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I've recently had to remove existing drywall and insulation in my condo in Ontario. Now I need to finish the walls.

I was thinking of:

  1. Gluing 2-inch Durafoam to the concrete
  2. Putting in the proper framing
  3. Adding 3.5-inch fiberglass batt
  4. Adding a vapor barrier
  5. Drywalling on top of all this

Am I out to lunch? Feel free to make fun of me if I am. Is my method off base? I've been reading stuff about double vapor barriers being bad because there is a cement wall etc.

Exterior facing wall

  • Is this above or below grade? – isherwood Jan 9 at 18:58
  • The answer may help to determine where the vapor barrier goes, or if one should be put in at all. – SteveSh Jan 9 at 21:54
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I would glue durafoam to the concrete first like you said.Then like you said put up a wall using 2x4s for the 3 1/2" insulation. Then use unfaced insulation,then a vapor barrier then the sheetrock. If you want to use paperbacked insulation then do not use a vapor barrier afterwards before putting up the sheetrock. If you put up two vapor barriers there will be a strong possability of trapping moisture between the vapor barriers. And moisture means mold.

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    Are you sure you want the vapor barrier on the inside side of the wall assembly? That is a surefire recipe for condensation inside the wall as soon as you flip the air conditioner on... – ThreePhaseEel Sep 22 '18 at 5:19
  • But if you put the vapor barrier against the concrete wall, don't you have the potential for condensation inside the wall (on the inside surface of the plastic) during the heating season? – SteveSh Jan 9 at 22:19
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No you are not out to lunch, but you should not put in the vapour barrier. The rigid insulation is an air/moisture barrier, and you should tape the seams to make it a comprehensive seal. Then you can frame and use bat insulation for extra insulation. The extra vapour barrier is at best an extra expense, but you also run the risk of trapping moisture behind it in the bat insulation and causing mold problems.

It looks like the electrical box does not protrude too far so I would guess the original wall was not very thick. You might consider framing a 2x3 wall, but that would mean less insulation of course. Ideally 2 inches of rigid foam should be used, so combined with a frame wall you will lose floor space. You might also consider strapping and drywall alone against the rigid foam, but that would also obviously reduce the R value and the amount of space for electrical.

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