlapping roof units. A slope of 4 inches per foot (33
percent) is adequate for most steep roofing systems to assure
dependable water-shedding. When used on lower slopes (less than
1-1/2 inches per foot (14 percent)), steep roofing requires
additional measures to assure good performance.
9.2
Materials. Steep roofing materials including the
following: asphalt shingles, asphalt roll roofing, wood shingles
and shakes, clay and concrete tiles, metal, and slate. Consult
the NRCA Steep Roofing Manual, the SMACNA Architectural Sheet
Metal Manual, and the Asphalt Roofing Manufacturers Association
(ARMA) Residential Asphalt Roofing Manual for steep roofing
details.
9.3
General Design Requirements
9.3.1
Slopes. Minimum slopes for various steep roofing
materials are shown in Table 2. In snow country, designers
should consider hazards of sliding and drifting snow.
9.3.2
Decks. Structural plywood decks facilitate the most
convenient, economical, and dependable fastening techniques.
Other deck materials, such as concrete, require installation of
nailing strips, laths, horizontal battens, etc. These are
described in the NRCA Steep Roofing Manual.
9.4
Underlayments.
Several purposes are served by
underlayments:
a)
To keep the deck dry until shingles or tiles are
installed;
b) To provide secondary water resistance protection if
shingles or tiles are damaged, wind-lifted, or if wind-driven
rain or water behind ice dams at cold eaves ever penetrate beyond
the overlapped shingle;
c)
Form a cushion for slates;
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