01 May 1999
3/ Plumbing pipes should be located on inside walls and should be extended
between the rafters and vented at the ridge.
4/ Wide overhangs at the eaves should be avoided as they provide large cold areas
for snow and ice buildup.
5/ A strip of metal along the eaves helps shed ice.
6/ Sliding ice and snow are constant hazards and should be given primary
consideration in the total building design. Outside doors should not be located at the bottom of a roof
slope. Entrances and all pedestrian traffic areas are better situated beneath the gable ends of the roof.
7/ In regions of heavy snowfall, wood shingles and shakes should be installed as a
three-layer roof. For shake roofs, two layers of shingles and one of shakes are recommended at the
8/ Sidelap of wood shingles should be increased to 51 mm (2 in.) instead of 38 mm
9/ A typical cold roof detail is shown in Figure 8-5.
(2) Logistics. Long ago steep roofs used only local materials. This has changed with the
introduction of lighter materials and greater transportation efficiency. However, freight can be a major
cost factor with heavier and bulkier products. Loading of a roof and scaffolding for extreme slopes is a
(3) Familiarity with the System and Site. Some steep roofing materials (e.g., shingles) are
common and well known. Installers need to be experienced in their installation. Valleys, penetrations,
and flashings require the most skill. Information on steep roofing systems is readily available from
manufacturers and trade associations; especially useful is the Steep Roofing Manual from the NRCA.
(4) Product Comparisons. Figure 8-6 compares costs, longevity, and pros and cons of
common watershedding roofing systems. Scaffolding for complex and extreme slopes will greatly
8-2. BUILDING ELEMENTS.
a. Slope. In wet, cold, or windy climates minimum slopes should be increased.
b. Low-Sloped Roofs.
In some cases, lower slopes are permissible when waterproof
underlayments are used. These may be self-adhering modified bituminous sheets or overlapping of a
field sealed bituminous sheet. Bituminous built-up membranes with mineral surfaced cap sheets are
used as underlayment for mortar-set tile roofs.
c. Steep Roofs. At extreme slopes (> 21:12) (e.g., mansard constructions) manual tabbing of
asphalt shingles is needed.
d. Structural Considerations. Tile and slate systems are heavy. Lightweight tile systems may be
suitable in regions of infrequent freeze-thaw cycling.
(1) Weight of Common Slate and Tile Roofings.