Ask any roofer in Houston and they would say a cool roofing system is one that strongly reflects sunlight and also cools itself by efficiently emitting radiation to its surroundings.

The roof literally stays cooler and reduces the amount of heat conducted to the building below. If a builder 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 need not 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. Because a white roof strongly reflects both visible and near infrared sunlight, a white roof will typically be cooler than a cool colored roof.

The two basic characteristics that determine the "coolness" of an installed commercial metal roof in Houston, and other desert areas, are solar reflectance (SR) and thermal emittance (TE). Both properties are rated on a scale from 0 to 1, where 1 is the most reflective or emissive. 

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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 online Rated Products Directory. The online Directory is available to the general public at no charge, and it allows you to compare the rated values of various product types and brands.

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