A cool roof is one that strongly reflects sunlight (solar energy) and also cools itself by efficiently emitting any heat that was absorbed. The roof literally stays cooler and reduces the amount of heat conducted into the building below. If a building does not have air conditioning, this keeps the building cooler and a more constant temperature. If a building has air conditioning, the equipment does not have to work as hard. Imagine wearing a white or a black T-shirt on a hot day. By wearing the white T-shirt you will remain cooler than if you wore a black T-shirt because it reflects more sunlight and absorbs less heat. Cool roofs, like a white T-shirt, keep the internal temperature of the building lower.
However, a cool roof does not need to be white. There are many "cool color" products which use darker-colored pigments that are highly reflective in the near infrared (non-visible) portion of the solar spectrum.
The two basic characteristics that determine the "coolness" of a roof are solar reflectance and thermal emittance. Both properties are measured on a scale from 0 to 1, where 1 is 100% reflective or emissive.
The CRRC measures these two properties for roofing products, both for the product's initial values and after three years of outdoor exposure. The CRRC publishes the results on the Rated Roof Products Directory. The Directory enables you to compare the rated values of various product types and brands.
Visit Resources for Home and Building Owners to learn more about the benefits of cool roofs.
