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Long-Term Reflective Performance of Roof Surfaces in the Chicago Area



roof reflectance, aged reflectance, reflectance ratings, in-service roofs, roof surfaces, reflectance measurement, in-situ measurement; Chicago

The roofing industry currently relies on roof covering reflectance ratings that are based on the testing of small specimens weathered in natural environments under idealized conditions. The weathering protocols do not account for effects on roof surface reflectance from in-service influences such as roof slope, roof drainage patterns, and rooftop traffic. Also, the reflectance ratings have not been benchmarked against the reflective performance of roof surfaces aged in service. Policies with far-reaching consequences and regulations affecting the construction industry have been formulated on the basis of reflective performance ratings that may not be realized in service. We present reflectance histories of in-service roof surfaces that make possible comparisons between aged in-service reflectances of roof coverings common among commercial roof inventory in the Chicago area and reflectance ratings for equivalent materials. We carried out reflectance measurements on roof systems over a five-year period. Our observations were collected at approximately annual intervals between March 2008 and September 2012. We obtained complete five-year reflectance histories for 34 roof systems and partial histories for an additional 36 roof systems. Our findings indicate aged reflectances of in-service roof coverings typically were lower than the values available from the ENERGY STARVR Roof Products Program and Cool Roof Rating Council’s Rated Products Directory for equivalent materials. Roof systems with greater than typical slope provided examples where roof surfaces were achieving the aged reflectance ratings for equivalent materials. Our results also indicate roof surfaces may temporarily and periodically recover some reflectance losses as a result of washing by rain. Based on our findings, we offer specific recommendations for organizations administering reflectance rating programs for roof products and industry stakeholders who rely on roofing product reflectance ratings.

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