How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manufactured and modular homes
What is a cool roof?
Tuesday, August 14, 2018
“Cool roof” is a designation for roofing material that significantly reduces the amount of heat transferred through the roof and into the home in two ways:
- Solar reflectance - Bouncing the sun’s heat back off the roof.
- Thermal emittance - The ability of the roofing material to radiate absorbed heat back into the atmosphere.
Both reflectance and emittance are rated on a scale ranging from zero to one, with one being the highest rating. The EPA’s Energy Star program, which rates cool roof materials as a basis for a rebate plan, requires that cool roof products have a reflectance of 0.65 at installation and not less than 0.50 after three years of weather exposure. Standard asphalt shingle roofs, by comparison, have a reflectivity of between 0.06 and 0.26, which results in transfer of large amounts of solar heat into the home.
Cool roof materials can be manufactured panels or flexible sheets, such as metal coated with a high-white finish or white TPO (Thermoplastic PolyOlefin -rubber-like, single-ply roofing, shown in photo at top of the page), an asphalt shingle roof with reflective granules, or a coating applied over an existing roof. The graphic below is from a catalog for Gulf Coast Supply and Manufacturing’s metal roofing color selections, with the reflectance and emittance ratings below two of their whites. You will also see a “Solar Reflectance Index,” which is a summary rating of performance.
To learn more about cool roofs, click on the link below to download a report by the Cool Roof Rating Council (CRRC).
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To learn more about roofs and attics, see these other blog posts:
Graphic - Cool Roof Rating Council
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