Cool roofs are defined by the Cool Roof Rating Council as a product with solar reflectivity of at least 0.70 and infrared emissivity
of at least 0.75. In its 2005 revision, Title 24, California Energy Efficiency Standards for Residential and Nonresidential
Buildings, cool roofs are prescribed in the standard non-residential building. While cool roofs decrease the solar gain of buildings, thus lowering cooling energy demand, additional insulation also does it. This work investigates the levels of insulation required with a black roof to accomplish the same cooling energy demand that cool roofs have with minimum insulation requirements.
Both total and peak energy demands are considered and the levels of insulation to accomplish them are different. Oak Ridge
National Laboratory’s Simplified Transient Analysis of Roofs (STAR) computer code was used to predict the transient heat gain and structure temperatures. The 16 Climate Zones in California were used, as well as the minimum insulation requirements dictated by 2005 Title 24 legislation. The results were compared with the results predicted by the overall envelope approach of the legislation.
Bianchi, M., Miller, W. A., Desjarlais, A. and Petrie, T., “Cool Roofs and Thermal Insulation: Energy Savings and Peak Demand Reduction.” in Thermal Performance of the Exterior Envelopes of Buildings X, proceedings of ASHRAE THERM X, Clearwater, FL, Dec. 2007.
Produced for ASHRAE Therm X
Publication Date: December 2007