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
Columbus, OH

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.

Answer

Martin Grohman

Answered by Martin Grohman

Biddeford, ME

GAF Materials Corp

April 17, 2011

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.

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