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.
A Global Economic Assessment of City Policies to Reduce Climate Change Impacts
Bright Is The New Black—Multi-year Performance of High-albedo Roofs in an Urban Climate
Comparing Photovoltaic and Reflective Shade Surfaces in the Urban Environment: Effects on Surface Sensible Heat Flux and Pedestrian Thermal Comfort
Cool Policies for Cool Cities: Best Practices for Mitigating Urban Heat
Islands in North American Cities
Demonstrated Energy Savings of Cool Roof Coatings and Future Directions for Research
Effect of High Aged Albedo Cool Roofs on Commercial Buildings Energy Savings in U.S.A. Climates
Energy Performance Impacts from Competing Low-slope Roofing Choices and Photovoltaic Technologies
Green and Cool Roofs to Mitigate Urban Heat Island Effects in the Chicago Metropolitan Area: Evaluation with a Regional Climate Model
Measured Energy Savings of Light-colored Roofs: Results from Three California Demonstration Sites
Measured Cooling Energy Savings from Reflective Roofing Systems in Florida: Field and Laboratory Research Results
On the Use of "Cool Roofs" to Reduce Residential Heat Exposure Disparities in Boston, MA
Soiling of Building Envelope Surfaces and Its Effect on Solar Reflectance - Part I: Analysis of Roofing Product Databases
Soiling of Building Envelope Surfaces and Its Effect on Solar Reflectance - Part II: Development of an Accelerated Aging Method for Roofing Materials
Soiling of Building Envelope Surfaces and Its Effect on Solar Reflectance - Part III: Interlaboratory Study of an Accelerated Aging Method for Roofing Materials
Special Infrared Reflective Pigments Make a Dark Roof Reflect Almost Like a White Roof
The Joint Influence of Albedo and Insulation on Roof Performance: An Observational Study
The Joint Influence of Albedo and Insulation on Roof Performance: A Modeling Study
The Potential Impact of Cool Roof Technologies Upon Heat Wave Meteorology and Human Health in Boston and Chicago
Three-Year Weathering Tests on Asphalt Shingles: Solar Reflectance
Using Remote Sensing to Quantify Albedo of Roofs in Seven California Cities, Part 2: Results and Application to Climate Modeling
The standard covers test specimen preparation and test methods for measuring the initial and aged radiative properties of roofing products. The standard is referenced by building codes and rating programs worldwide in order to measure the initial and aged solar reflectance and thermal emittance of roofing products.
California’s Building Energy Efficiency Standards for Residential and Nonresidential Buildings (Title 24, Part 6) contains requirements for the thermal emittance, three-year aged reflectance, and Solar Reflectance Index (SRI) of roofing materials used in new construction and re-roofing projects.
The L.A. Green Building Code requires roofing material used in residential buildings meet minimum values for three-year aged solar reflectance and thermal emittance, or aged SRI.