Stem wall insulation
We are just about to begin construction on our new home. Our exterior wall is designed to be (from the outside to inside) clapboard siding, strapping, felt paper, 2″ polyiso, plywood, 2×6 wall with denspak cellulose, drywall. It is going to be slab on grade construction with frost walls. We are insulating under our slab with 4″ of insulation and including a 2″ thermal break between the slab and frost wall at the slab shelf.
We are waffling between the following:
1.) Using 2″ of XPS on the outside of the stem wall
2.) Using 2″ of XPS on the inside of the stem wall
3.) No stem wall insulation
Factors we’re considering
– maintenance/aesthetics of the stucco type coating for option #1
– whether or not to offset the exterior stud wall into the foundation by 2″ if we go with option #1
– one of the details in the GBA library shows no insulation on the stemwall – is this really a good option?
Any thoughts are appreciated,
heidi
GBA Detail Library
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Replies
What is your location? You may or not be required to install insulation.
We are zone 6...
I should correct the second consideration to read "- whether or not to offset the exterior stud wall into the foundation by 2" if we go with option #2"
Thoughts?...
Heidi,
I urge you strongly to insulate your stemwall; I would say that 2 inches of XPS is the bare minimum, and more is better.
Either detail will work, so discuss both options with your builder and choose the easiest way for your team.
Martin,
Agreed, we had already moved passed Option 3 (no insulation).
Our builder is fine with either approach, but likes the benefit of not needing to maintain a stucco coating by placing the insulation on the inside.
I just wonder if there is any significant energy penalty by moving it to the inside and not having that exterior layer of insulation be continuous down to the footing?...I can't seem to find any strong opinions for either case.
Heidi,
Various methods exist to avoid a thermal bridge under the wall's bottom plate. I hope that a GBA reader can post a detail so that I don't have to describe your options.