I'm thinking of adding insulation and covering with drywall. The wall is about 7 ft. high and 8 ft. long. Presently it has 2 inches of white rigid foam covered by drywall. I was thinking of gluing 1.5" of rigid foam onto the drywall and putting new drywall over it. Would it pay off.
Answer:
My fear is of the air gap between the layers. I'd tear out the old rigid foam as it is only R-6 or so, and insulate as follows; When insulating any below-grade masonry wall it is best to build (in place) a 2X4 structure with studs 16" O.C. and pull it an inch and a half from the wall in order to accommodate R-20 fibre insulation without compressing it. The insulation actually goes from the sub-flooring above to within eight inches of the concrete floor and so does 6mm polyethylene vapour barrier. In areas where frost is a problem, it is important that drainage at this point not be impeded. Drywalling over top of that would be about the best. Put your drywall up horizontally and you'll save a lot on taping and jointing.
