To reduce heat islands11 to minimize impacts on microclimates and human and wildlife habitats.
For each option below, if SRI information is not available for the specified product, demonstrate compliance using the SRI calculator in California’s Energy Efficiency Standards for Residential and Nonresidential Buildings (California Code of Regulations, Title 24, Part 6; available at http://www.energy.ca.gov/title24/2008standards/sri_calculator/SRI_Calcul...). This calculator uses solar reflectance and thermal emittance to determine the SRI of roofing materials.
Use roofing materials with a solar reflectance index12 (SRI) equal to or greater than the values in the table below for a minimum of 75% of the roof surface.
Roofing materials having a lower SRI value than those listed below may be used if the weighted rooftop SRI average meets the following criteria:
Install a vegetated roof that covers at least 50% of the roof area.
Install high-albedo and vegetated roof surfaces that, in combination, meet the following criteria:
12 The solar reflectance index (SRI) is a measure of the constructed surface’s ability to reflect solar heat, as shown by a small temperature rise. It is defined so that a standard black surface (reflectance 0.05, emittance 0.90) is 0 and a standard white surface (reflectance 0.80, emittance 0.90) is 100. To calculate the SRI for a given material, obtain the reflectance value and emittance value for the material. SRI is calculated according to ASTM E 1980. Reflectance is measured according to ASTM E 903, ASTM E 1918 or ASTM C 1549. Emittance is measured according to ASTM E 408 or ASTM C 1371.