Can non-foam insulation (rock wool, fiberglass) be used as above slab under sub-floor insulation?
Hello, I am in the process of building an insulated subfloor on top of a slab on grade. Currently the plan is 6 mil poly, sleepers to correct the unevenness of the slab, with insulation between them, and 1 inch tongue and groove fixed to the sleepers. Unfortunately the slab doesn’t have any insulation below it – but is insulated around the perimeter and has a vapor barrier and a draining layer below it. According to https://www.greenbuildingadvisor.com/question/insulated-floor-on-top-of-concrete-slab#
the best choice of insulation in this situation is foam board or spray foam insulation.
My question: I have been given quite a lot of insulation made from recycled pet bottles. It has similar insulating properties to rock wool. I Would like to fill the 4inch cavity in the sub floor with this rather than than eps or XPS. The climate I live in very rarely gets below freezing and the summers are hot and humid. Would using this sort of insulation create unwanted problems?
I have attached a picture of the slab and gap
i would like to fill.
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Replies
Jun,
If you wanted advice on the best way to proceed, here's what I would tell you:
1. Install self-leveling compound to make your slab level.
2. Install a continuous layer of rigid foam, without any sleepers, as insulation. Depending on your R-value goals, this could be about 2 to 4 inches thick.
3. Install subflooring (OSB or plywood) above the rigid foam, and fasten the panels to the slab below with long Tapcon screws.
That would be the best way to proceed. Then you could sell the unneeded polypropylene insulation on Craigs List, or perhaps you could use it to insulate your walls or attic.
Thank you Martin.
I understand the idea of best practices and will most likely follow your advise. The main reason I'm asking is the expense of installing a continuous layer or rigid foam (budget restrictions...blow out). With 4 inches of polyester batts installed on a poly sheet, the R value would meet the minimum requirement for my climate zone. Aside from the drop in overall efficiency of the floor, would this type of installation be more likely to have moisture issues?
Thanks again