Rigid mineral wool under garage slab
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
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