Rigid foam on an interior basement wall with exterior rigid foam present
Hello,
I’m looking to finish my basement … it currently has 2″ of XPS rigid foam exterior to the concrete foundation wall along with 2″ completely under the basement slab and a poly break between the footings and foundation walls. I would like to add additional insulation to the interior of the walls such as 1 1/2″ of XPS rigid foam prior to framing interior walls. Is it ok to sandwich the concrete walls foundation walls with rigid? … almost like an ICF although not as tightly applied on the interior as the finish on the foundation walls is in the form of a brick pattern (i.e.. not smooth). If so, is it best to affix them with a rigid foam friendly adhesive (press fit with seams taped) or mechanically attached in areas with the Hilti type anchors. Also, the height of the rigid foam needed is around 8′ 8″ … just shy of 9′ … is there a recommended product available in a 9′ or 10′ height that’s easy to work with? Please advise.
Thanks,
– Milan
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Replies
Milan,
Q. "Is it OK to sandwich the concrete walls foundation walls with rigid foam?"
A. Yes. As you point out, this is similar to an ICF wall.
Q. "Is it best to affix them with a rigid foam friendly adhesive (press fit with seams taped) or mechanically attached in areas with the Hilti type anchors?"
A. Either way will work. If you use adhesive, you need to come up with a way to apply even pressure until the adhesive sets. (One approach is to apply pressure with scraps of plywood or OSB, held in place by long 2-bys that are wedged to the opposite wall.) Since your concrete is not smooth, make sure to air-seal the perimeter of the rigid foam with canned spray foam or generous amounts of caulk.
Q. "Is there a recommended product available in a 9' or 10' height that's easy to work with?"
A. Inquire locally. Where I live, I'm limited to 8-foot rigid foam, but I know that longer lengths are available.