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What Did the Results Show?
Key Finding 1: All brands tested exceeded minimum ASTM D6878 standards
While there were variations in the three key physical characteristics (overall thickness, thickness over scrim, and weld strength) of each brand, no one brand was significantly better than any other in these tests. (See examples of results on pages 4 - 5 in SRI Executive Summary.)
Key Finding 2: There were significant differences between brands in accelerated weathering tests (D573 @ 275°F)
Accelerated weathering is one of the most important indicators of how long a TPO membrane will last.1,2
The top-performing class of membranes in the ASTM accelerated weathering test (D573 @ 275°F) were GAF EverGuard Extreme® 60 mil and GAF EverGuard Extreme® 50 mil, both of which had no visible failures for over 190 days.
The second best-performing class of membranes were GAF EverGuard® TPO and Firestone TPO, which failed at 112 days and 105 days, respectively.
The third best-performing membranes were Carlisle and Johns Manville, which failed at 77 and 70 days, respectively. (See page 9, top chart, in SRI Executive Summary.)
1Correlating Accelerated Laboratory, Field, and Thermal Aging of TPO Membranes, Journal of ASTM International, 2011, v. 8, pages 50-70.
2A Study of Longevity, Professional Roofing magazine, February, 2013, pages 44-50.
Key Finding 3: There were even more significant differences between brands in the amount of weight lost during accelerated aging tests
During the ASTM accelerated weathering test described above (D573 @ 275°F), very significant weight differences were recorded by SRI. Weight loss is important because it can lead to erosion and membrane failure. Once the membranes had experienced 1.5% weight loss, degradation occurred rapidly and the membranes were considered to have failed.
The best-performing membranes were GAF EverGuard Extreme® (60 mil) and GAF EverGuard Extreme® (50 mil), which first failed at over 190 days.
The second best-performing membranes were GAF EverGuard® TPO and Firestone TPO, which first failed at 125 days and 136 days, respectively.
The third best-performing membranes were Carlisle and Johns Manville, which first failed at 56 and 70 days, respectively. (See pages 4 - 8 in SRI Executive Summary.)
Key Finding 4: There was surprising variation in the consistency of membranes produced by each brand
It is reasonable to expect that membranes manufactured by an individual manufacturer should be relatively consistent from one production run (or from one plant) to another. However, the study found that some brands perform much more consistently than others.
The brands that showed the greatest consistency of production were GAF, Firestone, and Johns Manville. (See pages 6 - 8 in SRI Executive Summary.)