01
Know the three terms
Solar reflectance describes the fraction of sunlight reflected by a surface. Thermal emittance describes how effectively the surface releases absorbed heat as thermal radiation. Solar Reflectance Index, or SRI, combines those properties in a calculated comparison. An SRI number is not a percentage reduction in a building’s energy bill.
02
Ask about the exact product
Request documentation for the offered material and finish, including any initial and aged values relevant to the project. Visual color alone is not a substitute for measured data. Confirm that a rating belongs to the product being purchased and that any directory listing can be located by the design team.
03
Separate product data from compliance
Have the designer identify the requirements that apply to the project location and scope, then compare the documentation with those requirements. A general statement that slate is natural or durable does not answer a cool-roof question. Do not assume that another project’s acceptance establishes acceptance for yours.
04
Consider the complete building
Roof surface properties are one part of an energy discussion that also includes insulation, air leakage, roof geometry and local climate. Ask for the project’s design reasoning rather than a universal savings figure. Keep energy claims distinct from appearance, lifespan and repairability when comparing roof options.