One of the major drivers of monthly utility bills is the cost of heating and cooling your home. While insulating your attic or crawlspace can improve the efficiency of your HVAC system, there’s another step you can take to keep your home cooler during the summer months as well as reducing your overall energy usage: a cool roof. A cool roof is an addition to your overall cooling efficiency system that can save you money on your AC bill.
How a cool roof works
A cool roof is designed to reflect more sunlight from the surface of your roof than a traditional roof, making it more efficient to keep your home cool in hot weather. Similar to how wearing light-colored clothing in the sun can keep you cooler, a cool roof can reflect infrared as well as visible wavelengths of light to prevent heat from being absorbed into the roof and heating up your home. There are a variety of materials that can reflect heat from a roof, sometimes involving lighter colored materials, but also incorporating materials that reflect infrared wavelengths without changing the appearance of your roof much.
The pros of installing a cool roof
A cool roof can reduce the exterior temperature of your roof on a hot day by about 50 degrees, according to the U.S. Department of Energy. Cool roofs can cool down a home to safer levels even without air conditioning, and can give your existing air conditioner a boost, reducing your energy bill. In some cases, the exterior temperature reduction of a cool roof can extend the life of your roof by reducing wear due to heat on your roofing materials.
The cons of installing a cool roof
If you live in a cold climate, a cool roof can cause an increase to your home heating costs. In climates where what’s known as the “winter heating penalty” outstrips the energy savings of your cool roof, you should avoid installing a cool roof.
If you have an existing roof that’s in good shape, replacing it with a cool roof can be costly.
The types of cool roofs
There are a variety of materials that can be used to make a cool roof. The options available can depend on the slope of your roof, the climate you live in, and aesthetic choices.
For steep roofs (more than 2:12 pitch):
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Ceramic coated asphalt shingles
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Lighter colored wood shingles or shakes
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Composite shingles that are light in color or have IR reflective coating
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Light colored or cool coated terracotta or clay tiles
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Light colored of cool coated concrete tiles
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Light colored or cool coated metal shingles or tiles
For low-slope roofs (less than 2:12 pitch):
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Light colored or cool coated single-ply membrane
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A built-up roof with a cap sheet that has a reflective mineral coating or an added layer of reflexive marble or gray slag
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A modified bitumen sheet membrane with a mineral coating or an added reflective coating
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A spray foam roof
For steep or low-sloped roofs
A standing-seam metal roof can be used on either a steep or low-sloped roof, and can be coated similarly to metal shingles or tiles with a light color or IR (infrared) reflective finish to make it cooler.
Green roofs
Green roofs can reduce the interior temperature of your home as well, and while their installation can be complicated, a modular green roof system can save you some money on your project and provide many of the benefits of a built-in green roof.
When is the right time to install a cool roof?
Once your current roof is due for replacement, a cool roof can be installed for a similar price to a traditional roof. Replacing a perfectly good traditional roof with a cool product will be more expensive than waiting, but if you have a metal roof or a membrane roof, you can likely apply a cool coating to your existing roof, even if it’s not time for a total roof replacement.
