GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Attached Garage and Conditioned Room Temp Fluctuations

NotslarJ | Posted in General Questions on

I’m in a newly constructed house by a decent tract builder near Atlanta (zone 3). My master bedroom is at the back of the house on the second floor. In front of our bedroom is our master closet which abuts the uninsulated garage attic (that wall is insulated and sheathed with OSB on the garage side). We also have a large storage area in the garage that goes under a portion of our closet and bedroom (there is insulation in the joist space between the garage ceiling and our bedroom/closet floor). Prior to building, I was concerned about temperature issues with my room being partly over the garage but was assured that it would be sealed and insulated well and wouldn’t be a problem. It’s a problem, but one the builder won’t take care of (because on the really mild day they checked, there was less than a four-degree difference between rooms upstairs). So I’m looking at various ways I can improve my room’s comfort and reduce the temperature swings. I believe the most influential changes I can make at a reasonable cost are to insulate the garage to some extent since that affects our closet wall and our floor. I’ve insulated the 2-wide garage door with a radiant barrier bubble wrap style insulation. So far, I don’t think that will do much because the ceiling in the garage isn’t insulated. So I’ve had a few thoughts and I’m not totally sure which way to go. I’ve thought about using the radiant barrier bubble wrap on the underside of the garage rafters to reduce the summer heat gain in the garage (and to a lesser extent keep in some heat in the winter). I’ve also thought about using that radiant barrier bubble wrap or some other type of insulation on the attic side of our closet wall, but that won’t help with the floor/garage ceiling. Obviously, I could also insulate the ceiling with batts, but I feel like that will help more in our short winter than in our long, hot, summer.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. JC72 | | #1

    The problem with garage doors is that you can't air-seal them so it really doesn't matter how much extra insulation you add to the door itself.

    [We also have a large storage area in the garage that goes under a portion of our closet and bedroom (there is insulation in the joist space between the garage ceiling and our bedroom/closet floor). ]

    Q: With regards to this ceiling. Do you remember if the builder installed blocking within the I-Joist at the transition from the garage ceiling to the storage space ceiling?

    I also live in Atlanta and although it has been awhile I rarely if ever see a builder air seal this transition or do it well. Especially when they use I-joists which is so common. So it's possible that you have cold air moving from the garage along the joist towards the floor of the closet. Usually they just wedge batt insulation in that space and it could either be an inadequate amount or not against the subfloor of your closet..

  2. NotslarJ | | #2

    I understand what you're saying about garage doors, but I figure for not a whole lot of money, some insulation has got to be better than literally just sheets of steel covering the huge hole in the wall, and, this door actually seems to be sealed about as well as a garage door can be.

    The joists do not go into the garage attic area, so yes, they're sealed on that end by the OSB sheathing. How well they're sealed, I have no idea. I poked a few holes in the ceiling to verify there is insulation, but the holes I poked were too small to really get an idea of how much insulation there is.

    1. JC72 | | #5

      Does this storage closet/room have an uninsulated exterior wall? Also It just seems odd that a builder would insulate the wall which separates a storage room and the garage.

  3. walta100 | | #3

    My wild guess is that a 4° room to room differential is too large a change to be all or mostly about insulation. I am betting there is a huge air leak somewhere and you can fell where the cold air is getting in to replace the missing air. Do you have a fire place, a wood stove or maybe a huge range hood?

    Has the home been tested with a blower door?
    IR photography is a very useful tool.

    Radiant barrier bubble wrap is not insulation it is a marking scam and is next to useless.


  4. NotslarJ | | #4

    We have a fireplace insert downstairs on the other side of the home. No strange temperature differences around there. We have a range hood under our bedroom which is vented through that garage attic space to the outside. No apparent gaps in the duct or problems with the outside vent flap. I have not been able to feel any specific cold air, just cold space (the closet).

    We have not had any tests done because it looks like I'll have trouble getting the builder to do anything about it so I'm trying to think this through before pulling the trigger on anything. I've thought about getting an IR phone attachment to do some checking myself...but that's not cheap.

