Trading Roxul for plastic foam in basement wall insulation.
The usual advice for interior insulation of basement walls is use rigid foam because it is not air permeable so condensation will not occur. Cost of material for foam is near $0.12/ r sq ft. Cost of Roxul comfort bat about $0.045/r sq ft.
I will have an inner basement wall of 2x6 to support my first floor and the inner walls of the exterior double wall. My initial sketch shows 3" foam and R-15 batts with no drywall. If I switch to all Roxul I would want airtight drywall. I already have more insulation than I can justify.
So if I change the plan and use R-10 Roxul for steel studs, installed through the stud spaces and stick with the 3 1/2" in the stud cavities and add airtight drywall will the insulation cost saving pay for drywall? If I can add drywall for less than $1.35/sq ft. the answer is yes! If I also switch to R-23 between the studs adding about $0.32 /sq ft. I'll actually increase the wall R and still more than pay for the drywall.
Since it is required that bottom plates sitting on concrete be treated no damage will occur even if there is some condensation on the concrete wall. I will need to add the step of caulking the bottom plates to the floor to assure air tightness along with all the other ADA steps. Have I missed something?
Posted Mon, 03/11/2013 - 16:31
Edited Tue, 03/12/2013 - 07:03
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