OSB roof sheathing outline

[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.

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[Jim Katen]

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

[msteger]

Is this due to a lack of H clips, thin sheathing, or settlement or something else? Looks like the shingles just magnify the issue.

[inspector57]

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.

[John Dirks Jr]

How about:

While under construction and before the roof covering went on, the sheathing got really wet and then was not allowed to completely dry before the shingles were put on. The material sopped up moisture which caused it to swell up around the edges.

[Erby]

In point of fact, it was NONE of the above except lack of proper spacing of the OSB panels and the humidity levels causing the OSB to expand.

See the Structural Board Association website on OSB:

http://www.osbguide.com/osbliterature.html

H clips are not required in all OSB applications.

[Eric B]

Erby,

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.

[carle3]

Lack of H-clips on 24 o.c. framing usaully telegraph horizontal lines at the plywood edges.