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I live in Chicago and have 50 yrs old house that has attached garage. I found out that the walls in garage does not have insulation. I am planning to open the drywall, put batt insulation and drywall it back.

My concern is moisture here. The reason I am concerned is that the garage walls are built in such a way that half of it is concrete wall and framing rests on this concrete wall. So if I insulate 'til the framing only will it create moisture issue? Or should it be fine?

The reason I want to insulate is because I have room above the garage which stay colder than other rooms in the house. I have checked the garage ceiling and attic and they both are insulated. The only part in garage which is not insulated are the walls. So I am thinking insulating the walls will keep the garage little warmer and in turn the room above will be little warmer than what it is currently now. And by the way on cold day my garage temp goes to 35-40F.

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    Just curious, why do you want to insulate your garage? Is it just the wall between your home and your garage, or are you looking to insulate the entire garage? Feb 9 at 4:00
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    Understood, this is useful information for getting your problem solved. This info will (at least it should) impact the answers you get. You should consider incorporating this problem statement into your question. Feb 9 at 18:54
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    You'd be far better off upgrading the ceiling insulation. Overlay foil-faced iso panels, for example. Unless you heat the garage to nearly indoor temperatures you won't get the effect you're after.
    – isherwood
    Feb 12 at 17:10
  • @isherwood can I use both in the exterior facing wall for the garage. Meaning putting foam board first with sealing it with foam and then put fiber glass on top of it. I searched for it and some people say it will probably trap some moisture over the life of it. So will hybrid approach of foam board plus batt a good idea?
    – Mayur
    Feb 25 at 18:03
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Chicago - Cold. Vapor barrier to inside. Moisture concern solved.

Half-concrete wall - if you only insulate the frame part, the concrete part will still be wicked cold. You might want to consider insulating the frame part and then covering the whole wall (concrete part and stud bays) with rigid foam sheets, taped or sealed as the vapor barrier, and then drywall - which would give you some insulation over the concrete part.

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Given the additional information in your comment:

The reason I want to insulate is because I have room above the garage which stay colder than other rooms in the house. I have checked the garage ceiling and attic and they both are insulated. The only part in garage which is not insulated are the walls. So I am thinking insulating the walls will keep the garage little warmer and in turn the room above will be little warmer than what it is currently now. And by the way on cold day my garage temp goes to 35-40F.

You should look to insulate the room itself - by which I mean look to insulate the walls of the room itself first, then improve the insulation of the floor system, then address the garage below. It's not that it's a bad idea to insulate the garage walls, but the garage door and the slab itself are still going to be too great a thermal suck for an unheated garage.

Go ahead and insulate the walls as long as they're open. It might help a bit if you have the money to throw at it, but pay particular attention to insulating at the top of the wall to continue the insulation plane across the whole floor system, right now it's probably missing at the exterior walls above the top plate and below the bottom plate of the room above.

Solutions in order of greatest impact would be:

  1. Thermal decoupling for the entire building envelope - I know, impractical, but I want you to get a better understanding of what the challenges to solving your problem are, not just getting a "yes you can insulate the walls for some advantage" - this entails installing insulation under your siding, over your sheathing and moving your WRB outboard of the insulation.
  2. Thermal decoupling for the garage ceiling from the floor of the room above - drop the drywall on the ceiling, fasten insulating foam to the bottom of the joists, ensure you maintain fire code before covering, reinstall the drywall with longer screws, tape joints to code.
  3. Air seal and replace the fenestrations, especially the garage door, with a better insulated and better sealed door.
  4. Insulate the perimeter of the foundation, minimum 2' below grade against wall, but in an ideal world with all the money you would retrofit as a frost protected shallow foundation.
  5. Insulate the bays in the garage walls.

So the upshot here is not that you shouldn't insulate the bays in your garage wall - as long as you have the walls open, you should absolutely throw it in there - it's just that there are a lot of factors that could net no noticeable impact despite that time and money spent, particularly that the amount of thermal loss from a room above to the garage below at only 35 to 40 is going to be very minimal. There's something else going on. If you were at -35 or -40, you would see a bid difference, but with your reasonably temperate temps, you should be looking to add to max-out the insulation value of the framing directly around room itself first and foremost to the greatest extent affordable to you.

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Insulate the stud walls with the thickest rolled insulation you can. If the wall studs are 2 x 4 I believe you can install a R-19 (anything higher will be to thick).

If you want more thermal resistance you can tack 2 x 2's to the existing wall framing to deepen the wall bays.

There's not a lot you can do regarding the concrete part of the wall without major remodeling. Although if the studs are flush with the concrete wall once the insulation is installed in the stud bays you can than cover the wood framing AND the concrete with rigid insulation board. This would give some thermal resistance to the concrete and add more to the stud wall.

As long as the vapor barrier on the rolled insulation is facing the inside of the room and stapled to the stud edge with no gaps moisture shouldn't be a problem.

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    R30 in 2x4 cavities? Won't be R30 even if you can stuff it in. An 8 or 9 inch thick batt crammed into 3.5 inches lacks the air spaces that make it an R-30 batt when installed as intended.
    – Ecnerwal
    Feb 9 at 1:19
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    I think the best he can do with batt-type insulation in a 2x4 cavity is R-13, with something like Rockwool.
    – SteveSh
    Feb 9 at 1:37
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    I believe in our region if the studs are 2x4 then R-13 to R-15 is good enough.
    – Mayur
    Feb 9 at 3:42
  • @Mayur- yes it should be R-19 max for 2 x 4 walls. R-30 is max for rafters.
    – ojait
    Feb 12 at 16:51
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I have decided to remove drywall from the wall as well as ceiling. I will use the combination of foam board and batt insulation.

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  • Since you have all the walls down you should get an estimate for spray foam. It will be more expensive but also best quality
    – Matthew
    Feb 25 at 19:31

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