My house was built in 1912. The studs measure true 2x4". I live in iowa....a "cold" climate. I'm looking to completely fill in stud cavity with insulation. Can't find batting that measure 4" thick. Can only find 3 1/2x15" batting. Could I install a 1/2" foam board in stud cavity against outer sheeting sealing with foam sealant around perimeter and lay kraft faced fiberglass batting against foam board to accommodate the 4" needed? I'm confused on the vapor barrier rules as far as the do's and dont's. I am not looking to spray foam the cavities due to budget restricrions... Any help would be greatly appreciated. Thank you!