Basement foam board insulation and wood studs
I appreciate the great articles on basement insulation. I have a question about one method suggested by my local supply store. They recommend gluing rigid foam insulation to the concrete basement walls, and then screwing wood studs on top of the insulation to the concrete wall, with the 3.5 inch side of the stud parallel to the wall. They said there are now rigid foam insulation panels pre-notched at the ends to accommodate the studs, so the stud spacing would be four feet, and the stud would be flush with the foam board once installed. They said the drywall can then be screwed to the studs and wall. Has anyone heard of this and if it will “work.” I don’t want mold! I’m worried about the thin portion of the notched foam where the studs are placed not providing enough insulation and allowing condensation. Thank you
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Replies
There is no reason to use 2x goods for the furring- 1x4s spaced either 16" or 24" o.c. on which to hang the gypsum board works just fine.
With notched 4" EPS for a standard studwall works fine, but that's only sufficient performance to meet IRC 2014 code minimum performance in US climate zone 4A/B or lower. For zone 4C and 5+ it doesn't cut it, but 2.5" of foil faced polyiso or 3" of roofing iso (often available for super cheap in the reclaimed materials marketplaces) under furring does. If polyiso keep the cut edges off slab (above the high tide mark if the basement has a history of flooding) to avoid any potential for wicking moisture into the foam.
Chris,
There are several manufacturers who make rigid foam products that are either notched for furring strips (Owens Corning makes Foamular Insulpink XPS designed to take 1x3 furring strips, for instance) or with some type of embedded studs (for example, InSoFast EPS panels).
As Dana Dorsett pointed out, the main issue with these products is choosing a product that has an R-value that matches or exceeds minimum R-value requirements for codes in your area.
thank you both