I'm going to be installing some flooring in my attic on top of the ceiling joists. This attic floor will be used to store light material like empty boxes, etc. Home Depot and Lowes have 3/8" plywood and 3/4" OSB. The price is $10.97 per sheet for either. My first thought is that the 3/4" would be better. Is there any reason why I should use the 3/8" ply instead? Thanks.
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Richard -
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Split the difference. 7/16 OSB at HD at less than $7 a sheet. I used it to deck the roof of the shed I am working on and am using it for the floor in the overhead storage areas.Don, aka Pappy,
Wise men talk because they have something to say,
Fools because they have to say something.
PlatoComment
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+1 on 7/16" OSBComment
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I'd go with the 3/4 OSB as long as you are only using it for storage. I think the 7/16th would be too thin and any narrow boxes or weight not distributed evenly across the joists might cause the OSB to sag.
If this was a floor area that saw a lot of traffic, I wouldn't use OSB at all and would go with 3/4 ply.
CWSThink it Through Before You Do!Comment
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When your roof springs a leak, the osb will go kaput in a worse way than the ply.Sometimes the old man passed out and left the am radio on so I got to hear the oldie songs and current event kind of thingsComment
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Thanks to all who replied. I didn't see anything at the local HD for $7 and didn't see 7/16 at all. The area in question will see very little traffic and anything stored there will be light in weight. As far as the roof leak, that was a concern of mine and was the reason I asked the question to begin with. (Does OSB give up when wet?) However, the house is over 40 years old and has never had a roof leak. So I guess that really isn't a great issue but bothers me anyway. Again, thanks to all who responded. I will take all opinions into consideration.RichardComment
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3/4" plywood. heat and humidity changes will affect osb far more than plywood. the alternating layers of plywood also give it more internal strength and nail holding.there's a solution to every problem.......you just have to be willing to find it.Comment
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I used 7/16 OSB in my attic in a fairly large area I use for storage. I sistered the 2x6 ceiling joists to get the "floor" up 11 inches off the ceiling so I could get adequate insulation under the "floor". The sistered ceiling joists are on 2 foot centers - as are the roof rafters. This is essentially the same construction as the roof of my house - and the same material. It sags when I walk on it but so does the roof. They do not structually fail. I have boxes of books in this storage area but I put them over the ceiling joists. My builder put up a small area this way when the house was built and I expanded it to around 500 square feet. It's been there 10 years with no issues.
7/16 OSB is sold for roof sheathing. It should rarely get wet but will occasionally. I have had water come in a poorly installed vent and the OSB is holding up fine.
I used 3/4 boards and plywood in a previous attic. It is more solid. But my experience is that 7/16 is adequate. The builder using it helped convince me.
JimComment
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I've seen a lot of OSB used of underlayment on "siding", but confess to have never seen it for roofing or flooring. But understand that I'm not in the trades or doing much in the way of outside work anymore.
But regarding the moisture concerns, I've always been under the impression that OSB was more water-resistant than normal plywood. Plywood for roofing and siding is usually marked for "exterior" use, as opposed to "interior" grade plywood. I am of the impression that OSB is the same; that is, "Exterior-grade".
Point is that I think I would make my selection of OSB or whatever based on that, and for an attic, perhaps "Exterior" grade would be the right selection. Especially if you house "hasn't had a leak in 40 years"... Unless you've recently put a new roof on it, I'd say it is overdue for a leak.
I hope this helps,
CWSThink it Through Before You Do!Comment
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I replaced an older attic storage area that had been done with OSB. Over 20 or so years the OSB had developed a significant sag and was very "spongy" to walk on. The OSB sheets had been laid so that the 8ft length of the sheet was parallel to the length of the joist and was not nailed down.
For the storage area I created I used 3/4 Tongue and Groove Plywood perpendicular to the joists screwed down every 12 inches. It's probably overkill but it sure is strudy.Comment
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