We offer R14 rigid foam board insulation under the subfloor of your custom shed, cabin or garage. Combined with proper wall and ceiling insulation, your building can stay toasty warm in the dead of winter. Current price for adding foam board floor insulation is $4.50 per square foot. We can add this to any size building. For buildings 12x32 or larger, we can use closed cell spray foam insulation instead of the rigid foam board. Spray foam is superior in its ability to seal all the gaps and cracks and cost a little more at $5 per square foot at 2" thick.