9/21/2009

Thinking Green: Using Light Colored Roofing and Paint

In a visit with one of my past clients today (who painted his roof white after his house closed escrow over 10 years ago), it came as a revelation that California has passed a law effective July 1, 2009, that residential roofs on new construction, both flat and sloping, must be re-roofed with a white or light material. Actually, the law for a white flat roof has been in effect since 2005. See this article provided through the California Energy Commission.

The argument is of course for energy savings, and reflects a practice long used in ancient societies that populate hot climates where light or white clothing is standard practice, and whitewash is used on all structures. The cooling effect has long term energy savings implications, especially for the Western states, and especially for California where energy conservation is fast becoming an outright demand. A California Energy Commission board member states that it has long been known that white-roofed buildings stay cooler in hotter weather:

"painting urban surfaces in warm parts of the world white or a light color could offset the carbon emissions of all 600 million of the world's cars for 18 to 20 years — at a savings equivalent to at least $1 trillion worth of CO2 reductions."

"It turns out that they cool the air outside of their walls, too. On a typical summer day, Los Angeles is 5 degrees warmer than surrounding areas, and studies have consistently shown that by far the largest factor in this discrepancy is the absorption of solar heat by dark roofs and pavement — a phenomenon known as the "urban heat island" effect."


So far, this law affects new construction, but doesn't it make sense to apply these principles to existing structures wherever possible? Rethinking guidelines for historic homes might be in order.

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