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1950 building — bare block walls, no insulation, no drywall — 1 1/2″ room to improve?

[email protected] | Posted in Energy Efficiency and Durability on

Northern Ill location -8 ” block bare except paint inside and out. Apartment 2 bed forced air nat gas heat New anderson double hung well sealed.
Will put treated 2×2″ interior frame to put conduit for new circuits–only 2 circuits now -kitchen and everything else. flat roof with 2×10 insulated. So do I go plastic vapor barrier then 1 1/2″ sheet foamboard between studs? or just foam board or building wrap over or under foamboard. No AC.

So now condensation point is in block wall and has been forever. If I move it in -will I create a water making machine?

Any Ideas?

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  1. GBA Editor
    Martin Holladay | | #1

    Is this a below-grade wall (a basement) or an above-grade wall?

    If it is an above-grade wall, can you insulate the wall from the exterior? Or are you confined to installing insulation on the interior?

    In northern Illinois (Climate Zone 5), you want to aim for an R-value of R-20 for an above-grade wall. (Check with your local code authority, since codes requirements vary.) With a concrete block wall, the usual approach would be to install a continuous layer of rigid foam. Either 5 inches of EPS or about 3 inches of polyiso would work.

  2. [email protected] | | #2

    It above grade--we need to fasten 2x2 stud to block every 16" for outlets and drywall. If we put continous 3" foam then 2x2 wall-it would be a big fastener and increase the depth to trim out windows?--in Future we may put siding on outside with more 2x2,s but not for a couple of years.

  3. [email protected] | | #3

    I am mostly concerned with actual water dripping inside new wall on floor--

  4. GBA Editor
    Martin Holladay | | #4

    If this were my project, I would aim for at least R-20, as I noted in my first answer, even if I had to buy long fasteners.

    That said, if you want to skimp, and you decide to only add R-5 insulation to your wall, you won't get water dripping on the floor (as long as your rigid foam covers 100% of the wall, and as long as your air-sealing details prevent interior air from reaching the cold CMUs). The only problem will be that the building will use more energy than a building that meets minimum code requirements.

  5. Expert Member
    Dana Dorsett | | #5

    There is no need for a plastic vapor barrier anywhere in this stackup.

    At the same wall thickness, rather than 2x2 butted up to the block walls, put a continuous layer of 3/4" foil faced polyiso tight to the block, sealing the seams with foil tape, and use 1x4 furring through-screwed to the block with 2.5-3" masonry screws. filling in between the furring with another layer of 3/4" polyiso It'll still be way below code minimum performance, but WAY better than what you'd have with 2x2 thermal bridging and 1.5" foamboard between the framing.

    To hit code-min would take R13 continuous foam with no-infill, or R10 continuous foam if adding R6-ish infill between furring or 2x2 framing (overlaid on the R10 continuous foam.)

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