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Old 05-13-12, 10:44 AM   #32
Helper EcoRenovator
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I was repainting my house bright white with sky blue trim (it was brown with a dark brown roof when I brought it) and thought why stop at the roof line, so I bought two 40lbs bags of hydrated lime (at $12 each, much cheaper than paint) and whitewashed my roof and it is now a bright white to match the walls. The advantage of whitewash is that it will gradually wear off, so by late winter the roof should be back to its original color and absorbing the winter's sun for warmth. It only took 2 hours to whitewash the roof with a paint roller, so the whitewashing process is quick and cheap enough to be an annual spring event. Also as it weathers, whitewash only releases calcium carbonate onto the surrounding landscape rather than whatever unknown chemicals are released from paint as it weathers. It should also help extend the roof life by greatly reducing the 24 hour temperature swing experienced by the shingles.

Effect: it hasn't been hot enough for A/C use since I whitewashed the roof, but on the previous day the attic vent fan (set to turn on at 120F) kicked on at 11am and shut off at 4pm, while on the two days following the whitewashing the fan never turned on. All 3 days were sunny with a high of 79F. On the original dark brown roof, I could feel the heat radiating (almost too hot to touch) off the shingles at noon, whereas the white roof just gets slightly warm to the touch.

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Last edited by basjoos; 05-13-12 at 10:48 AM..
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