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Community and Q&A

Attached Garage Conversion

jack_of_some | Posted in General Questions on

Hi Everyone-

Upstate NY zone 6.

Pandemic requirements: New puppy . Check
Sour dough mastery. Check.   Go crazy with the kids , wife , dog in our 1000 sq ft ranch. Check.

Our plan is to turn our attached garage into a heated living room.  I already had a small pole barn built for all our stuff and moved the garage door over and framed in the old garage door opening.

The garage walls are 2×4 with batt insulation.  I would like to bring this renovation close to stretch energy codes and achieve a wall Rvalue above 20.

Can I safely build a 2nd stud wall inside the exterior walls and insulate the whole cavity with batts or cellulose?

I really don’t want to take the siding off and insulate from the outside with foam boards if at all possible .

But some of the articles I have read about double wall construction and Cold Sheathing have me worried I’m going to turn my OSB to oatmeal if I simply overinsulate the space.

Is this truly a risky way to build?  What , if anything, can I do to minimize this risk outside of wrapping the exterior in a coffee cup?

thanks you!

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  1. brian_wiley | | #1

    Hi Jack,

    Definitely feeling you on the space crunch. I'm in a similar boat and considering a similar conversion, albeit in zone 5.

    What type of siding do you have on the exterior? And, what is the roof and roof insulation situation? Any photos you have of the interior of the garage would be super helpful, too.


    1. jack_of_some | | #3

      Hi Brian- it’s vinyl siding outside with Tyvex and OSB. The roof is engineered trusses with batt insulation that is pretty minimal. I plan to add to this.

      I plan to demo all the wall drywall and build the 2nd stud wall.

  2. Expert Member
    NICK KEENAN | | #2

    Moisture tends to move from warm to cold and from moist to dry. In Zone 6 most of the year the interior is going to be warmer and moister than the exterior. You want a vapor barrier on the interior to keep that interior moisture out of the wall assembly and a wall that is able to dry to the exterior so that any moisture that does get into the wall has someplace to go. I can't tell from the picture what your exterior is but if it's anything at all permeable you should have plenty of vapor drive to keep the wall dry.

    The tricky part about garage conversions is they often weren't really built to be insulated. The walls aren't that bad, it's the floor, ceiling, windows and doors that give issues. Particularly where the walls meet the ceiling and floor. In your climate you really want to be well air-sealed in addition to being insulated.

  3. walta100 | | #4

    I like your goal but I have to ask is it really worth it going from the current R13 wall to your R20?

    From a dollars and cents point of view no one is likely to live long enough to recover the cost of this upgrade in energy savings.

    From a green point of view this upgrade will put a lot of stuff in the land fill for very little energy savings.

    From a usability point of view the double walls eat up lots of the floor space in the new room.

    Will you be adding some windows to the new room?
    What is the plan to heat the new space?

    Is all the wood in contact with the concrete pressure treated?

    It is hard to tell from the photos but the new framing looks odd to me the more I look the less I think it is acquit.

    It seems to me you need the 2x4 to run from the bottom plate to the header in a single piece.

    It seems to me you need all the seams in the sheeting to land over framing members.


    1. jack_of_some | | #6

      Astute observation Walter. There is a large window going there and that wonky framing is just temporary to hold my sheathing scraps covering the opening.
      As for your existential question… I agree that “maybe what is the point of super insulating this space while the rest of the house remains what it isi” .Truth be told , my local AHJ adopted the stretch energy code about 8 weeks ago and if I pull this permit I have to build to that level… quite lofty. My gut is with you. Keep the R13 walls for what they are and don’t landfill or burn more oil for new product.

      As for the other specs. Yes, PT sill all the way around the masonry “wall”. Yes. We are adding (2) 4x4 windows on the south wall. (1) 5’ x 8’ DH / picture/picture on the north wall and on entry door on the north wall. We are going to add a wood stove as well as tie into our FHA duct system

  4. jack_of_some | | #5

    Hi Contrarian-

    Thanks for your advice.

    The exterior is vinyl siding , Tyvex and OSB. The zip sheathing is only where I filled the garage door.

    The existing insulation is faced fiberglass batts, and I’m proposing to add a second layer of faced batts. I understand that the Kraft paper is a vapor retarder not an out and out vapor barrier.

    The concrete slab I can only guess is not insulated. I am going on o add 2” of EPS. Then tap on 2x4 sleepers into the slab and infill with 1” EPS. Put advantech over the sleepers. I am getting new fiberglass windows and doors.


  5. walta100 | | #7

    I am glad that framing is temporary.

    What is your plan for the sloped floor, as is things will roll down hill to the old door.

    My guess is the old walls would be grandfathered so long as you can avoid removing the drywall.


    1. jack_of_some | | #8

      You are good . Making a jig and ripping 2x4 sleepers with my worm drive. It’s a 2” delta across 24’ so I’ll be left with about 1.25” of sleeper on the high side…. I’ll need long concrete fasteners on the low side to go through the 3 inches of sleeper and 2 inches of foam

      One would think this could be grandfathered ( when I spoke to he AHJ , he didn’t seem so inclined.

  6. Expert Member
    NICK KEENAN | | #9

    I'd cut the sleeper to a half inch on the high side. That way you can fasten them to the concrete with relatively normal fasteners. Then attach the foam to the sleeper, you probably only need a half inch of purchase in the wood to hold the foam down.

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