Subfloor gap throws off the sheet spacing

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  #1  
Old 10-11-09, 09:05 PM
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Subfloor gap throws off the sheet spacing

I'm laying down the subfloor on my garage with tongue and groove plywood and I was going to put the 1/8" spacing between the non T&G joints, but a friend said it should be tight. Everything I've read says he's wrong, but he came up with something I couldn't dispute. The joists are on 16", and the plywood is 8ft exactly. So if I add 1/8" between each sheet, the sheet will be off the joist by the time I get to the other end of the building because of the accumulation of all the 1/8 inches.

I figured OSB wall sheeting would have the same issue, but it appears that those aren't really 4ft wide (OSB standing up), but slightly smaller. So they account for the gap between studs I guess. But these plywood sheets are really 8ft wide. So what's the deal? Do different manufacturers have different installation recommendations? If I install them tight, they all line up nicely on the 16" spaced joists. If I gap them, it doesn't work without hacking the sheets. What's the trick?
 
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Old 10-12-09, 03:28 AM
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Welcome to the forums! How many sheets are you laying down? 4 sheets is 32' and if you leave a small gap, you will only gain a maximum of 3/8" over that span. I would guess you don't have more than 24' and that would only be 1/4" over a span of 3 sheets.
 
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Old 10-12-09, 05:12 AM
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The garage is on the large side. 26ft x 56ft wide. So 7 sheets. It seems like if the manufacturer required a gap though, they'd adjust the sheet size accordingly, like the OSB size is adjusted.
 
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Old 10-12-09, 07:02 AM
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Rock2000 - on a hoot I Googled "installing plywood underlayment" The only thing consistent with the on line wisdom is the inconsistency. I found instructions that recommended spacing from 0" to 1/4".

Some spacing between the plywood sheets is recommended to minimize squeaking. The sheets are laid across the joists so the only seams that are of concern are the long side of the sheet. Spacing there doesn't effect how the sheet lands on a joist. The short side of the sheet lands on a joist and is glued and nailed. It isn't going to squeak so no spacing is needed.

I've never gapped wall sheathing. I've read that a space should be left for expansion but I can't figure out how a sheet of plywood can expand much when it's securely fastened to framing.
 
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Old 10-12-09, 04:16 PM
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My size of garage...........Nice. What Wayne said.
 
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Old 10-12-09, 05:23 PM
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When you say underlayment, you mean the subfloor or a second sheeting over the subfloor? I'm working on the initial subfloor. Maybe it won't expand enough to care about, if at all, since I'm certainly going to try to keep it dry. But I've had the OSB wall sheeting exposed a bit, and it does swell if it gets wet. In one spot that didn't have a gap the two corners kind of pushed up. If you're fast enough to avoid having stuff get wet, which you guys probably are, it might not be an issue. My speed plus the size means I'm not so lucky. Although if squeaky floors are the issue then I'm not too concerned. This is going to be a working garage, not some yuppie garage/socializing room.
 
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