OSB Plywood

By
©1993-2012 Tim Carter

        
Summary: Can wet OSB plywood be used for roofing? Roofing materials, such as osb or plywood, can get wet during construction.
DEAR TIM:  My builder insists that 5/8" OSB plywood is fine for the roof. The OSB board got wet after one significant rainstorm before the shingles were able to be put on. Do you think that we will have any problems with our OSB sheathing roof? James Katzin, Emlenton, PA

DEAR JAMES: The OSB board on your roof should be just fine. This engineered-wood product is made to get wet. The lumber mills realize it's impossible for houses to be constructed in consistently dry weather.

OSB sheathing does much better getting wet than OSB subflooring. You can get swelling with OSB subflooring that puffs up the material. But roofs and sidewalls that have OSB board dry much faster than sheets that are laying horizontal on the floor.

If at all possible, allow the OSB plywood to dry thoroughly before the roofer applies the underlayment. It doesn't take long for the OSB roof sheathing to dry in most situations. A little breeze and some sun can dry the roof sheathing in hours.



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Welcome! I, Tim Carter, don't answer questions here. If you post a question here in the Comments Area, perhaps another visitor will help you. You need to go to the Ask Tim page if you want a question answered. Once there, look closely at how many weeks behind we are. Please be patient as you use this free service. If you have an emergency and need to talk to me, there is an option there for you.
Denny Mela
08 Jan 2009, 12:49
Tim:
I was also concerned when I saw OSB being used on my house when it was being built. As an experiment I put a cutoff into a 5 gal bucket of water on the jobsite to see how it would hold up. I removed it from the water about 1 month later and let it dry in the sun. It did not warp nor did it swell. I am convinced that there is more resin in the product than wood. I did notice that even without being soaked the edges of cutoffs chip off splinters very easily. It has more integrity when it is whole than after it is cut.
Bruce Atwood
20 May 2009, 17:53
I am about to purchase a house in New Hampshire that was a shell for 8-10 years. Roofing was on, and I think windows.
Is the sheathing OK? Or is it apt to be weakened by exposure to the weather?
Thanks
Amanda Holthaus-Little
29 May 2009, 07:36
My husband and I are about to buy a home and while in the attic we noticed that some of the plywood underlayment was just plain crumbling in certain areas (by the chimney and by the eaves of the house). The previous owners said they had "updated" the roof. Is it normal to lay a new roof on top of the old plywood? Is this a potential problem? Is there another layer of plywood that would have been added over the old? I know it's impossible to know without seeing, but what is the common practice?
Marcia Bender
14 Feb 2010, 19:14
During my new house construction the foil lined OSB roofing was applied. Before the paper or shingles could be installed it began to rain and did so for several weeks. Now my roof has highs at the trusses and valleys between the trusses. Could this be water damage from all the rain? Does the foil hold the water in?
Derek
16 Feb 2011, 13:09
I used OSB boards on my interior garage walls over top of the insulation and vapour barrier. Is tehre a reason why the boards would be warping? As well, i have noticed a build up of frost in some of the corners and seems, not sure if this is related or not.
Let me know what you think.
Thank you.
r dondero
11 May 2011, 16:51
hi i am installing new subfloor in my trailer over old one my question is should i waterproof it and if so what do i use thanks any help appreciated


useing o s b flooring

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