This article Reprinted from Western Roofing magazine, January/February 2007, Volume 30, number 1

 

 

TPO

TPO Membranes Offer Proven Performance & Longevity

by Randy Ober, thermoplastics product manager, Carlisle Syntec Inc.

 

(Editor’s Note: Randy Ober is the thermoplastics product manager for Carlisle Syntec Incorporated. Ober’s responsibilities include marketing and product development for both the Sure-Weld TPO and Sure-Flex PVC product lines. Starting in 1983 as a research and development engineer with Carlisle’s EPDM line, he assumed responsibility for TPO product development and code testing in 1995. He currently participates in ASTM and serves as the secretary of subcommittee D08.18. Ober may be e-mailed at ober@syntec.carlisle.com.)

 

 

As a new columnist for Western Roofing, I am honored to be able to share my comments and experience regarding thermoplastic polyolefin (TPO) roofing membranes. As I have worked with TPO membranes since the early days, some may know that I am commonly referred to as “Mr. Heat Weld.” With this column, I hope to share my enthusiasm for this roofing product and offer information that will help you incorporate TPO membranes into your ongoing business. In turn, I hope the subject will generate questions that will help us all grow in our knowledge of these roofing systems

                  Although TPO has been installed on roofs throughout the United States for close to two decades, there are still questions of product longevity. We have learned over the years with EPDM membranes, which have a longer history in the commercial roofing market, which tests are most appropriate to determine long-term roof membrane performance.

                  The most widely used method to determine the resistance of TPO roofing material to UV exposure is the xenon arc weatherometer. With a 20-year technical background working with roofing membranes, I have learned that prior to releasing any new product to the field, 15-year rooftop testing is ideal. That test program should expose the roofing membrane to the actual effects of the sun in various locations throughout the country (i.e. Phoenix, for hot and dry conditions; Miami, for hot and moist conditions; Seattle, for cool and moist conditions; and Cleveland, for cold and wet conditions).

                  In the roofing industry, however, we technical types do not typically have an unlimited timetable for testing products prior to their introduction to the marketplace. This is where the xenon arc weatherometer comes in handy. The xenon arc weatherometer allows a membrane to be subjected to what is typically associated with 15 years of real time outdoor weathering in just eight months or 4,000 hours. During this exposure period, the membrane is exposed to 5040 kJ/m² total radiant exposure. (For reference, total radiant exposure is the total energy per unit area analogous to the total sunlight required to sunburn skin). This correlation is based on studies with EPDM, real life versus xenon arc weatherometer.

                  The original ASTM standard for TPO membrane (ASTM D 6878) published in 2003 specified a minimum xenon arc exposure of 5040 kJ/m² (4,000 hours @0.35W/m²) at a temperature of 80°C (176°F) without surface cracking or crazing when observed under 7X magnification. No other ASTM specification for single-ply membranes requires a higher specified xenon arc weatherometer black panel temperature. (The black panel temperature designates the temperature of a black surface inside the unit).

                  A common rule of thumb used with xenon arc testing is that the severity of the heat-aging component is doubled for each 10°C increase in the black panel temperature. Many heat-weldable roofing membranes currently specify xenon arc temperatures as low as 63°C (145°F) and some don’t specify any temperature at all. That is a key point to consider when comparing published weathering test results for any roofing membrane.

                  Early TPO formulations (1990’s) did not perform much beyond that minimum requirement due to limited technology in UV protective packages. Today, due to advances in this technology, TPO membranes easily exceed the 2003 ASTM minimum requirement for xenon arc exposure and manufacturers publish resistance as high as 17,640 kJ/m².

                  This exposure is over 12,000 hours or more than three times of that published for the earlier TPO formulations. I personally have inspected ten-year-old plus TPO roofs located in high UV areas and found good performance even on the early TPO formulations. Based on the increased resistance to xenon arc exposure, today’s advanced TPO formulations should be substantially better than those earlier products. In fact, as of 2006, ASTM D 6878 has been amended to increase the minimum xenon arc exposure to 10,080 kJ/m² or twice the original minimum.

                  Hopefully this article and future columns will not only be educational about the makeup and testing of TPO membranes but also stimulate important discussions on installation, energy efficiency, and overall performance. As seen in the recent commercial roofing study in Western Roofing magazine, TPO is showing the fastest growth in the west. It makes this column very timely. •••