Can you use Rockwool mineral wool as skirt insulation on a slab on grade?
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Can you use Comfortboard mineral wool insulation as a skirt on monolithic slab?
Eric Sokol
Oct. 16, 2021
I am building a small structure on a monolithic slab and trying to reduce the amount of foam in the assembly. I'm wondering if I could use comfortboard sheets as my horizontal frost protection skirting on the outside of the slab? It is an 18x16 slab, on a very well drained crushed stone pad. Roxul tech support was not very helpful with this question (she seemed unfamiliar with the detail), so I am wondering if anyone has had experience with this? Thank you!
Yes, you can useRockwool comfortboard mineral wool insulation at foundation skirting.We did just that on our2015 demo house project, and the company wasn’t a whole lot more helpful at the time for us either. Slab on grade foundation insulation is not a market they seem interested in competing in. They told us it *should* be fine, and that in their mind the only risk was if there was heavy rain in the fall followed by a quick flash freeze, so we eliminated that risk by laying a poly membrane on top of it. The concern was that if it was saturated by water and froze before it completely drained through then it could be rendered effectively useless. But when covered with a poly barrier (or any waterproof membrane you have), water will run right off without a problem.