The amount of sunlight that hits the walls of a building differs from that of a roof over the course of the day and year, with less solar energy hitting the wall overall. However, walls also generally have less insulation than roofs, with about half the amount of resistance to heat flow than that of a roof. These two factors combined result in similar savings from cool exterior walls to that of cool roofs.
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.