Roof reflectance, also called albedo, measures the percentage of solar radiation reflected by a roof surface back into the atmosphere, expressed as a decimal between 0 and 1. A reflectance value of 0.70 means 70 percent of solar energy is reflected, while 0.30 means only 30 percent is reflected and 70 percent is absorbed as heat.
Measurement and Standards
Reflectance is measured under standardized conditions per ASTM E903 methodology. The Solar Reflectance Index (SRI) combines reflectance and thermal emittance to provide a comprehensive rating from 0-100. Dark roofs typically have reflectance of 0.05-0.15, while white roofs achieve 0.65-0.90. Reflectance degrades over time due to dirt accumulation, dust, and weathering, declining 0.05-0.15 over 10 years.
Impact on Building Performance
Higher reflectance directly reduces roof surface temperature and cooling loads. Each 0.10 increase in reflectance can reduce annual cooling energy by approximately 2-3 percent. Reflectance also affects urban heat island effect, with wide adoption reducing ambient temperatures by 0.3-0.5°C in urban areas.