Metal Cool Roofing with Infrared-Reflective Paint Pigments

New infrared-reflective pigments are being incorporated into paints used on architectural metal roofing products to allow them to achieve higher reflectivity values, even in darker colors such as black and brown. This improved reflectivity (e.g., black changes from 0.07 with normal pigments to 0.32 with infrared-reflective pigments) can mean a much cooler surface temperature and thus greater energy savings for the building below, and allows facility executives to select a sustainable roof without having to sacrifice color choices and aesthetics.

To get the one point for Sustainable Sites Credit 7.2: Heat Island Effect, the U.S. Green Building Council’s Leadership in Energy and Environmental Design (LEED) green building rating system specifies Energy Star requirements, adding a 0.9 emissivity standard. For steep-sloped roofs, those with a rise-to-run ratio of 3:12 or greater, a 0.25 initial solar reflectance is required. In most cases, coated metal roofs can easily surpass the reflectivity requirement, and in some cases, they can achieve the 0.9 emissivity. But more often, they can only achieve an emissivity of 0.85, thereby eliminating them from achieving the LEED point.

For low-sloped roofs, those below 3:12, and flat roofs, the LEED reflectivity requirement is raised to 0.65, and the 0.9 emissivity standard is the same.

The Cool Metal Roofing Coalition, an organization comprised of metal industry trade associations, is providing written commentary and data to USGBC requesting consideration for a reduction of the emissivity standard to around 0.7. The Coalition contends that in addition to metal roofing’s energy efficiency when the reflective pigments are incorporated into a system’s design, metal’s long term ability to retain its reflective properties and a low life-cycle cost justify reducing the standard. The 0.9 standard “restricts a building owner’s ability to apply a suitable, long-term roof,” says Greg Crawford, executive director of the Coalition. The emissivity standard of 0.9 “is somewhat arbitrary,” says Andre Desjarlais, program manager for the Building Envelope research program at Oak Ridge National Laboratory, a supporting member of the Coalition. The 0.9 standard “is not defensible, but neither is eliminating emissivity altogether. We’re searching for middle ground.”

Please also see the March 2004 facilitiesnet.com article by Greg Zimmerman titled "Do Cool Roofs Fit In Cool Climates?"



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