# drywall over OSB?



## skeeterh (Nov 20, 2010)

I'm remodeling our house and have the walls stripped to the studs.
I need to completely rewire the house but I have to do it in steps and the inspector tells me I can't close up the walls completely until the inspection has been done.
I thought about sheathing the inside of the walls with 7/16ths OSB horizontally and attaching the bottom sheet with just a couple screws to allow easy access for wiring and inspection and then drywall over that when I'm done but I've read that OSB expands and contracts quite a bit with temp and humidity changes. Would that expansion and contraction cause a problem with screws holding the drywall?
Another reason for using the osb is the old lath and plaster walls were over an inch thick so i have quite a gap at the ceiling to fill.


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## racebum (Mar 8, 2010)

not sure anyone has ever time tested this. 

quick thoughts though

if you install rock over osb in order to remove it easily you still won't be able to tape it which mean you can't really finish the wall anyway. there's really no hazard in leaving the walls open until you're done working. it also keeps it open so you aren't having to open walls twice. 

as for the actual question. solid fir which is a 2x4 will also shift, tweak and move while it dries and settles. if you've ever been in a home built in the 80s you can see what 20-30yrs of settling do on some of the walls. there's usually at least one place you'll find a couple waves. trusses and load bearing walls often show some type of deflection. anyway, if you add osb to this equation i'm not really sure it would do anything besides increase the fire potential due to more burning material being behind the rock. osb does swell when wet but if we're talking about your walls the word "wet" shouldn't be used in the same sentence as your walls. it might and i mean might increase your chance for mud cracks when you finish only because the rock will be attached to a sheet which is stretched across multiple studs, as the studs shift it pulls the sheet. then again, this may resist deflection more since osb is structurally much stronger than sheetrock. i'm not sure if anyone has tried the theory to find out.


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## skeeterh (Nov 20, 2010)

I wasn't going to put the drywall on until I was ready to finish.
It's getting a bit cold up here and thought maybe the osb might aid a bit in keeping the warm in and cold out as well as giving some semblance of real walls while the work is going on in other parts of the house. Supposed to be in the low teens this next week.


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## oh'mike (Sep 18, 2009)

Are you insulated yet? I doubt that you will have any real trouble using OSB behind the drywall--

as long as you are insulated with a vapor barrier--

I have never actually tried that ,however if the wall has a proper vapor barrier ,I would free safe myself.


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## Axecutioner-B (May 18, 2010)

I don't think there is any harm in osb behind the sheetrock, i have a framer friend who says it is a fairly normal practice to sheet a pony wall with osb ( for added strength) before putting drywall on it. Just my .02


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## Gary in WA (Mar 11, 2009)

Welcome to the forum, skeeterh! My son lives in Spokane going to Eastern. I'm near Seattle. 

Osb on the inside.... and outside already? Or diagonal boards there? 

I wouldn't do it just on the fact osb is a poor moisture transfer material. Tends to hold the moisture from showers, people, cooking, etc. and slooowly lets it go. I've heard it grows mold in attics if over the insulation on the ceiling joists there. Tends to hold water: http://www.buildingscience.com/docu...nd-the-gap-eh/?searchterm=foam board in walls

Could you use a house wrap to air seal until after electrical inspection? That would let the moisture through the wall both ways without condensing. Maybe with builder's lath attached to top and bottom plates, also an easy way to find the air leaks you need to caulk at stud/sheathing that degrades your insulation: http://www.aecb.net/PDFs/Impact_of_thermal_bypass.pdf
Pull it afterward and install it on the joist bottoms in the crawl space or attic side of the knee wall upstairs to stop from wind-washing that insulation.

Gary


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## bjbatlanta (Jul 16, 2008)

It will affect your door and window trim. You'll have to extend your jambs....


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## skeeterh (Nov 20, 2010)

GBR in WA said:


> Welcome to the forum, skeeterh! My son lives in Spokane going to Eastern. I'm near Seattle.
> 
> Osb on the inside.... and outside already? Or diagonal boards there?
> 
> ...


Thanks for the welcome.
I read your links and now my head hurts. So I need an air gap to allow any moisture to escape but air gaps drastically reduce insulation performance... 
What I've got now is a house built sometime before 1912, we found a newspaper from 1912 in a section of wall in an addition and we found .44 caliber lead balls in an older section of wall. (Sure wish they would have dropped the gun in there at the same time, that would have been a nice find) We have 2x4 studs with some sort of 5/8ths x4" siding applied horizontally. Over that we have cheap particle board siding that's pulling away from the walls and rotting in places. We planned on pulling the particle board off and sheathing with 1/2 inch foam covered in vinyl siding on the exterior and osb covered in drywall on the inside.
If osb is a problem then I guess we'll just have to live with exposed insulation for awhile longer.




bjbatlanta said:


> It will affect your door and window trim. You'll have to extend your jambs....


Not sure I understand. Old lath and plaster was over an inch thick. New wall covering would be less than an inch thick. We already installed new vinyl windows, window and door trim would need to be redone anyway.


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## bjbatlanta (Jul 16, 2008)

Sorry, I missed the plaster part.....


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