GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Rigid mineral wool under garage slab

mssusr9501 | Posted in Green Products and Materials on

Trying to use Rockwool Comfortboard 80 under a new garage slab but man it is hard to get and expensive in my area.
I am in western Michigan.  Local building supply has minimum buys and increments of a pallet.  Naturally I need more than one pallet so would have to buy 2.  For 2 pallets of 2 inch 2×4 Comfortboard 80 they want around $3200 plus tax.  A pallet is 720 square feet
They stock Thermafiber and insinuated it would be cheaper but the Thermafiber does not explicitly state that underslab is an accepted use.

I would prefer not to use foam but that seems to be what the local supply houses stock.

This garage bay addition is insulated and will mostly be used as my workshop rather than vehicle storage.  I was planning to put 4 inches under slab and 2 inches around perimeter.  Figured I needed 888 square feet

What alternatives are there?
How can I get the cost of the rigid mineral wool down to a more reasonable level?

Thanks for any suggestions or comments

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. brendanalbano | | #1

    This is perhaps too obvious to even suggest, but if you only put 2" under your slab, would that get you under 1 pallet's worth? It sounds like that would save you about $1600 if you didn't need to buy the second pallet.

  2. hydronicnerd | | #2

    Just today got a quote for R12 Comfortboard 80 2' x 4' x 3" $2.068/sq' (528 sq'/pallet). ~$1100/pallet. Perhaps another vendor?

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |