2-part spray foam: Store-bought kit or professional application?
New home build in CZ 6A. While discussing my cellulose insulation requirements with a local supplier, he tried to sell me on spray foam for both the rim-joist and below-slab in the basement in addition to the cellulose for my walls. I explained to him that sub-slab spray foam was likely out of our budget and that if I did spray foam in the rim joists it would only be a thin coat for air sealing purposes, and that I would probably do it myself with a store-bought 2-part foam kit.
He made some claims to back up his argument:
1. He claims sub-slab foam is a superior way to go, and that no EPS panel job would offer the same continuous layer or air tightness.
2. He claims that store-bought 2-part poly foam is inferior in quality and performance to what the professionals are using, and that he’s been called out to “many” jobs where this inferior foam has had to be removed and re-done by his team.
I didn’t argue with him, but my thoughts are:
1. Spray foam could cost MUCH more per R/sqft (he claimed about $3/sqft for R10) than an equivalent EPS foam board installation below slab, and this could be significant in a 1700 sqft basement. Also, judging by the spray foam wall jobs I’ve seen, the inconsistent applied thickness of the foam could lead to widely varying concrete slab thickness unless considerable effort was put into leveling it before the pour.
2. A friend of mine is using Dow Froth Pak 2-Part poly foam to do his home’s rim joist area, and he’s impressed with it. I read up on the product and it gets excellent reviews, is not prohibitively expensive, and it’s an R6/inch closed cell foam. If care was taken to ensure a proper installation I would think this foam would work well, no?
Are my thoughts reasonable, or does the insulation guy have valid points?