First – climate zone 6B – pretty good home – 3″ of exterior polyiso on walls – Roof is unvented – ccSPF under the roof deck and rafter cavity filled with BIBS fiberglass.
It is clear from my thread here:
that I did not fully understand the airtight drywall approach. So this post is to help me verify that now I understand.
It was my original understanding that airtight drywall was all about just sealing the drywall to each other, to the floor and to the roof and that it was the interior surface of the drywall that is the sealing layer and thus every room and wall internal and external would all have to be sealed. Thus I couldn’t understand why I needed to seal double top plates or really anything outside of the drywall.
Now I realize it’s the outside of the drywall that is the sealing surface. Therefore interior walls only need have the sheetrock sealed to the top plate to prevent air leakage throught eh stud cavity up into the rafter cavities.
I understand the “not lifting you pen” off the paper when drawing your air barrier, which is easy to do on a simple cross section, however some cross sections of my home are quite complex.
Shows sealing the drywall to every stud. How important is that? It seems other advice says only to seal it to the top and bottom plate. It also shows he used a can of spray foam to seal the edges. I thought that if you taped and mudded the drywall then that was a good air barrier and spray foam is not necessary?
Here are some of my learnings, feel free to correct me if I’m wrong:
1) Airtight drywall primarily applies to exterior walls and ceilings.
2) Internal walls don’t need air sealing except along the top plate where it connects to the roof rafters to prevent air in the stud cavity going into the roof rafter cavity.
3) Internal walls on a lower floor (floor above is within thermal envelope) don’t need to be sealed on top or bottom plate. If air leaks out the the top of the stud cavity it is stopped at the band joist sealing (which in my case is ocSPF).
4) All the vertical joints between king studs need to be sealed.
5) First stud in an internal wall that adjoins to an external wall needs to be sealed.
6) It’s super important to air seal living space above a garage.
Attached are a few pictures of my construction. A few of the pics have a few questions too.
Advice corrections and help is much appreciated,
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