We would like to insulate and drywall the garage walls to work on projects in the cold winter and hot summer. (We'll probably install a mini-split or something similar, too.) This question is specifically about the walls (but see this question about the ceiling).

The walls are bare-stud uninsulated 2x4's and all work will be done from the inside.

This reference says that if exterior siding is removed to "Drill holes in the sheathing and blow insulation into the empty wall cavity before installing the new siding, and ... add R5 insulation wall sheathing beneath the new siding" ... but we are not removing the siding.

Question: What is the best practice to insulate (and drywall) the walls in situations like this?

Picture of the existing walls:

2x4 walls

  • 1
    Do not forget to insulate the ceiling and the big door, those are your biggest heat loss points. Before closing it I would also suggest you prewire it with at least #12 (20A) so you can install GFCI, and duplex outlets in the future. If it will be a shop add more or even a sub panel. You will have to install wire with the split anyway. I did mine with several circuits.
    – Gil
    Oct 3, 2022 at 16:01

2 Answers 2


I think the 'best practice', at this time, is to use closed cell expanding foam sprayed between the 2x4's and then trimmed flush with the 2x4's. You add drywall after that.

That will give you the highest R value but is pricey.

They use it on This Old House quite often.


You could also using furring strips to increase to 2x6, then install insulation. You'd get a lot more insulation without breaking the bank on spray foam, but you're not going to hit the same R value as spray foam.

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