On a sunny summer day, a typical roof surface can reach temperatures that are nearly 100°F above the ambient temperature. A cool roof, by contrast, stays at or near the ambient temperature due to the characteristics of its outer layer. There are many benefits to keeping a roof ’s surface cooler, including air-conditioning energy and demand savings, monetary savings, increased human comfort both indoors and outdoors, and other positive impacts on urban environmental quality.

Although the actual benefits of a cool roof on a particular building will depend on many factors, including building type, load, season, and climate zone, cool roofs can significantly reduce summer electrical energy usage. In low-rise buildings, a typical application will achieve air-conditioning energy savings of approximately 10% to 20%. The energy savings achieved through cool roofing translate into monetary gains for building and facility owners, as well as help reduce emissions of atmospheric pollutants and greenhouse gases.

Under the 2005 California Title 24 standards, cool roofs are assumed as a baseline in the model buildings that establish the required energy performance for nonresidential buildings with low-slope roofs. However, installing cool roofs is not mandatory for new construction. Although not mandatory, cool roofing is often the least expensive option to achieve the required energy performance; consequently, cool roof technology is gaining more attention in the building industry. Owners, designers, contractors, and other stakeholders need to have a better understanding of how a cool roof can be successfully applied to new construction projects and re-roofing projects.

This design brief provides information about how a cool roof works. Focusing on commercial and industrial low-slope roof applications, the benefits of implementing a cool roof are also described. Design considerations are discussed, and the methods of applying cool roof technology to comply with California Title 24 building requirements are described. Finally, several examples of cool roof applications are provided.