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Old 10-17-2012, 11:19 AM   #1
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Spacing between plywood?


I just had a hip roof constructed on a small detached workshop. The rafters are 16" OC and the deck is 15/32" 5 ply CDX, 4:12 pitch. I'm very happy with the roof, which has not yet been shingled. I noticed that a lot of the plywood sheets butt tight together, while others have a small gap of about 1/8".

I've read that there should be spacing between the sheets of ply. Can someone tell me if I need to kerf the roof decking to achieve the spacing? I intend to use #15 felt with asphalt shingles. This is in California, very mild climate.

Thanks.

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Old 10-17-2012, 01:18 PM   #2
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Spacing between plywood?


typically the sheets should have 1/8" gap between them (width of shaft of 8d common nail) for expansion. measure the sheet that is butted tight and see if it is 96" x 48". if it's over that means it has absorbed some moisture and expanded already.

I'm sure you'll get better answers from the roofing experts.

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Old 10-17-2012, 02:31 PM   #3
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Spacing between plywood?


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Originally Posted by GBrackins View Post
typically the sheets should have 1/8" gap between them (width of shaft of 8d common nail) for expansion. measure the sheet that is butted tight and see if it is 96" x 48". if it's over that means it has absorbed some moisture and expanded already.

I'm sure you'll get better answers from the roofing experts.
The plywood was installed 13 days ago and today I measured the 48" width. It looks like it is 1/32" wider. The 96" length was cut down, so I have no real reference point on the long side.

Should I expect further expansion? If this is about the max expansion, then I won't worry about it.
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Old 10-18-2012, 12:05 AM   #4
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Spacing between plywood?


CDX plywood is "sized for spacing", read the ink stamp on the underside: http://www.apawood.org/pablog/index....f-plywood#more You could get more swelling- possibly. Especially with a roof leak though in a shed you would see that. The long-edge gap is important or it could buckle. Both are... even dangerous if not in OSB, fig. 14: http://www.buildingscience.com/docum...on?full_view=1

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Old 10-18-2012, 11:37 AM   #5
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Spacing between plywood?


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Originally Posted by GBR in WA View Post
CDX plywood is "sized for spacing", read the ink stamp on the underside: http://www.apawood.org/pablog/index....f-plywood#more You could get more swelling- possibly. Especially with a roof leak though in a shed you would see that. The long-edge gap is important or it could buckle. Both are... even dangerous if not in OSB, fig. 14: http://www.buildingscience.com/docum...on?full_view=1

Gary

I checked my plywood and it does not have "sized for spacing" on the label. Also, I'll be hanging drywall on the joists, so the only way I'll notice a leak is when the it appears on the drywall.

This is a 11' x 15' workshop with 4:12 hip, so not a lot of work to kerf some spaces. I think I'll do that and then not worry about.
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