LEED Point Rating System

Landscape and Exterior Design to Reduce Heat Islands

 

Sustainable Sites Credit 7.1

 

"...use light-colored / high­albedo materials (reflectance of at least 0.3) for 30% of the site's non-roof impervious surfaces."

This requirement can be met by using concrete rather than asphalt for 30% of all sidewalks, parking lots, drives and other impervious surfaces.

Albedo, which in this context is synonymous with solar reflectance, is the ratio of the amount of solar radiation reflected from a material to the amount that shines on the material. Solar radiation includes the ultraviolet as well as the visible spectrum. Generally, light-colored surfaces have a high albedo, but this is not always the case. Surfaces with lower albedos absorb more solar radiation. The absorbed radiation is converted into heat and the surface gets hotter. Where paved surfaces are required, using materials with higher albedos will reduce the heat island effect—consequently saving energy by reducing the demand for air conditioning—and improve air quality.

Concrete generally has a reflectance of approximately 0.35, although it can vary. Measured values are reported in the range of 0.4 to 0.5. For "white" portland cement, values are reported in the range of 0.7 to 0.8. New asphalt generally has a reflectance of approximately 0.05, and asphalt five or more years old has a reflectance of approximately 0.10 to 0.15. This credit is worth 1 point.