Thermoplastic Roof Membranes - Which is Which??

It is not easy to distinguish between the various types of thermoplastic roof membranes on the market today. They all look very similar. I hope that this newsletter will help when you're out on a roof trying to determine what type of roof you're looking at.

There are five basic types of thermoplastic roof membranes on the market today, listed in their rank of use as roof systems:

1. TPO (thermoplastic olefin or terpolymer olefin or tripolymer olefin)
2. PVC ( polyvinyl chloride)
3. PVC blend (Duro-Last)
4. CSPE (chlorosulfonated polyethylene, trade name DuPont Hypalon)
5. KEE (ketone ethylene ester, trade name DuPont Elvaloy)

TPO is the fastest-growing segment of the low-sloped roofing market. TPO was introduced to the roofing market in the early 1990s. The surface of a TPO membrane has a dull sheen, in contrast to the shiny surface of PVC. Welds at seams will have no material flow. TPO is usually white, although it is available in different colors.

Figure 1

PVC has been in the roofing market for over 30 years. Current manufacturers include Sarnafil and Johns-Manville. PVC roof membranes are reinforced with polyester scrim and are usually white, though they can be manufactured in any color. The surface of PVC is smooth, and in the case of Sarnafil, very slick to the touch because it has a lacquer finish. These roofs become hazardous to walk on when wet or frosty. If you look carefully at the welded seams, there will be a tiny bit of flow from the welded portion of the seam. Sarnafil imprints their name on the surface of the roof membrane.

If you are asked to look at a standing seam metal roof, but when you get there it turns out to be a single-ply roof membrane, you are probably looking at a Sarnafil Décor roof system. Décor is a metal lookalike PVC roof system.

PVC standing or batten seams are welded to a normal PVC membrane so that it looks exactly like a metal roof system from the ground. Copper patina green is a poplar color for this roof system. PVC blends include a roof system manufactured by Duro-Last. Duro-Last is usually white in color. The pattern of the polyester reinforcement is visible as raised ridges on the surface. If you look closely in the laps, "Duro-Last" or "D-L" is stamped along with the year of manufacture. The imprint is placed every 10 feet or so in the lap area and can be hard to find on older membranes. Another characteristic of Duro-Last is that the flashings are installed loosely on parapet walls and curbs. They are mechanically attached at the base of the flashings and at the top. Some Duro-Last roofs have PVC rather than metal accessories such as the edges at gutters.