Stepped Wall Layers
Hi All,
I felt like I had a solid plan with both my exterior wall assembly and my interior basement insulation. However, it’s all become a bit more confusing when I look at my stepped foundation wall in the basement that’s currently being framed up. CZ 6.
The wall plan was to do rigid foam CI on the exterior walls over 2×6 studs with fluffy insulation. The basement plan was to do rigid foam against the concrete, foamed and taped, with a 2×4 wall in front with additional insulation.
However, I’m realizing here that where it steps down, I’m looking at a sandwich of insulation. If I were to keep the above plan, I would have exterior rigid > fluffy cavity> interior rigid > more fluffy cavity. I know enough to know that this is a bad look.
So, curious what the solve here is? Off the top of my head, I would assume that where the foundation steps down, I should forgo the the layer of interior rigid and just use cavity insulation that fits the full depth and doesn’t leave an air gap. However, that seems to be a ratio that is incorrect and would cause a dew point issue. Curious what others have done here, as I’m surely not the first.
Photo for reference. Thanks–
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Replies
Sean,
Two suggestions:
- Only frame the interior 2"x 4" stud walls to the height of the concrete outside, so you end up with stepped ledges inside.
- Leave the interior wall empty above the concrete altogether, with all the insulation there in (and on) the exterior wall. If you go that route I'd use faced fiberglass batts on the inside of the 2"x6" stud wall.
Thanks Malcom -- makes sense. Leaving it open probable makese the most sense from an aesthetic perspective. Vapor barrier against the concrete wall in that case?
Sean,
Poly against the concrete does no harm, but the foam is fine without it.
If using fiber faced polyiso, the poly sheet would be helpful. With XPS it wouldn't matter, and with thicker EPS it won't make any real difference either. Basically if the foam itself can't be the vapor barrier (such as with fiber faced polyiso), then the poly can be helpful.
I've used poly behind reclaimed fiber faced polyiso since it's cheaper to get reclaimed fiber faced polyiso, and the poly doesn't add enough material or labor costs to offset the savings from the cheaper reclaimed rigid foam.
Bill