I live in an 82 year old house with a basement. The first floor is made using junior beam construction -- steel i-beams set about 30 inches OC with poured concrete about 4 inches thick. The i-beams are about 10 inches in height which creates a stud bay about 6 inches deep under the floor (on the basement side).
Part of the floor is over an unconditioned integral garage which brings me to my question about insulation. The room above the garage is conditioned. I live in a zone 5 climate. I'd like to use Roxul rockwool batts which has a 5 1/2" thick batt.
Should I install a vapor barrior on the cement side of batts?
I'd appreciate any other advice on the installation as well.