Aged Solar Reflectance

The aged solar reflectance values are shown in Figure 19. With the exception of locations 17 and 18, the roofs showed an average value of 0.665. This is only slightly below the 3-year aged solar reflectance of 0.68 reported by the Cool Roof Rating Council (CRRC) for this membrane.¹⁶

Figure 19. Solar reflectance values of the aged cool roof membranes.

The 0.44 and 0.38 values exhibited by Locations 17 and 18, respectively, suggests that the area sampled was particularly contaminated—a condition that could possibly be resolved by cleaning. Many roofs have localized contaminated areas, such as those that occur near drains or low points. Taken overall, the results suggest that the published three-year solar reflectance values generally can be used to model long-term energy efficiency of these roof systems.

Interim Conclusions

While more evaluations are underway, the data collected to date on the 20 aged TPO roofs evaluated suggests that the membranes are performing well. There were no geographical differences noted and the results indicated that the roofs are capable of achieving their expected service lives. The authors will continue to analyze data and look for trends between climate zones, exposure, membrane thickness, application method, and more as data becomes available.

The ply adhesion values of new repair membrane to the aged TPO membrane are primarily above the average ply adhesion values anticipated for new TPO membranes. This provides validity to the integrity of repairs to aged TPO membranes and the ongoing maintainability of these roofs.

In a few instances, the film-tearing bond was below expectations. The data suggest that there were issues with the workmanship in these few cases, which points to the importance of weld quality checks throughout a roof installation. These would involve test welds to determine the percent film-tearing bond.

The TOS values for all roofs tested suggest that there is little to no erosion of these membranes. Also, no instances of surface cracking when bent over a mandrel were observed. Taken together, these two observations suggest that the membranes are aging very well and in line with the requirements outlined in ASTM D6878.

Solar reflectance data were largely in line with published three-year aged values from the CRRC. This suggests that the generally held assumption that the three-year data are indicative of long-term solar reflectance is correct. Therefore, where that value is used to model building energy efficiency and/or specify HVAC equipment sizes as a result of membrane choice, the membrane is performing to long-term expectations.

The findings to date illustrate the robust performance of TPO membranes as they age. Given the inherent flexibility and fungal resistance of TPO, and the UV and heat stabilizers, this comes as no surprise. However, the ability to repair aged TPO membranes has been undefined and anecdotal to date. The interim findings of this study clearly demonstrate the weld integrity of properly executed repairs to aged TPO membranes.

In summary, the aged TPO membrane roofs in this study are performing well and in most instances, meeting the current ASTM D6878-19 requirements for newly manufactured membranes.

• Even after 12 or more years of aging, both the 45- and 60-mil membrane samples exceeded current thickness requirements for newly manufactured TPO membranes.
• Both the 45- and 60-mil membranes analyzed in this study are still in compliance with these newly manufactured membrane requirements, with the thickness over scrim averaging over 40 percent of the actual aged membrane thickness.
• All of the samples, both the 45- and 60-mil membranes, exhibited no signs of cracking when bent over the mandrel and viewed at 7X magnification.
• All of the 60-mil samples tested to date still meet cold temperature flexibility requirements after 12 or more years of aging. The 45-mil samples showed signs of cracking at -35F. While this is still good performance and aged membranes cannot be expected to perform at the same level as new membranes, the data supports the use of thicker membranes for longer performance.
• Ply adhesion values of the aged TPO membrane were 15-percent above the average ply adhesion value from the SRI study on new TPO membranes. As expected, the aged welds appear to be performing well and are of adequate strength.
• Ply adhesion values of new repair membrane to the aged TPO membrane are above the average ply adhesion value for new TPO membranes. This provides some validity to the integrity of properly executed repairs to aged TPO membranes.

Resources

gaf.com/tpostudy

¹ Demonstration/test roof, material supplied by Montell Corporation (later incorporated into Basell Corporation, which subsequently became Lyondell-Basell).

² H. R. Beer, “Longevity and Ecology of Polyolefin Roofing Membranes,” Proceedings of the Fourth International Symposium on Roofing Technology, Gaithersburg, MD, Sept. 17-19, 1997.

³ H. Hardy Pierce, C. McGroarty, and T. J. Taylor, “An Unprecedented Study Shows Surprising Differences Among TPO Membranes,” Professional Roofing, Aug. 2015, pp. 38-42.

⁴ ASTM D08.18.05.08 Meeting, Atlanta, December 7 – 9, 2009.

⁵ T&R Committee Advisory on TPO, Midwest Roofing Contractors Association, Inc., February 10, 2010.

⁶ T. J. Taylor and L. Xing, “TPO Membranes, UV and Heat Aging. What are the latest findings?,” MRCA 61st Annual National Conference, Indianapolis, October 28 - 29, 2010.

⁷ Midwest Roofer, Midwest Roofing Contractor Association, January/February 2011, pp. 8-9.

⁸ C McGroarty and T. J. Taylor, “A Study of Longevity – Long-Term Performance of TPO Roof Membranes Can Vary,” Professional Roofing, February 2014, 44 – 50.

⁹ T. J. Taylor and L. Xing, “Accelerated Aging of TPO Membranes—Prediction of Actual Performance,” Roofing Research and Standards Development, Vol. 8, ASTM Int., 2015, pp. 139-152.

¹⁰ S. Croce and M. Fiori, Polyolefin Roof Membranes On Site Durability Evaluation, 11th International Conference on Durability of Building Materials and Components, Istanbul, Turkey, May 11-14th, 2008.

¹¹ C. Chapman, K. C. Barnhardt, C. Madsen, J. Carlson, A. H. Delgado, R. M. Paroli, R. Ober, D. Wacenske, M. Ludwig, D. Hunt, W. Collins, and S. Elliot, “TPO Roof Research and Testing Project,” 10th-Year Update Report, Western States Roofing Contractors Association, Western Roofing, July, 2011, pp. 1-18.

¹² Hans-Rudolf Beer, et al. Long-term Field Studies and Residual Service Life Prediction of FPO Roofing Membranes, DBMC XII, April 2011.

¹³ F. J. Foley, J. D. Koontz, and J. K. Valaitis, “Aging and Hail Research of PVC Membranes,” 12th International Roofing and Waterproofing Conference, Orlando, Fla., Sept. 25-27, 2002, pp. 1-25.

¹⁴ Dupuis, Rene M., “Final Report on 2013-2014 Broad Sampling TPO Test Program,” 2015 pages 1-7.

¹⁵ Simmons, T. R., Runyan, D., Liu, K. K. Y., Paroli, R. M., Delgado, A. H., and Irwin, J. D., “Effects of Welding Parameters on Seam Strength of Thermoplastic Polyolefin Roofing Membranes,” Proceedings of the North American Conference on Roofing Technology, 1999, pages. 56–65.

¹⁶ Cool Roof Rating Council, coolroofs.org/products/results

Jennifer Keegan, AAIA, has over 20 years of experience as a building enclosure consultant and provides technical leadership within the industry through IIBEC, ASTM, NWIR, and Women in Construction. www.linkedin.com/in/jenniferkeegan