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OSB roof sheathing outline


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Originally posted by Erby

Been looking for a long time for a picture of a roof that showed this issue clearly.

Finally found the right roof at the right time to show it.

I've seen the same issue with plywood. If we could see every roof under grazing lighting, we'd see this condition all the time.

- Jim Katen, Oregon

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Yes, it is due to all of those items mentioned plus a few not mentioned. Mainly though it is just the nature of large sheets of flexible sheathing installed in an unprotected location covered with thin material that easily transmits any irregularities and is installed in a readily observable location. If you could see similar flooring products in a similar position and lighting, chances are the same issues would be visible. Thicker sheathing, shingles, edge support, etc. will all reduce the effect.

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JLC had an article some time ago about OSB vs plywood. As I recall, OSB absorbs more moisture and is slower to release it than plywood. A roofer told me that he does not like OSB - what they were finding was that it begins to break up after all the nailing from two layers of shingles. It's one of the products that I'm waiting for people to change their minds about.

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