Steep-Slope Roof Coverings
The following roof coverings are commonly used on steep-slope roofs. These coverings are water shedding, rather than waterproofing. Special underpayment provisions are required when slopes are relatively low. The NRCA Roofing Manual provides underpayment guidance.
METAL PANELS AND SHINGLES
When used on slopes greater than 3:12 (25 percent), hydro kinetic or water-shedding panel systems may be used. Hydro static (water barrier) systems may also be used. Structural panels may be specified if a solid deck is provided. If a solid deck is not provided, structural panels need to be specified.
Metal shingles are also available in a variety of metals and designs. The performance varies greatly depending upon the product selected.
Shingles are available with either fiberglass or organic reinforcement. Fiberglass-reinforced shingles provide greater fire resistance and are therefore recommended. Asphalt shingle products are typically tested and classified for impact resistance according to UL 2218. This standard provides for four classifications: Class 1, Class 2, class 3 or Class 4. Class 1 provides for the least measured resistance of impact resistance, and Class 4 provides for the relatively greatest level of impact resistance. NRCA suggests designers consider specifying asphalt shingles with Class 3 or Class 4 in regions prone to large-sized hail.
In addition to the traditional three-tab design, laminated (structural) shingles are available where a different appearance is desired. Product standard ASTM D3462 has limited criteria to distinguish various products in the marketplace. Therefore, warranty duration is normally used to attempt to distinguish commodity products from those that offer longer service life. However, the warranty duration is not necessarily an indication of performance. Shingles with a minimum warranty of 25 years are recommended.
Natural slates have the potential to offer several decades of service life. However, slate is heavy and very expensive. If slate is specified, a very durable underlayment is recommended, so that it does not prematurely degrade.
Specifiers are cautioned that synthetic materials are often marketed as slate. Some of these products are made from slate particles, while others are made from polymers or other materials. Synthetics should not be expected to offer a service life equivalent to natural slate.
Tiles can either be made from clay or concrete. Tiles typically can be expected to offer a longer service life than asphalt shingles. However, tiles are heavy and more costly than shingles