It is roof vent

来源: 水鸭子 于 2007-08-01 14:46:21 [] [博客] [旧帖] [给我悄悄话] 阅读数 : (280 bytes)

To vent moistures and keep air moving in the roofs and attics.

You won't see it until you get in the attic beween ceiling and roof.

They are automatic, the hot/cold air movement keeps them moving (that's why you see most of the time, they have curves on the side).

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