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I'm wondering if shrinkage or warping will be a concern here such that I should let it dry first. It'll be covered by 30lb roofing felt, then roll roofing, then that sealed with Henry's 884 and 887 Tropi-cool roof sealer with some sort of traction granules spread on it (at least that's the current plan).

If it's fine, should I leave the 1/8-in gap between boards like it says to do? I know some people say not to do that when attaching wet

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    I'd install it according to the manufacturer's recommendations.
    – jwh20
    Dec 12, 2022 at 11:09
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    Ice & Water Shield underlayment is superior to roofing felt.
    – Ecnerwal
    Dec 12, 2022 at 12:05

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I put down 1/2" plywood on a lean to roof addition I added to a barn some years back that was extremely wet. I thought nothing of it since it was an outbuilding, so down it went and figured it would dry in place, and so it did, with 1/4" gaps and larger occurring over time. That would not have been so bad if I had not bonded the roll roofing with asphalt, using a notched trowel. The top layer was dry enough to take the asphalt, by the time I finished installing the plywood, so that when the plywood finally dried and shrank to grow to its large gaps, it ripped the roll roofing along with it. I had many large leaks because of that.

I would not gap it at all, since it will shrink, cover it with tar paper only to protect it and let it get a chance to dry for a few weeks. Then put the roll roofing in place. THere is another "roofing underlayment" that is a woven material, that will be more durable than tar paper to handle the longer term exposure to the elements. It is more pricey, but will stay in place. The "peel and stick" type, if your plywood is really wet, may not stick to it.

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  • Thanks - I assume you were using treated / Exposure 1 plywood, right?
    – g491
    Dec 12, 2022 at 14:29
  • This was a while ago, I don't know about any particular lableing, I do know for certain it was an exterior rated sheathing typically used in home construction. Same stuff you pull off the shelves of many home improvement centers. FWIW, wood is wood, if it get wet, it swells. If it get REALLY wet, it swells up even more, regardless of the ratings stamp.
    – Jack
    Dec 12, 2022 at 14:34

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