Low-slope roofs make Matt Vivona, of Father & Son Construction, Troy, Mich., shiver. “Anytime you've got low slope, or flat, you get ice and water sitting up there. It might work in California, but in a cold climate, it's a nightmare.”
In New Hampshire, Tom Avalone, whose company, Cobb Hill Construction, does both residential and commercial construction, occasionally gets requests from homeowners for low-slope roofs. In one instance, a client who'd contracted for an addition “suddenly realized that a flat or low-slope roof on the first floor would provide for a magnificent roof deck off the second story.” Avalone's recommendation? A commercial roof system, and preferably an EPDM membrane roof, at $2.50 to $3 a square foot. In this instance, the company placed a slightly pitched roof over the addition, with a rubber roof system and scuppers for drainage.
Not Pretty, but Effective Low-slope roofs go from flat to a slope of one-in-four, meaning the roof rises vertically 4 inches for each 12 inches of horizontal run. They're far more common in commercial buildings than residential. Typically, a low-slope roof is made up of continuous roofing materials such as built-up and single-ply roofing.
A problem Vivona sees is the use of steep slope materials — typically asphalt shingles — on low-slope roofs, usually by non-licensed contractors responding to the fact that “homeowners don't like to see that black rubber roof.” Vivona says he passes on the opportunity to replace shingles in such situations, because they render manufacturer warranties void and leaks inevitable.
Specialty of the House On the other hand, Rick Abril never met a low-slope roof he didn't like. Abril Roofing, in Concord, Calif., specializes in reroofing the '40s and '50s modernist Eichler houses, of which there are approximately 20,000 in the Bay area. Eichlers frequently incorporated low-slope roofs. Abril Roofing removes gravel, changes out metal drains and all edge material, then sprays on a polyurethane foam, which expands in curing to form a seamless layer. Later, a coat of acrylic is added. The foam material, a white reflective coating, insulates from the outside and keeps the roof from collecting heat. Applicators build up areas around skylights and other penetrations, to make for clear drainage and eliminate ponding, the major hazard for flat and low-slope roofs.