Keeping It Light: The Scoop On Cool Roofs

by Grace Motley

What exactly is a "cool" roof? The roofing industry uses that term to refer to any professional roofing systems that help save energy costs for heating and cooling the building beneath them. The appeal is clear: Lower energy bills and a way to help the environment.

But not all commercial building owners or homeowners will find that a cool roof saves money. A lot depends on the climate where the building is located, the type of roof and the building's position. Of course, the final authority on whether a cool roof is a good investment should be your experienced roofing contractor.

How is the "cool" factor of a roof rated?

There are two measurements or factors that determine how cool a roof is. According to the Cool Roof Rating Council (CRRC), these should be measured initially and after three years of exposure to see how well the roof does:

  • Solar reflectance (SR). This is the amount of the sun's energy that is reflected out by the roof.
  • Thermal emittance (TE). This is how well the roof's surface radiates or distributes out the heat it has absorbed.

What are the key pieces to a cool roof?

  • The color. A light colored roof automatically will reflect more heat and keep a building cooler in warm months than a darker roof. While most residential roofing materials don't come in white, there are many lighter colored options and new products coming on the market that are designed to reflect light and heat. Commercial buildings may have more options for light colored materials.
  • Radiant barrier. A barrier under the rafters that is designed to repel heat will also keep the roof and immediate space underneath (like the attic) cooler.
  • Proper roof venting. Intake vents installed correctly and exhaust vents positioned high on the roof are important to maximizing proper air flow, which keeps the building cooler. Improperly installed vents can actually create a warmer attic space that lets too much moist air into the building.

Do cool roofs really save energy?

When installed correctly with the right materials for your climate, a cool roof can save between 7 and 15 percent of your annual cooling costs.

If you don't have air conditioning, a cool roof can keep you from needing it in all but the warmest climates. And if you do have an air conditioning system installed, you will use it less and more efficiently, meaning it will last longer and cost less to operate.

If saving money on cooling costs and helping improve the environment sound good to you, talk to your professional roofer about whether a cool roof is the right solution.