BY TRENT OKUMURA, ASLA, AND MICHAEL TODORAN
How to specify complex paving patterns to deflect urban heat from solar exposure.
FROM THE JUNE 2017 ISSUE OF LANDSCAPE ARCHITECTURE MAGAZINE. 
Designers are challenged by climate change as they attempt to mitigate urban heat, but among the biggest factors are the thermal properties of the very building materials they use in new developments, not least their paving surfaces. The material and color of paving make a critical difference in either contributing to or neutralizing heat gain brought by the sun (as do roofs, which typically involve simpler, monolithic material choices). Darker paving creates a hotter microclimate but lower glare, and lighter paving creates a cooler microclimate and higher glare. The sweet spot in specifying paving lies in brokering a balance between thermal and visual comfort. The crucial metric is solar reflectance (SR), which is a measurement of the relative ability of a paving material to reject solar heat. This property is determined following ASTM standards, such as ASTM C1549. The SITES rating system Credit 4.9 requires designers to use paving materials with an SR value of 0.33 at installation or a ?three-year aged SR value? of 0.28. It also requires maintenance provisions to ensure the surfaces are cleaned every two years to keep their reflectivity. Solar reflectance is one of two properties that are combined to create the Solar Reflectance Index (SRI), another commonly used metric, which assigns ...