I plan to insulate my basement (poured concrete). Someone suggested putting tarpaper on the walls, building the frame and adding bat insulation (R?) both 1" from the wall to allow for air circulation with a vapour barrier over all. The insulation would go down to 8" above the floor and the VP 2" below that that as you recommend. Do I need tarpaper and should go to the floor? Do I need the 1" space between the frame/insulation and the wall? I have no water problems but do have a light musty odour.
Answer:
I wouldn't use the tarpaper unless local building regulations demanded it. 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 bats without compressing them. I prefer not nailing anything to the concrete floor. I’d rather concrete nail (ram set) a 2X4 plate every three to four feet, a foot or so down from the top and another a foot or so up from the floor to the wall all around the room and toe-nail the studs to them. This permits an extra inch-and-a-half space so the 6" insulation bats can be applied without being compressed (compressing loses R value). You’ll still need both top and sole plates but neither of them is affixed to the top nor bottom because the ram-setted straps will give it more integrity than anything else could. For attaching the top plate, you can use 3" drywall screws at an angle - like toe-nailing. The insulation actually goes from the sub-flooring above to within eight inches of the concrete floor and the 6mm polyethylene vapour barrier goes two inches lower so it can be pinched and stapled to each side of each stud. This keeps the insulation bats from sliding down and at the same time, the system avoids a lot of condensation problems. It also permits a bit of heat loss to the drainage tile along the exterior perimeter of the footings. In areas where frost is a problem, it is important that drainage at this point not be impeded.
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