I'm putting up a large GRP flat roof. The builder has been AWOL for a while, and so the roof has been left with just OSB3 with no waterproof covering. It's been rained on for months and swelled to twice its original thickness.

Is this board still OK to use for the roof if I can let it dry? I can still walk on it with no problems.

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    Hello, and welcome to Home Improvement. I'm no pro, but my guess is "hell, no." And, please take our tour so you'll know how better to contribute here. – Daniel Griscom Jun 13 at 12:15
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    Usually OSB3 board has a water exposure rating and it's designed for what the manufacturer considers "normal" exposure during construction. It sounds, however, like your situation is far beyond normal. I'd check with the manufacturer or the dealer of the product in your area for an assessment of how much water has been absorbed and if it's still safe to use. My guess, however, is that this is going to be a total replacement job due to negligence on the part of the builder. – jwh20 Jun 13 at 12:18
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    diy.stackexchange.com/questions/32820/… Closely related – Kris Jun 13 at 12:47
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    Possible duplicate of Is it OK for OSB3 boards to get wet during construction? – tk421 Jun 13 at 14:17
  • If it has swelled that much the bond of the strands has surely been compromised. I can almost guarantee that no manufacturer will support using it, and then you're left with a subjective risk tolerance issue. Voting to close as a duplicate, but also as opinion-based. – isherwood Jun 13 at 18:22

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