01 May 1999
CONSIDERATIONS FOR STEEP ROOFING SYSTEMS
(Shingles, Shakes, Tile and Slate)
07310 (Slate Roofing)
07311 (Roofing, Strip Shingles)
07320 (Clay Tile Roofing)
8-1. STEEPLY SLOPED ROOFING SYSTEMS.
a. Overview. Watershedding roofing incorporating indigenous materials precedes recorded
history. Shedding of water is essential to waterproofness. Slate (ASTM C406) and other stone
materials with flat cleavage planes were used as early as the 8th century for roofing. Locally available
materials and the use of primitive felling and splitting tools led to the introduction of wood based
roofing products. Cedar provides durable shakes and shingles. Where clay is available (figure 8-1),
durable clay tile (ASTM C1167) roofing is used. Concrete and fiber reinforced concrete tiles (figure 8-
2) serve a similar purpose. Asphalt shingles and roll goods came into wide use when asphalt became
readily available as a by-product of petroleum processing. Organic shingles (ASTM D225) are a
simple, durable, inexpensive option for steep roofing. Shingles made with glass fiber reinforcing
(ASTM D3462) provide better fire ratings and require less bitumen than organic shingles. Asphalt
shingles are available in a range of qualities. It is never appropriate or cost effective to purchase low
quality shingles. Figures 8-3 and 8-4 list asphaltic roofing products used in steep roofing. Look-alike
products that use formed steel, aluminum, and plastic are other steep roof options as are architectural
metal panels. Other options for sheds where appearance is not critical include corrugated metal, roll
roofing, and the like (ASTM D224, D249 and D371).
b. General. Steep roofing systems require a roof deck (usually solid but occasionally of spaced
sheathing). Water-resistant underlayment closes in the building during construction and provides a
second line of defense against exterior moisture (e.g., driving rain and blowing snow). Asphalt
saturated roofing felt (i.e., ASTM D226 No. 15 felt) is commonly used as underlayment but pervious
plastic films and impervious peel-and-stick modified bituminous (MB) sheets (ASTM D1970) are also
installed. No. 30 asphalt saturated roofing felt is considered more durable than No. 15 and is
recommended for roofing systems with design life in excess of 20 years.
(a) The selection of steep roof systems for each climate category follows hundreds of
years of experience. Factors such as hail, intensity of rainfall, heat load, snow, and wind are important.
In addition, eave and flashing details vary to accommodate different climate demands. For example,
some old shingle roofs in the northeast U.S. use exposed metal sheets at the eaves to reduce the risk
of leaks caused by ice dams. More recently such metal has been discontinued in favor of impervious
MB sheets placed below the shingles.
(b) Where icings at eaves are of major concern, cold ventilated roofing is recommended.
The Council of Forest Industries of British Columbia recommends:
1/ Chimneys should be located at the ridge or gable ends away from possible snow
pressure on the slopes.
2/ The steeper the roof the better the performance.