Zone 6 – Best wall without exterior foam
This is a great forum. I’ve been reading a lot over the past year but finally signed up for access to all the additional information.
I need to make a decision about the wall assembly in my 1.5 story new-build house in Climate zone 6a.
My first choice would be to use Zip R-6 with dense pack cellulose in 2×6 walls. I don’t want to go any thicker on the Zip because of concerns about racking resistance.
My second choice is just going with osb/plywood with taped seams or standard Zip system. Then I would do 2” of closed cell + dense packed cellulose in the cavities. This is what several of the builders in my area are doing. But they aren’t using an interior vapor barrier.
In both cases, I would use LP Smartside with a rain screen, taped seams on the zip sheeting (if using zip) or well-installed Tyvek (if using osb or plywood). Well sealed and painted 5/8” drywall on the interior.
I realize these aren’t super high performance, but they are in my budget and my contractor is comfortable executing them.
I’ve read until I couldn’t think straight. It seems that with the small amount of exterior foam I’ll have with either of these options, that I will need to exclude vapor from the wall cavity using a semi permeable barrier under the drywall, to limit condensation when it is very cold outside. But I would like to avoid it if possible. My concern with the interior vapor barrier is that with OSB or especially the Zip R on the outside, it won’t allow enough vapor passage and I’ll end up with a wall that can’t dry.
Once again, thanks to all here. This is an excellent forum.
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