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Roof Decking Too Thin???


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Don't know what code you were under there 24 years ago, but today 5/16" plywood is permitted on 16 inch centers and 3/8" is permitted on 24 inch centers (IRC 602.10.3 or UBC 2320.11.2-3.) It has to be rated for that type of exposure or it's a no-go. In other words, APA Rated Sheathing Exp 1, APA Rated Sheating Ext, APA Rated Sheathing/Ceiling Deck Exp 1, APA Structural 1 Rated Sheating EXP 1, or APA Structural 1 Rated Sheathing Ext.

However, since you didn't say, I'm assuming it's an asphalt composition roof, in which case it has an expected maximum service life of only about 20 years anyway. Based on what I see there and the fact that it's a 24-year old house, I would have simply stated that the roof deck is rotting and the roof, including the sheathing, is at end of service life and must be torn off and replaced. I'd probably also add something like, "replace any rotting rafters" as well.

Deferring it to a roofing contractor for full evaluation leaves it open to interpretation. If the homeowner hires the right person, a finding of, "There's nothing wrong here that a few new shingles where it's leaking won't fix," is what the finding will be. Then they'll convince your client that everything will be hunky-dory after a few new shingles, and in the not-too-far-distant future you'll be asked to shell out the cost of a new roof, because your recommendation wasn't strong enough.

Though we are supposed to be objective, we are also hired to be our client's advocate. Don't be wishy washy about this kind of stuff or it's gonna bite you hard one day.



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Ain't it a shame what "code minimum" allows?

I point out 3/8" decking as "minimal" or "marginal", along with expression of regret about cheap construction.

I've written several roof replacement jobs for housing rehab, and every time the contractor tries to remove old shingles from 3/8" decking, the stuff delaminates and huge pieces come away with the shingles.

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As an ex APA Field Rep (1968 to 1974)I know APA - The Engineered Wood Association has done extensive testing of plywood roof decking and 5/16" on 16" centers it is plenty strong structurally. It does give under foot and that is one of the reasons for ply-clips between supports. The ply-clips keep the panel edges moving together to help keep from tearing shingles. The one weakness I see to 5/16" decking is the holding power of shingle nails. 3/8" decking is better.

I don't see any 5/16" decking here, but I do see a lot of 3/8" decking on 24" centers in Central Texas. Occasionally a client will complain about give or a spongy feeling when he walks the roof, but I have never seen a performance failure.

I left APA before they got into OSB. I my APA days we used to badmouth OSB type products, but that was before APA members started making it. Now they promote it.

APA is a reliable, reputable group and you can take their recommendations to the bank.

My opinion. Worth what you paid for it.

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