I plan to renovate an open area of ~900 ft² (84m²) within a well-built horse barn. I'm located in Quebec, where we can get winter temperatures down to -40 (C and F) -- but typically more like -25C (-13F) and very dry -- and summer temperatures up to 35C (95F) with high humidity. I hope to install radiant floor heat in 3 zones to make the space usable in any season. The exterior walls have the following (from the outside): steel siding; black cladding paper; ½" (13mm) plywood sheeting; 2x6 stud walls with 6" of glass fibre insulation; a plastic vapour barrier; then interior cladding of 2" T&G hemlock. I have two questions related to avoiding moisture buildup: 1) For the finished interior, can I put drywall directly over the T&G without creating a moisture problem? The hemlock has been in place for >20 years, so is probably now as dry as it will get. 2. If I decide to upgrade the insulation by adding a layer (either new stud walls or foam panels), I would prefer not to have to remove the T&G. However, if I do add insulation inside, I'm concerned about causing moisture to build up within the hemlock. Is there an insulation solution that would not involve removing the T&G boards?