Membrane roofing formulated from TPO (thermoplastic olefin) is tough material that’s available in white, gray, and tan, making it a popular alternative to EPDM (ethylene propylene diene monomer) rubber for rooftop decks. Unlike EPDM, in which lap joints are sealed with adhesive, seams in TPO roofing are thermally bonded with the use of a special heat gun. For a long-lasting, reliably watertight roof, keep the following guidelines in mind.

Peter Sucheski

1. Slope and Substrate The roof deck should have a slope of at least ¼ inch per foot and be free of debris or poorly driven fasteners that could back out and damage the membrane. For best results, a ½-inch-thick layer of wood-fiber recover board—the same material that’s used under rubber roofing—should be applied between the membrane and the structural deck.

2. Lapping the Membrane  Adjoining sheets of membrane should be overlapped by four inches in shingle fashion. Deck posts and other protrusions should be sealed with manufactured flashing boots of the required size and shape.

3. Sealing the Seams  A special-purpose handheld heat gun is the most practical tool for sealing seams in most residential work. Experiment on scrap to determine the best heat setting for the conditions outdoors—high for hot weather, and progressively lower for warmer weather. Completed seams should be checked with a pointed probe designed for that purpose. Any gaps should be reheated and sealed as specified by the membrane manufacturer.