OSB as a base layer under drywall - off gassing?

[colliderman]

Hey all,

I'm trying to decide if I should use OSB as my first layer on my interior walls before putting a layer of 5/8" drywall.

I've seen that this is quite common in studio builds because it provides a substrate to screw into when placing treatment on the walls. I'm also planning to build ceiling to wall soffits for my ducting as well as lighting, so having OSB there for the soffit framing would make things much easier.

My concern though is off-gassing from the OSB. I once put up a layer of 1/4" OSB covering a bedroom wall that was then to be covered with barn-board. Well, after getting the OSB up and giving it a few days I had to remove all of it because the smell was terrible. There's no way that I would have felt comfortable sleeping in that bedroom knowing the OSB was emitting noxious chemicals.

So this makes me naturally second guess putting it up as a first layer in the studio. Of course, in the studio, the OSB will get covered up air-tight with 5/8" drywall, so maybe it's nothing to be concerned about?

The other option is using plywood but it's twice the price and less dense so the isolation would suffer.

So just curious if anyone has had this concern or dealt with this and how they decided to proceed? Will the drywall layer take care of any potential fumes from the off-gassing in the living space?

[eightamrock]

I used plywood in my build for the reasons you mentioned and also more mass. I have 1 plywood, 2 5/8" layers with green glue on all layers.

I recommend plywood over OSB because it holds screws better and its a bit denser.

[colliderman]

Source of the post I used plywood in my build for the reasons you mentioned and also more mass. I have 1 plywood, 2 5/8" layers with green glue on all layers.

I recommend plywood over OSB because it holds screws better and its a bit denser.

Thanks for your input!

Ugh, plywood is so expensive. It's twice the price of OSB. But maybe I should just accept it for the piece of mind. Hard to know what the right call is.

[eightamrock]

Source of the post

Source of the post I used plywood in my build for the reasons you mentioned and also more mass. I have 1 plywood, 2 5/8" layers with green glue on all layers.

I recommend plywood over OSB because it holds screws better and its a bit denser.

Thanks for your input!

Ugh, plywood is so expensive. It's twice the price of OSB. But maybe I should just accept it for the piece of mind. Hard to know what the right call is.

Haha the right call is usually the more expensive or more work option. My budget was $50k and I stopped tracking around $75k. 3 years later, I am very very satisfied with my isolation levels.

[Starlight]

Hey colliderman, I do not want to cause more uncertainty into your plans but if you have a look at my studio's build, Private studio in Slovakia, especially the photos in post 50, here, you can see how well 18mm OSB serves as the base layer behind all the plasterboard, walls and ceiling. My opinion is that plywood is over-engineering the base layer and, as you say, it is about twice the cost of OSB.

OSB is 640kg/m3 and plywood can vary between 500-700kg/m3, so there is not much in it between the two woods as far as benefitting from extra mass.

[gullfo]

depends on the OSB product and your locale. some OSB is sufficient, i tend use it on walls, but prefer plywood on the ceiling. this way you should have better support for heavy stuff above. unless you can get good quality OSB (which in the US tends to be lower quality than plywood).

[colliderman]

Source of the post Hey colliderman, I do not want to cause more uncertainty into your plans but if you have a look at my studio's build, Private studio in Slovakia, especially the photos in post 50, here, you can see how well 18mm OSB serves as the base layer behind all the plasterboard, walls and ceiling. My opinion is that plywood is over-engineering the base layer and, as you say, it is about twice the cost of OSB.

OSB is 640kg/m3 and plywood can vary between 500-700kg/m3, so there is not much in it between the two woods as far as benefitting from extra mass.

Hey Starlight, thanks for your input!

I agree that the plywood is unnecessary if my end goal is just to have a substrate to attach things to, and so my only concern with OSB is the off-gassing. Normally I wouldn't be super concerned with things like that but I have some first hand experience of how bad it can be when I used it in a bedroom and so I don't want to repeat the same mistake and regret it.

The thing about the studio though is that it's going to get covered by a layer of drywall and caulked and sealed air-tight. So maybe it won't be so bad? I'm just not sure if the layer of drywall is enough to trap the chemicals that come off the OSB. And even if so, it's still just kinda masking the problem. I don't know, maybe I'm being paranoid.

Did you have any issue with the off-gassing from the OSB you installed? I know it supposedly dissipates over time but it's hard to know how much and how long it has an impact for.

The other issue with OSB is that, at least around here, it's impossible to get 5/8" OSB that isn't tongue and groove. I'm thinking that's going to be a real PITA installing tongue and groove on the walls and ceilings. I'm not even sure how I would..

But then the issue with 5/8" plywood (other than the cost) is that it's not as dense and so my overall isolation will suffer.

Ugh decisions decisions! I may just scrap the idea of and OSB or plywood first layer and go all 5/8" drywall and then just deal with how to affix treatment to the walls and ceiling down the road.

[Starlight]

Source of the postDid you have any issue with the off-gassing from the OSB you installed?

I had no off-gassing from the OSB or anything other than the rolls of fluffy insulation, so from my perspective I would tend to think that you are being a bit paranoid, but your experience says otherwise. Glenn hit the nail on the head when he said:

Source of the postdepends on the OSB product and your locale.

Can you ventilate the room for a day or two or get the plasterboard on quick enough that you won't be affected by any off-gassing?

Source of the postI may just scrap the idea of and OSB or plywood first layer and go all 5/8" drywall and then just deal with how to affix treatment to the walls and ceiling down the road.

I really don't think that will be the right solution. In my unfinished studio all the ceiling acoustic treatment (30cm deep fluffy insulation all over the ceiling) is sitting on the drop ceiling which is mounted to the walls. I would not trust that to plasterboard alone. I must correct my comment above about using 18mm (3/4") OSB. I have 15mm (5/8") and all is well. I also have an extra 70kg cloud overhead, from where I sit to almost the front wall plus some extra bits, and these all hang from the ceiling. I would be worried about the safety of all that hanging from plasterboard alone. Your design will likely vary from mine but I am certain that without any wood backing you will have a challenge ahead of you.

I just flicked through my photos and spotted the interior baffle boxes; there is 92kg hanging off the ceiling in those two boxes alone.



Be wise, use a wooden base and either wear a mask, ventilate the room or get the plasterboard up and caulked quickly, whatever will work for you.

[basscleaner]

To my opinion, based on experience, it's better to use Techsound 70 - heavy membrane layer between drywall panels. It ensures the same mass (for 4 mm thick T70) and less construction thickness. For instance, OSB 1/2" has the same weight like for T70 layer 4 mm. But at reducing of full construction thickness. It may be important for the room space economy. I know nothing about price comparing, but guess T70 may be some more expensive. But anycase, formaldehyde emanation from OSB for me is evident.

[colliderman]

Thanks for all the advice everyone. I'm still really on the fence about the OSB because of the chemicals.

I'm also having a hell of a time finding it in square-edge (not tongue and groove). I've called three different big box lumber suppliers and they all told me that no one carries 5/8" in square-edged, it's all tongue and groove, and they'd have to "go to market" to order it, which none of them seemed too interested in doing. I'm in Ontario, Canada btw.

So it seems like everything is working against me obtaining it at all. Maybe it's a sign I should just stick to double 5/8" drywall

Starlight, if I was to go that route I'd definitely be affixing my treatment to studs, not just the drywall. It'll be tough to always find the studs where I need treatment, but I can probably find ways around it. One thought I had was attaching a sort of track system so that my panels could hang off that and I could even move them around to change the sound of the tracking room for example.

[gullfo]

or use 1/2" plywood + 2x 5/8" GWB.