TPO and PVC are both single-ply thermoplastic membranes with heat-welded seams, and both are common on Seattle-area commercial roofs. The right choice depends on the building, not on brand familiarity.
Where They Overlap
Both systems suit flat and low-slope roofs with sound substrate, adequate drainage and manufacturer-compatible detailing. Both depend heavily on installation quality at seams, penetrations, curbs and perimeters.
Where They Differ
TPO is widely specified and cost-competitive; assembly details — thickness, reinforcement, attachment, cover board — vary meaningfully between specifications. PVC has its own material chemistry with a long track record around grease, certain chemical exposures and restaurants, and requires its own compatible accessories and repair materials.
How to Decide
Start from the roof: existing membrane identification, insulation and moisture condition, drainage, rooftop equipment and the owner’s maintenance plans. Then compare complete specified assemblies — not two membrane names on otherwise different scopes.