“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:
• Why is my roof sheathing sagging between the trusses?
• Why is granule loss a problem for an asphalt shingle roof?
• What are the mistakes to avoid when doing attic improvements?
• What causes roof shingles to curl up at corners?
• What causes shingles to buckle along a line on the roof?
• What causes leaks at a fake roof dormer?
• What causes a sagging roof ridge line?
• What causes bubble-like blisters in a built-up and gravel roof?
• Why does it cost so much more to replace a steep roof than a low slope roof?
• What is "ponding" on a flat roof?
• Is an attic required to have a light by the building code?
• How can I inspect my roof for hurricane damage?
• Why is premature curl of roof shingles a problem?
• How can I tell if a roof has more than one layer of shingles?
• What are the common problems with attic insulation?
• What is the life expectancy of an asbestos cement shingle roof?
• What's the average lifespan of a roof?
• Why is it a mistake to replace a roof and not replace its flashings?
• Why is there no attic access hatch in the house?
• What is the building code requirement for an attic access hatch, scuttle, or door?
• Does a roof with multiple layers of shingles last longer?
• What can I do to prevent roof leaks?
• Are roof trusses better than roof rafters (stick framing)?
• Why is a popped nail in a shingle roof a problem? How do I fix it?
• What are the most common problems with wood roof trusses?
• What causes a lump or dip in the roof?
• If my roof is not leaking, why does it need to be replaced?
• How can I be sure my roofing contractor got a permit?
• How many layers of roofing are allowed on a home?
• What are the dark lines running parallel to shingles on my roof?
• Can metal roofing be used on a low slope/pitch roof?
• How can I make my roof last longer?
• What are the warning signs of a dangerous attic pull-down ladder?
• How can I find out the age of a roof?
• Should I buy a house that needs a new roof?
• Should I buy a house with an old roof?
• What are those metal boxes on the roof?
• What does "lack of tab adhesion" in an asphalt shingle roof mean?
• Why do roof edges start leaking?
• Why do my dormer windows leak?
• Do home inspectors go on the roof? Do they get in the attic?
• Should I put gutters on the house?
• How much of a roof truss can I cut out to make a storage platform in the attic?
• What's the difference between an "architectural" and a regular shingle roof?
• What does a home inspector look for when examining a roof?
• Do stains on the ceiling mean the roof is leaking?
• How can I tell if the house needs a new roof?
• Why does my homeowner's insurance want a roof inspection?
• What are the hazards to avoid when going into an attic?
Visit our ROOF AND ATTIC page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.
Graphic - Cool Roof Rating Council