TPO Roofing in the Seattle Area, WA.

TPO is a thermoplastic single-ply membrane rolled out across a low-slope deck and heat-welded at every overlap. That weld is the whole point. Instead of relying on overlapping pieces and sealant, the sheets fuse into one continuous surface, which is what lets it stand up to water sitting on it rather than running off it.

It suits this region well. The white surface reflects rather than absorbs, which slows the heat cycling that ages a membrane, and the material resists the algae and moss that colonize anything porous here. It handles ponding better than most alternatives, stays flexible through cold, and is straightforward to repair years later because new material welds to old.

What it is unforgiving about is workmanship. A weld made at the wrong temperature looks identical to a good one on the day and separates two winters later. Penetrations, parapets, curbs and drains need proper detailing rather than a bead of sealant. And TPO over a roof that ponds because the slope was never corrected will fail at the seams regardless of how well it was welded. We correct the drainage first.