While a black roof is hot, there are a few advantages.
The heat helps to seal them quickly when they are new.
When the sun comes out, they dry quickly.
When they get old and the tar has been bleeding down the roof for many years, you can't hardly see it on a black roof.
Not every roof looks like it is bleeding tar in streaks down the roof. White seems to show them the most. I used to think that trees caused the streaks, until I put a white roof on a house with no trees around it. The streaks seem worse when the attic space is not properly vented. But even when the attic is vented very well, sometimes I still see streaks on the roof. That blue-green color would look pretty bad with a lot of streaks or other discoloration.
My theory about the streaks is this, petroleum products are continuously off-gasing. These vapors, I assume, are carrying enough black petroleum product to gather on the surface and when it rains, they are washed into a nasty pattern of streaky lines. You may have already seen what I'm talking about, if not, pay attention to some of the white roofs in your area. White isn't the only color affected, but it's the most obvious. It could be a defect in the shingles. I have seen different brands of shingles do the same thing though.
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