Tests have shown that on a 90-degree day, a white roof will only have a temperature of 110 degrees at its surface while a black roof will have a reading of 190 degrees. However, it would be a very dull country if architects and builders could not enhance the appearance of their products and were restricted to white, despite the energy savings. Consequently, roof coatings manufacturers have been developing cool roof coatings that increase heat reflectivity and reduce emissivity without sacrificing color choices.
New infrared-reflective pigments incorporated into paints used on architectural metal roofing products allow them to achieve higher reflectivity values, even in darker colors such as black and brown. This improved reflectivity — the reflectivity for black, for example, changes from 0.07 with normal pigments to 0.32 with infrared-reflective pigments — can mean a much cooler surface temperature and greater energy savings for the building below. This allows facility executives to select a sustainable roof without having to sacrifice aesthetics.
Research shows that most of the cool roof coatings and colors available today have little or no trouble meeting the reflectivity standards for the LEED and Energy Star programs. Some, however, would fall short in meeting emissivity requirements if the entire roof surface required it.
However, utilizing the weighted average calculation as defined by LEED in one of its recent Credit Interpretation Rulings (CIR), only 75 percent of the roof surface must have 0.90 emissivity; the remaining 25 percent can be anything. There are many LEED Credit Interpretations Rulings that have allowed a lower emissivity or solar reflectance — but not both — where 100 percent of the roof surface is covered by one material, including a painted metal.
This means any prepainted metal covering 100 percent of the roof, meeting the Energy Star Solar Reflectance specification, and having a thermal emittance of 0.70 or greater, meets or exceeds the LEED 7.2 credit criteria.
These Credit Interpretation Request (CIR) rulings can be critical when planning a LEED-compliant building. They are available from the U.S. Green Building Council in a catalog of questions formally asked of the Council by registered LEED projects. CIR rulings, once published, apply to all subsequent projects, and provide important guidance not found in the LEED reference manual.
WRS,LLC is a full service commercial roofing company that serves Atlanta, Athens, Milledgeville, and Augusta, Georgia. WRS, LLC also serves all of Georgia, South Carolina, and Alabama