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I have a garage that is attached to my house on one side (side shown in the picture). I want to frame and insulate the walls, but I want lose as little space as possible (since the garage isn't very large to start with and the opposite wall has only 2 inches clearance between garage door rails and wall).

Can I frame the walls with 2x4 on the flat edge (Tapcons into the brick/cinderblock, maybe glue as well), and then install 2" thick foam board insulation?

I want some kind of framing, so I can hang things if needed, and possible finish the wall down the line.

I tried looking it up and couldn't find any questions where the person had them attached directly to a sturdy wall.

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  • You're going to be drilling into the wall for anchors. If you own the tooling for this, then the 2×4s seem unnecessary. Instead you might pinch insulation between the exterior wall and plywood or OSB. Install the anchors intended for the 2×4 into the plywood or OSB. The plywood or OSB will hold most hangers. You can fasten drywall to the plywood or OSB to finish the wall.
    – popham
    Dec 5, 2023 at 16:17
  • Would I be able to get away with glueing the 2 inch foam to the wall directly and then 1/2 inch osb/plywood. I dont hate this idea, although, i'd be interested in pricing out the difference in cost.
    – HomeinPA
    Dec 5, 2023 at 16:40
  • You could also glue drywall directly to the insulation to save a buck and a hair's breadth of thickness. Just keep the bottom edge up off the floor an inch or so. I have no idea what adhesive to recommend, though.
    – popham
    Dec 5, 2023 at 16:48
  • As per thisoldhouse.com/insulation/21195484/… yes, you can do the job with no framing, just glue/foam/glue/drywall. But that will impact the way to attach (or whether you even can attach) anything to the walls. A plywood/OSB face or that under 1/4" drywall will solve that one.
    – Ecnerwal
    Dec 5, 2023 at 16:59
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    Are you planning to HVAC the garage?
    – Huesmann
    Dec 6, 2023 at 15:43

2 Answers 2

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Yes, you can use 2x4s on the side as framing. (Or other sizes can work as well, see isherwood's answer.) But a few caveats:

  • A 2x4 is actually 1.5x3.5. So you would only get 1.5" for insulation.
  • Foam is relatively flammable. Whether or not it is dangerous when hidden inside walls, I would not recommend it in any significant quantity exposed, especially in a garage. The usual solution is to cover it with drywall. That will cost you an extra half inch, but will give you a finished surface, which will be better in a lot of ways. Since the drywall is not serving as a firewall (the brick is already doing that), you don't have to do a full tape/mud/finish/paint/etc. job. Bare drywall screwed into the 2x4s to cover all the insulation is really all you need. Proper finishing can be a future project.
  • Insulation is far more important on the outside walls. The wall that is a wall of your house really doesn't need it, though if you are going to bother with 2x4s (to hang stuff) and then drywall (to give it a smooth finished wall) then insulating at the same time doesn't add much to the cost.
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    Good to know for the exposed foam board, It probably wont be too much effort to slap some drywall on it. especially if I can get away with not taping/mudding it. I am starting with this wall because I have to do this project in parts, and its more prudent to get the wall thats sucking warmth from the attached room insulated first.
    – HomeinPA
    Dec 5, 2023 at 16:36
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    But, @HomeinPA, if you start with the exterior walls, then the garage will be warmer and it won't suck as much heat from the house. Added bonus: It's nicer to work in there, summer and winter.
    – FreeMan
    Dec 5, 2023 at 16:57
  • Yes you are right. and that is the overall goal. But If you look in the picture. The two non-brick sections where the windows used to be. are both the backs of built-in shelves and are like 1/8 inch plywood. Im guessing they are the biggest contributors to the heat exchange.
    – HomeinPA
    Dec 5, 2023 at 19:08
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Furring strips are a common strategy and you'll find many related questions on this site.

Why would you waste all that wood, though? a 2x2 (1.5 inches on a side) is more than adequate, and if you want 2" you could rip a 2x6 into two boards and install them on edge.

Note that a wall's insulation value is taken as the average of the R-value across its area. Wood is a less effective insulator, and joints reduce R as well. Consider 19.2" or 24" centers (or the metric equivalent) to save wood cost and improve insulation.

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    "if you want 2" you could rip a 2x4 into two boards and install them on edge" - a ripped 2x4 would be slightly under 1.75" (half of 3.5" and accounting for kerf). Considering the hassle of ripping 2x4s, if I wanted more than 1.5" for insulation I'd go with 2x3 on edge (giving 2.5").
    – Eli Iser
    Dec 5, 2023 at 18:23
  • Gah. Brain cramp. Thanks. Are you proposing 1" and 1-1/2" sheets? That's an odd size.
    – isherwood
    Dec 5, 2023 at 19:00

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