Roof Types

Steep-Slope Roofing

Steep-slope roof systems typically are composed of individual pieces or components installed in shingle fashion. Steep-slope roof assemblies typically consist of three primary parts:

  • Roof Deck — a roof deck is the structural substrate and usually is a wood-based material such as plywood or oriented strand board (OSB).
  • Underlayment — underlayment provides temporary protection until a roof covering is installed and provides a secondary weatherproofing barrier. Sometimes underlayment is referred to as “felt” or “paper.”
  • Roof Covering — the roof covering is the external watershedding material.

There are six generic classifications of steep slope roof coverings, as listed below.

Asphalt Shingles

There are three components within asphalt shingles:

  • Base material, either organic felt or glass-fiber mat, that provides support for the weather-resistant components and gives a shingle strength
  • Asphalt and fillers
  • Surfacing material, generally in the form of mineral granules, that provides protection from impact and UV degradation and improves fire resistance

The most common form of asphalt shingles are strip shingles. Shingles may be produced in a single layer or two or more layers. Many types of shingles contain a strip of factory applied adhesive that is activated by the sun’s heat after installation and seals each shingle to the next course. The seal strip also provides much of a shingle’s resistance to wind uplift.

Clay Tile

terracottabarreltileClay tile is produced by baking molded clay into tile. The density of the clay is determined by the length of time and temperature at which it is heated. Tiles may be glazed and/or surface texture treatments applied. Thus, there are a wide variety of tile profiles, styles, finishes and colors available. In addition, separate accessory tiles of various shapes designed for use on ridges, hips, hip intersections and gable ends may be available. Installation methods depend on whether the tile is two pieces, one piece, interlocking or flat.

Concrete Tile

flattileConcrete tiles are made of varying proportions of Portland cement, sand and water which is mixed and extruded on molds under high pressure. The exposed surface of a tile may be finished with cement-related material colored with synthetic 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, concrete tiles are available in a wide variety of profiles, styles, finishes and colors. Color may be added to the surface or dispersed throughout a tile. Special texture may be added in surface treatment. Each type of tile roof system may include ridge, hip, hip intersection, gable end and finial accessory tiles of various shapes.

Metal Roof Systems for Steep-Slope Applications

The three general categories of metal roof systems used for steep-slope roofing applications:

Architectural Metal Panel

Typically, architectural metal panel roof systems are designed to be used on steep slopes that will shed water rapidly over the metal panels’ surface. As a result, the seams in this system 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. The one exception is the traditional flat seamed, soldered or welded metal roof system, such as copper, which may be specified for a reduced slope. Solid roof sheathing, or decking, is required for architectural metal panel roof systems, and NRCA recommends using underlayment.

Structural Metal Panel

Structural metal panel roof systems are used on low and steep slope roofs because of their hydrostatic, or water barrier, characteristics. 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 Shingle/Single Panels

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.

Slate

slate_closeSlate is a hard, brittle metamorphic rock consisting mainly of clay minerals used extensively as dimensional stone for steep roofing and in granular form as surfacing on some other roofing materials. Roofing slate is dense, durable and essentially nonabsorbent. Slate has natural cleavage, which permits it to be easily split in one direction. Fracture, usually occurring at right angles to the cleavage, is called the grain. Roofing slate commonly is split so the length of the slate runs in the direction of the grain. Some slate splits to a smooth, practically even surface, while other yields a surface that is rough and uneven.

The color of slate is determined by its chemical and mineral compositions, which differ in various regions, thus roofing slate is available in a variety of colors. In addition, exposure to weather causes slate to change color. Slate exhibiting minimal color change is known as “permanent” or “unfading” slate. Slate that shows a stronger color change is known as “weathering” slate. Between unfading and weathering slate is “semi-weathering” slate.

Wood Shakes and Wood Shingles

woodshakesWood shakes and wood shingles are manufactured from western red cedar, cypress, pine and redwood trees. Shakes are split from logs and reshaped by manufacturers for commercial use. They are thicker at the butt end than shingles; generally one or both surfaces are split to obtain a textured effect. A split and resawn shake has a split face and sawn back. A taper sawn shake has a natural taper and is sawn on both sides. Wood shingles are sawn on both sides and have an even taper and uniform thickness. When applied to shingles, the industry terms “Perfection” and “Royal” mean 18 inch and 24 inch lengths, respectively.

Cedar shakes and cedar shingles are available pressure treated with fire retardants and chemical preservatives for increased fire resistance and to prevent premature rot and decay in some climates.

Pine shakes are made from southern yellow pine and are tapersawn. They also are available pressure treated with preservatives to protect against decay and insects. Interlayment felts are required for pine shakes.

Synthetic

“Synthetic” as it pertains to steep-slope roofing materials refers to manufactured products that replicate asphalt shingles, concrete tile, clay tile, metal panels, slate, wood shakes and wood shingles. Synthetic roof coverings contain recycled plastic and/or rubber as a key ingredient and have been available since 1993.

There are some advantages to using synthetic roof coverings when compared to their traditional counterparts. Synthetic slate, or “fake slate,” for example, weighs substantially less than natural slate allowing it to be installed over conventional roof decks. Some synthetic products purport to be hail-, mold- and algae-resistant. Lastly, several synthetic cedar shake and cedar shingle manufacturers claim a labor savings since fire-retardants or anti-algae coatings do not have to be applied to the product after installation on a roof.

Despite the benefits, there are some significant drawbacks. The relative newness of synthetic roof coverings prevents them from having a proven track record about their performance. Most synthetic products are manufactured with dyes or coloring agents. It remains to be seen if these products will fade in color due to ultra-violet exposure and weathering. It also is unknown whether these products will become more brittle or less flexible over time. And most important, model building codes do not recognize any synthetic roof coverings. You need to check with your local building department before installing these products. Because of these reasons, caution should be exercised when using synthetic roof covering products.

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