Best Practice for double stud wall over ICF foundation?
Hi All,
I’ve attached a rim joist detail that I’ve taken from the PGH book. The rim joist has 2″ of continuous foam on it’s exterior, which is flush with the layer of 2″ eps on the exterior of foundation. The sub floor and the studs above hang over the edge of foam so that the sheathing goes over the framing and foam. This is all pretty straight forward in the image.
This is basically taking the 2 x 6 framing members and turning them into structural 2 x 4 members as a part of the 2 x 6 is cantilevered. I am wondering if there is a better way to achieve continuous insulation around rim joist exterior while avoiding this overhang? I’d like to use 2 layers of 2 x 4 framing material for my double stud walls if possible. I also do not intend on extending 2″ of EPS foam to the trusses as I intend on doing a double stud wall instead of an outsulation style build.
I appreciate any input – thanks.
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This diagram appears to detail the exterior wall as load bearing. Assigning the interior wall as load bearing would simplify load paths.
Attached is an image of what my architect and I came up with. Basement is ICF with an additional 2” of foam on the exterior. Floor trusses bear on concrete with the interior 2x4 load bearing wall bearing in the trusses. This allows for a flush exterior and a large quantity of continuous insulation.
I think the OP's detail is really the best way to go.
You can make the inside wall load bearing but this brings complications with it such as needing let in bracing. It is also not easy to stand up the outside wall because of the height difference form the floor. The interior bearing wall also limits your sequencing as all the walls have to be built, whereas if you go with an exterior load bearing wall, you can get the outside up and roof on, once dried in the interior walls can be built.
The one benefit of JMRtbay's detail is more rim joist insulation though.
To the OP, I really don't see much difference between a 2x4 or 2x6 wall on the outside. In terms of assembly R value, it barely changes anything if the interior studs are not aligned and the cost delta is pretty much noise.
Thanks for your input. Are you suggesting that my interior 2 x 4 wall should have a different stud layout than the 2 x 6 exterior wall?
I think it will have a different layout by default. On the outside, the on-center spacing will follow the sheathing, on the inside drywall. So unless you go out of your way to align them, they won't align.
Caveat here is that if you want to use batts, either align the studs or install the interior wall after insulating the exterior one. It is a PITA to fish batts between staggered studs. If you are dense packing, it doesn't matter.