CRRC product ratings are based on two radiative surface properties: solar reflectance and thermal emittance.
Solar Reflectance is the fraction of solar energy that is reflected by the roof or wall’s surface.
Thermal Emittance is a measurement of how well a material can shed the heat it absorbs. Materials with a low emissivity will tend to retain heat. Imagine a metal wrench left in the sun; it will be hot to the touch due to its low emissivity. Emissivity and color are not directly correlated.
These two properties can be used to calculate the Solar Reflectance Index (SRI) of roofing products in accordance with ASTM E1980.
The solar reflectance and thermal emittance values are used to calculate the steady-state temperature of the product in comparison to a reference black surface and reference white surface
The SRI values range from 0 to 100, though a black surface with very low reflectance and emittance could score in the negatives while a very reflective and emissive white might score over 100
It is important to note that SRI is a calculated value, not a measured value, and is a convenient way to combine solar reflectance and thermal emittance into one value
Lawrence Berkeley National Laboratory developed an Excel tool that calculates SRI
All roofs essentially fall into one of two general categories:
A highly-reflective roof can significantly reduce a building's cooling load (energy use) in many climates. However, it may also increase the building’s heating demand in winter months. This increase is usually greatly outweighed by the cooling energy savings achieved during summer months for all but the most northern climate zones in the U.S. Visit End User FAQs for more information.
In selecting a roofing product, it is important to understand your climate zone and the actual energy your home or building will save. The U.S. Department of Energy provides a free online cool roof calculator that can give an estimate of how much energy you will save. Please note that this calculator is only for low-slope (flat) roofs: DOE Cool Roof Calculator
To help determine the energy savings of a cool roof, the below documents provide an overview of some of the primary factors that influence cool-roof energy savings and identify resources available to learn more.
Cool Roof Energy Savings Brochure
Determining the Energy Savings of a Cool Roof
Cool Surface Savings Explorer is a database tool that can report the solar-reflective wall and cool roof energy, energy cost, peak power demand, and emission savings simulated for many building categories. Instructions on how to use the Explorer tool and a link to the downloadable tool can be found in the California Energy Commission report, “Solar-Reflective “Cool” Walls: Benefits, Technologies, and Implementation, Appendix P: Cool Wall Applications.”