Over the course of six months, Weathercraft identified two failed TPO roof membranes in Colorado Springs. Both systems exhibited the exact same mode of failure; and we suspect they were manufactured by the same membrane manufacturer. After consulting with several leading roof membrane manufacturers and the National Roofing Contractors’ Association (NRCA), it appears that some TPO manufacturer’s will need to revise their formulation.
Two possible reasons for the failures 1) The membrane must be able to withstand more heat than originally anticipated and 2) the membrane needs an adequate thickness of TPO over the reinforcement.
We have already seen manufacturers offer “new” “extreme” weathering packages to handle higher temperatures. Because the TPO membrane is white (in most cases), the membrane was expected to reflect much of the heat and remain cooler. What has been determined is that roofs do not stand alone. Building components, methods, and materials can subject the membrane to much higher temperatures than originally believed.
It has always been our philosophy to avoid the minimal thickness sheets. Specifically with the reinforced TPO membrane; the membrane lacks the waterproofing or thermoplastic material on the weathering side of the reinforcement. We recommend single ply membranes of 60 mil thickness or greater. The thicker sheets have more of the waterproofing material over the reinforcement.
It is suspected that American Society for Testing and Materials (ASTM) will revise ASTM D6878 to dictate the amount of TPO waterproofing that is on the exposed side of the sheets reinforcement.
As with any new product, there are lessons learned. TPO membranes are not the exception. Choose a good manufacturer, don’t skimp on the thickness and use a reputable, commercial, roofing contractor. Your roof will have a better chance of lasting the test of time.
John Fleming