[Mikendebbie]

TPO has been the "go-to" roof membrane for commercial buildings with "flat" or "low-sloped" roofs for the past 15 or so years. They lay it over Polyisocyanurate insulation (poly-iso) and it can be fully-adheared (glued which is better) or mechnanically fastened (cheaper). Typically a 60 mil thick membrane is used but they change to 40 mil sometimes to save money.

My experience is that schools do not use TPO as much, but prefer a "modified-bitumen" built-up roof - because kids get up on school roofs and mischief happens. Modified Bit is more forgiving and self-healing than a TPO membrane.

Before TPO - EPDM and PVC membranes were popular in the 80's and 90's. They are still used.

Prices for TPO and poly-iso have gone nuts in the past year. Supply chain issues cause big problems in the roofing construction process. Earlier this year - delivery for large shipments of poly-iso were 10-12 months from approval. When you need it delivered and the roofing work to start in month #5 - that is a big problem. You can't start interior finish work until the roof is on.