Airtight drywall in CZ 3A/4A
tjones1014
| Posted in General Questions on
I’m confused about whether or not to make the interior drywall airtight, thus acting as an interior air barrier. Here’s our current setup:
Hardie
Benjamin Obdyke Slicker MAX rainscreen
Tyvek commerical wrap
OSB, taped seams
2×4 stud wall
rockwool insulation
drywall
I’m in the N GA area, so we have hot & humid summers and can have relatively cold winters. I’m confused about whether or not making the drywall airtight is a good idea in my CZ. We have the taped OSB seams, so we have an exterior air barrier. Do we also need one indoors?
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Replies
tjones,
Air-barriers anywhere in a wall are a good idea in every climate. It's the location of vapour-barriers that can become problematic.
When your primary air-barrier is the sheathing, the secondary interior one helps stop moist interior air from moving though the batt insulation and coming in contact with the OSB. Drywall, with no additional sealing, is enough to do that.
So if I'm understanding correctly, I don't have to seal the drywall to the bottom plates, correct?
For a tub on an exterior wall, do I need to seal all the edges (including the bottom plate), or does the same principle apply here as well?
tjones,
With the primary air-barrier being the sheathing, any sealing you do to the drywall is useful but not essential. In the absence of drywall, the area behind a tub should have another interior air-barrier. A Membrane or house-wrap will do.
We ended up using 1/4" cement board and plan to make it a continuous barrier from top to bottom. The seam at the bottom was tricky to try to seal with caulk so they ended up caulking the cement board, bottom plate,and slab together (pic attached). Is that ok, or is it setting us up for any issues?
tjones,
No it’s fine.