A Comparison of Methods for Predicting Long-Term Performance of Commercial Roofing Membranes
The artificial weathering performance of commercial roofing membranes has been a vital characteristic to measure and evaluate in regard to predicting long-term field performance. Although single-ply membranes are the newer products in the market, they typically have more sophisticated methods for determining long-term performance than their asphalt-based counterparts. In particular, the single-ply membranes are subjected to longer term UV and thermal aging in order to predict performance, while the more established modified membranes generally use only black-oven aging to accelerate performance. This difference makes it very difficult for building owners and others to differentiate between the products. This paper attempts to compare the approaches for predicting long-term performance used in both the single-ply and modified asphalt membranes, as well as to offer some potential discussion for improving these methods in order to simplify comparisons across technologies.
In the 1990s the TPO membrane became part of the single-ply group of commercial roofing membranes, and in 2003 the American Society for Testing and Materials (ASTM, now known as ASTM International) established the first official standard specification, ASTM D6878. In this specification, weathering performance minimums were set for UV and thermal performance. This standard has been updated several times since 2003 as warranted by the advancements in polymer-aging technologies and, more importantly, as driven by field performance requirements. The ASTM was updated in 2006 to double the UV weathering standard; updated in 2008 to amend the post-UV weathering evaluation method; and finally updated twice in 2011, including an increase to the thickness-over-scrim requirements and referenced test method, as well as an increase to the thermal-performance (heat-aging) requirements.[1] The most recent discussion on the TPO ASTM standard has focused on three specific aspects of heat (thermal) aging: