With Roofs, Many Angles to Cover

Shape, Materials Are Interrelated

Whether a roof is flat, sloped or peaked and what weight it will bear are key in deciding on the best materials. (By Gary Walts -- Associated Press)

Winter's finally given the rooftops their first dusting of snow. But if every falling flake made you wonder whether your roof would survive another season, it's time to consider these points, brought to you with help from the Department of Energy and roofing-material manufacturers.

You need to know which kind of roof you have -- flat, sloped or peaked -- and what weight it will bear. This will determine the most appropriate roofing material. (Asphalt shingles aren't right for a flat roof, for example).

Slate of candidates: Slate is probably the longest-lasting roofing material, but it is heavy and typically the most expensive. Fake-slate roofs, made of an engineered material, are less expensive and lighter.

Asphalt shingles are the most common and economical roofing product. (Asphalt also is used in roll-roofing, built-up roofing and modified bitumen membranes.)

Single-ply Thermoset membranes, made from rubber polymers, are often called "rubber roofing"; they can withstand the potentially damaging effects of sunlight and most chemicals found on roofs.

Shingle file: New manufacturing techniques mean asphalt shingles are longer-lasting, and some companies offer lifetime warranties. There are four types of shingles: strip, laminated, interlocking, and large individual shingles.

Laminated shingles provide extra thickness. Interlocking shingles are used to provide greater wind resistance, making them most appropriate for areas near a shoreline.

Built-up roofing, used on flat or low-sloped roofs in the city, consists of multiple layers of bitumen and ply sheets. Components of a system include the roof deck, a vapor retarder, insulation, the membrane and a surfacing material -- usually a coating of hot asphalt.

More on materials: Metal roofs, common long ago, are making a comeback -- in steel, aluminum and copper, among other types. To reduce the corrosion rate, steel is galvanized with a zinc or zinc/aluminum coating. Metal is available as traditional seam-and-batten roofing, tiles, shingles and shakes. New metal roofs last two to three times longer than asphalt.

Wood shakes look different on every roof. But in addition to a distinctive appearance, they can help insulate your attic and allow your house to breathe, circulating air through small openings under the felt rows on which the wooden shingles are laid.

Traditional roofing tiles are made from clay. They are durable and low-maintenance, save energy and are environmentally friendly. Because the longevity of a tile roof also depends on the quality of the subroof, manufacturers are working to improve flashings and other aspects of the underlayment system.

Good advice: Wood shakes require regular maintenance and repair. Mold, rot and insects can be a problem. Old shakes cannot be recycled, and most are unrated by fire-safety codes. Some pressure-treated shakes are impregnated with fire retardant and meet national fire-safety standards. Others have retardants sprayed on, but the retardant needs to be renewed periodically.

What will it cost? That depends on the material selected and the labor costs for your area. Pillar to Post, a home-inspection firm, suggests a range for sloped roofs of $1.50 to $2.50 for asphalt shingles and as much as $50 a square foot for slate. Flat roofs range from $1 a square foot for 90-pound roll-roofing asphalt to $10 a square foot for single-ply membranes.

An ounce of prevention: Improper installation or faulty materials can compromise a roof. Make sure your roofer provides written proof of material and workmanship warranties.