What is the SRI value of light gravel used on roof buildup? Where can I find a reliable SRI values database?

Question

What is the SRI value of light gravel used on roof buildup? Where can I find a reliable SRI values database?

Asked by Gunjan Shah

We are designing a building with a concrete roof in the Middle East and want to achieve an SRI of more than 78. We generally provide loose gravel on top of roof buildup.

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Answers

Martin Grohman's picture

The Cool Roof Rating Council is probably the best source.

For your application you might consider a reflective coating. GAF's Topcoat is one example. However, a ballasted roof can be surprisingly good -- here is an excerpt from the CRRC website:

  • The City of Chicago has recently updated its municipal building code to include ballasted roof systems as an accepted cool roofing alternative on low-sloped roofs as of January 1, 2010. This follows a similar decision by the California Energy Commission to recognize ballasted roof systems in its cool roofing standards.
  • The latest version of draft ASHRAE Standard 189.1 also lists ballasted roofing as a prescriptive alternative to a cool roof. A ballasted roofing system normally consists of river-rock ballast over a membrane, rigid insulation, and a metal roof deck. Though the solar reflectance is lower than a traditional cool roof, the river rock has high thermal emittance properties and the mass of the ballast acts as a heat sink, resulting in, according to some, a similar overall performance to a cool roof.