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Community and Q&A

Framing and Insulating Basement Exterior Walls

Luke_O | Posted in General Questions on


I live in Minneapolis Minnesota and I’m renovating my basement. I’ve seen multiple ways of doing basement exterior walls but never what I’m about to describe and I’m not sure what I’m missing…

Why not use 1 or 1-1/2″ rigid foam continuously against the concrete block on the inside of the house, with a framed LSL wall (on edge to save space – and since there laminated strand 2 by’s they’ll be totally straight) on the inside of that, and then do 24 O.C. in order to save money from the higher cost of LSL’s vs standard lumber, and then do 5/8″ drywall to make up for that.

You’d get a continuously insulated basement, straight walls, it really wouldn’t be that expensive with 24″ O.C. (especially with current lumber prices), and it would save space compared to a traditionally framed wall.

Am I missing anything?

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  1. Expert Member
    Malcolm Taylor | | #1


    That would work fine. The question is whether the 2" you save by not framing the wall conventionally is worth not being to add more batt insulation in the cavities, use regular electrical boxes, and run plumbing.

    1. Luke_O | | #3

      If rigid foam is directly on the foundation wall, is additional fiberglass batt insulation in between studs not going to be a problem at all? I thought generally staying away from batts in the basement was best-practice? Or with the rigid foam layer does it not matter?

      Otherwise, those are helpful concerns. Thanks!

      1. Expert Member
        Malcolm Taylor | | #6


        As long as you make sure the rigid foam is thick enough to stop condensation, you can safely add batt insulation to the walls.

  2. DCContrarian | | #2

    What's your local energy code for basement insulation? I'm guessing R-15 at least. So you'd need 2-1/2" of Polyiso or 3-1/2" of EPS.

    Maybe put pieces of foam between the LVS?

    1. Luke_O | | #5

      Honestly I don't know... It's my own house and anything I do is going to be an improvement, and I'm flying under the radar a bit haha but I should check on that. Yeah that's a good option. I guess I just need to decide how important it is to save space...

      1. Jason S. | | #7

        Cheapest way to get there is 2" EPS and 2x3 frame with batts. You can still do 24" OC.

  3. Deleted | | #4


  4. Hammer 🔨 | | #8

    If you don’t want batts you could just use rigid foam in between like a cutt and coble. If you aren’t running wires inside the wall and it’s not structural you could even use 1x3 or 4 for furring strips. I have also heard of people just attaching drywall straight to foam board with adhesive however these was some worry about adhesive failing.

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