Commercial Roofing in Sterling Heights, MI

A mechanically fastened single-ply roof is held down with plates and screws driven through the membrane laps into the deck, and the next sheet is hot-air welded over the fastener row. TPO is usually 45 or 60 mil. PVC costs more, $5 to $12 per square foot in HomeGuide's figures, and lasts longer at 20 to 30 years. Both are mostly white, which reflects more sunlight than a black roof. The IBC requires a fastened or adhered roof to be designed for the building's wind uplift pressures and tested to FM 4474, UL 580 or UL 1897. Ask which assembly the fastening pattern was taken from, especially at the corners and perimeter.

EPDM can be loose-laid and held down by stone ballast, or glued to the insulation board across its whole surface. Ballast is the cheaper way to attach a membrane, and full adhesion costs the most. The building code sends ballasted single-ply systems on roofs under 2:12 to ANSI/SPRI RP-4 for design and requires the stone to meet ASTM D448 or D7655. Stone adds weight the structure has to carry, and it hides the membrane, so leaks are harder to find. An adhered roof has neither problem. InterNACHI gives EPDM 15 to 25 years.

Built-up roofing, the old tar-and-gravel roof, is three to six layers of asphalt and felt with a gravel surface. Multi-ply modified bitumen does the same job with factory-made sheets: a base ply, sometimes an interply, and a granule-surfaced cap sheet, hot-mopped, cold-adhered or torched. InterNACHI puts built-up roofs at about 30 years and modified bitumen at 20. The code wants 1/4 inch per foot of slope for both (coal-tar built-up can go to 1/8). NRCA advises against torching flashing sheets directly over combustible substrates, which is worth raising on any older building with wood nailers or a wood deck.

When a flat roof keeps failing, some owners stop replacing membranes and build a slope instead. A retrofit system sets light-gauge steel framing, typically 16 to 12 gauge, on the existing roof's structural supports, then covers it with metal panels. The old roof stays in place, so there's no tear-off and the building stays dry during the work. MBCI notes this has to go through structural engineering review, since the frame and panels add load. Slopes under 2:12 keep the cost down; steeper ones are chosen to change the building's look and for longer-term performance. Rooftop units, vents and skylights have to come up through the new plane, so plan them early.

Penetrations and drains are the places where a membrane has to be cut and sealed, so they're the first places to look for a leak. NRCA's curb details call for base flashing at least 8 inches above the finished roof. A curb that has been roofed around more than once can end up short of that, so measure it before the new insulation goes down. Where a parapet would trap water if the main drains clog, the IBC requires secondary (emergency overflow) drains or scuppers. A reroof with positive drainage doesn't have to add them, but a tear-off is the practical time to do it if the roof has ever held water. Metal edge systems on low-slope roofs have to be tested to ANSI/SPRI ES-1 for wind.