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Unread 10-28-2020, 01:24 PM   #25
makethatkerdistick
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Join Date: Oct 2017
Location: North Texas
Posts: 913
Simple physics, CX. I've measured the difference myself when I had painted my shingle roof with some hydrated lime. I used an infrared thermometer. Ambient was in the high 90s on a sunny summer day (can't remember the month). The painted shingles were approx. 5-10 degs. above ambient, the unpainted gray shingles were a whopping 160 deg. F.
The metal's reflectance and albedo are similar to my experiment, just the material is more durable and also has less mass. For maximum effect, the roof has to be as white as possible. A light grey, for instance, will already get somewhat hot.

The difference is between dark and white roofs is dramatic. When the pandemic is over, I'll have to invite you to an attic tour.

Only downside is that in the winter you lose a little of that heat gain through the roof. In cold climates, white roofs are certainly a less than perfect choice.
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