Tile Roof Systems
Clay tile is produced by baking molded clay into tile.
Concrete tiles are made of portland cement, sand and water in varying proportions. The material is mixed and extruded on molds under high pressure. The exposed surface of a tile may be finished with cementitious material colored with synthetic oxide additives. The tiles are cured to reach the required strength. They generally have lugs on their undersides for anchoring to batten strips. There are additional waterlocks or interlocking ribs on the longitudinal edges that impede movement and prevent water infiltration.
As with clay tile, there are a wide variety of profiles, styles, finishes and colors available. Color may be added to the surface of a tile or dispersed throughout (color through). Special texture may be added in surface treatment. In addition, each tile type may have separate field, ridge, hip, gable and terminal tiles that are various shapes.
Shingle Roof Systems
Asphalt shingles possess an overwhelming share of the U.S. steep-slope roofing market and can be reinforced with organic or fiberglass materials.
Although asphalt shingles reinforced with organic felts have been around much longer, fiberglass-reinforced products now dominate the market.
Organic shingles consist of a cellulose-fiber (i.e., wood) base that is saturated with asphalt and coated with colored mineral granules.
Fiberglass shingles consist of a fiberglass mat, top-and-bottom layers of asphalt, and mineral granules. Asphalt shingles’ fire resistances, like most other roofing materials, are categorized by Class A, B or C. Class A signifies the most fire-resistant; Classes B and C denote less fire resistance. Generally, most fiberglass shingles have Class A fire ratings, and most organic shingles have Class C ratings.
A shingle’s reinforcement has little effect on its appearance. Organic and fiberglass products are available in laminated (architectural) grades that offer a textured appearance. Zinc or copper-coated ceramic granules also can be applied to organic or fiberglass products to protect against algae attack, a common problem in warm, humid parts of the United States. Both types of shingles also are available in a variety of colors.
Regardless of their reinforcing type and appearance, asphalt shingles’ physical characteristics vary significantly. When installing asphalt shingles, NRCA recommends use of shingles that comply with American Society for Testing and Materials (ASTM) standards-ASTM D 225 for organic shingles and ASTM D 3462 for fiberglass shingles. These standards govern the composition and physical properties of asphalt shingles; not all asphalt shingles on the market comply with these standards. If a shingle product complies with one of these standards, it is typically noted in the manufacturer’s product literature and on the package wrapper.
Metal Roof Systems
There are three general categories of metal roof systems used for steep-slope roofing applications:
Architectural metal panel, structural metal panel and metal shingle/shingle panels. Generally, architectural metal panel roof systems are watershedding and are intended for use on steep slope roofs. Structural metal panel roof systems are used on low and steep slope roofs. Structural metal panel roof systems can be used on low slope roofs because of their hydrostatic, or water barrier, characteristics.
Because architectural metal panel roof systems typically are designed to be used on steep slopes that will shed water rapidly over the metal panels’ surface, the seams typically are not watertight. Many architectural metal roof systems are well suited for use on roof slopes of 3 inches per foot (14 degrees) or greater. One exception to the general slope guidelines for architectural metal panel roof systems is the traditional flat seamed, soldered or welded metal roof system, such as copper. It may be specified on slopes less than 3 inches per foot (14 degrees). Solid roof sheathing, or decking, is required for architectural metal panel roof systems, and NRCA recommends using underlayment.
Most structural metal panel roof systems are designed to resist the passage of water at laps and other joints, as sealant or anti capillary designs can be used in the seams. Structural metal panel roof systems possess strength characteristics that allow them to span supporting members.
Metal shingles and shingle panels are available in numerous varieties for use as steep-slope roof coverings. Most of the metal shingles are press-formed during the manufacturing process to provide a variety of shapes. These products can take the shape of individual or multiple asphalt, tile, slate or wood shingle configurations.