Drying Potential of Plywood Behind Drywall
rhl_
| Posted in General Questions on
I’m opening some walls to install some insulation and some new heat pipes and I discovered that some bays in one room have 3/4” plywood directly behind drywall.
this seems suboptimal for interior drying, is it?
certainly for insulating..
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> this seems suboptimal for interior drying, is it?
Perhaps not that big of a deal. From an APA website (https://www.performancepanels.com/permeability): "For example, at 50% humidity the water vapor permeance of plywood is approximately 1 perm but the water vapor permeance may be increased by a factor of 10 when the humidity is increased to 90%." So maybe plywood 'does the right thing' when it needs to.
> certainly for insulating..
This point I don't understand. It's certainly not worse than drywall directly on the studs. Most conservative estimates of the R value of wood I've seen are around R-1/inch. In reality, this is obviously species dependent. It's not great but it's also not 0. By definition, it's therefore not worse than drywall alone.
Be careful with plywood walls, these could be shear walls, removing them will compromise the structure.
I've dealt with some projects where the client requested continuous plywood behind the interior gypsum board finish, so that they could hang their artwork anywhere they wanted. Taking a look at plywood properties (see "The Magic of Plywood and the Modern Residential Wall" in the link below), it actually behaves somewhat close to a smart vapor retarder... relatively vapor closed at low RH, and very open at high RHs. So on the scale of things, not an issue.
BSI-038: Mind the Gap, Eh!
https://www.buildingscience.com/documents/insights/bsi-038-mind-the-gap-eh
Ok that’s great, thanks everyone.