Flat Roofing in Sterling Heights, MI

EPDM is a thermoset synthetic rubber, made to ASTM D4637 or D5019, and it comes in big sheets, so a garage or addition roof may need only one or two seams. Those seams are glued or taped, not welded. HomeGuide notes that this is where EPDM tends to break down first, sooner than on heat-welded TPO or PVC. In return, EPDM handles cold well: HomeGuide lists it and modified bitumen as the membranes that do well in cold climates. When an EPDM roof leaks, check the seam laps and curb corners before the open field of the sheet.

TPO (thermoplastic polyolefin, ASTM D6878) is laid in narrower rolls and joined with a hot-air welder, so the seam becomes one piece of plastic. Narrow rolls also mean more seams, so ask whether every weld gets checked before the crew leaves. The membrane is usually 45 or 60 mil thick. It can be ballasted, mechanically fastened with plates and screws, or fully adhered, and adhered systems cost the most. White is the common color, and it's why TPO shows up on sunny additions where a black roof would bake the room below.

Modified bitumen is asphalt reinforced with a polymer. SBS (styrene-butadiene-styrene) stays flexible at lower temperatures, so it suits cold climates, while APP is aimed at hot, sunny ones. It goes down three ways: hot-mopped, torch-applied, or as self-adhered "peel-and-stick" rolls, which keep an open flame off a wood-framed house. A typical system is a base sheet plus a granule-surfaced cap sheet. HomeGuide warns that its seams don't handle standing water well.

GAF defines ponding as water still on the roof 48 hours after the rain stops. Every low-slope membrane in the residential code, from built-up to TPO, calls for a design slope of at least 1/4 inch per foot. When the framing is dead flat or has sagged, a tapered system fixes it: polyiso boards cut with a built-in pitch, laid toward a drain, scupper or edge, with crickets between drains. Polyiso board runs $0.50 to $3.00 per square foot installed in HomeGuide's figures. A reroof with positive drainage can skip the quarter-inch rule, but on a roof that holds water, we'd pay for the taper.

Breezeways between the house and an attached garage, and the shallow roofs over a three-season room, are often too flat for shingles. Shingles need a 2:12 slope at the very least. These small roofs leak where they meet the house. The membrane has to turn up the wall behind the siding, under a counterflashing, and terminate high enough that snow piled in the corner can't reach the top. A breezeway roof usually drains to one gutter, so a clogged downspout there backs water up against the wall flashing fast. On a sunroom with skylights, each curb gets its own membrane boot.