Over the last several years, it seemed as if TPO supporters have wanted to push the membrane onto every roof. Certainly the material has done very well and gained a large market share. But other membranes haven’t gone away, and some have a fairly stable market share. It’s easy to understand why single ply hasn’t done well on smaller roofs in urban areas, with their large numbers of penetrations and often chopped-up shapes; for these roofs, mod bit (or possibly a coating system) seems like an obvious choice.

What about PVC? It has a similar reflectivity to TPO and was the original weldable sheet. But there were questions about the plasticizers; what happens as they migrate out of the sheet? TPO was seen as being inherently flexible; over the years, it’s proven itself and has steadily improved in terms of weathering resistance. Manufacturers have been investing heavily in TPO but, surprisingly to some, pvc furniture board remains a viable alternative. In fact, we are starting to see investment in new capacity.