  5. user-723121 | | #6

    Describe the heating system. A cold room can be caused by a number of factors.

    Remote from mechanical room
    Large percentage of exterior wall compared to rest of house
    High level of air leakage
    Inadequate insulation

    I have built rooms over garages that are far away from the heat source but get heat when the the thermostat calls for heat in the main portion of the house. Those rooms are highly insulated, very airtight and are toasty warm in our MN winters.

  6. walta100 | | #7

    Jon you are missing my point. A huge amount of warm air will be exiting your house when a fire is burning all that air will be replace with air from outdoor. The outdoor air will find a way in or the fireplace will back up and the house will fill with smoke. The air will use the path of least resistance that could be close to the fire place or on the other end of the house and if most of the air is entering in one room that room will get very cold.


  7. NotslarJ | | #8

    John, I don't think it's strange the builder would insulate the wall between my bedroom closet and my uninsulated garage. My temperature issues would be much worse without that insulation. Two walls of this closet are outside walls and are insulated with R-13. Two walls are interior and abut my bedroom and laundry room.

    Walta, I understand your point. It's cold whether I'm using the fireplace or not. It's cold whether I'm running the range hood or not.

    Doug, we have a single air conditioner and a single gas furnace split with an upstairs and downstairs thermostat. The air handler is in the attic. The ductwork is all properly insulated. Our bedroom and closet are about half the house width from the furnace, but compared to the furnace being in the basement, it's relatively close. I know part of the problem is the central air return and the builder's reliance on door undercuts for return air, but the temperature difference exists regardless of whether the air/heat is running or not. That leaves air leakage or insulation. Like in my original post, I know there's insulation in the floor joist space above the garage and my builder says that's R-19 with R-13 in the walls. The room does have two outside walls with the closet making a third "outside" wall, and the floor being "outside" as well. So the gist of my problem is that the builder may have technically done everything ok, but not well. My room is hot/cold at least in part due to sharing a wall and floor with the unconditioned garage space. Short of tearing out the walls to better insulate, can I do anything in the garage to make my closet wall and bedroom floor less "outside"?

    I plan to attempt some air leakage checking myself, and maybe order a thermal imaging attachment for my phone (which I'll probably return).

    1. JC72 | | #9

      [John, I don't think it's strange the builder would insulate the wall between my bedroom closet and my uninsulated garage. ]

      - I'm talking about the storage room in your garage (underneath the Master Bdrm closet). I thought you implied that the builder air-sealed the garage from the house with OSB sheathing on the garage side of the wall. That would be hard to do unless the joists were parallel to that wall.

      Perhaps a drawing?

  8. user-723121 | | #10


    Any chance of adding another supply to this room? In my part of the world, bedrooms will have a return to the furnace which now has to have a hard duct (no panning). If I am understanding you correctly, part of the bedroom floor is over the garage. If the subfloor (T&G) is glued to the floor joists this will provide an adequate air barrier. More insulation may help but I think it is more an air leakage problem and inadequate heating and cooling volume from the furnace. The heat loss and gain in this room is greater than the rest of the house where your thermostats are located. Rim joist areas are often given short shift for air sealing and insulation, you may want to check this.

    1. NotslarJ | | #13

      Based on how cold this closet is and it's not yet below freezing at night, I might be able to get the builder to address some airflow issues. Another supply and return would definitely be helpful.

  9. user-2310254 | | #11

    Jon R,

    I am in Atlanta as well. Before we moved into our townhouse, I had concerns about the garage being connected to the conditioned part of the house. There was fiberglass stuffed in the ceiling and walls, but I had heard some comments that second-story floors tended to be colder than the rest of the house.

    To address my concern, I had a contractor pull down some of the garage drywall (ceiling and divider wall between garage and living space). I then had open cell foam sprayed in these areas to air seal and insulate. This retrofit achieved most of my goals, but I did notice that my office, which is next to the garage, was staying a few degrees cooler than the rest of the house. I talked to my HVAC installer, and he thought it was a air supply issue, which he solved the problem by putting an additional supply in the hall and attaching it to a damper that could be controlled from the office. (I close the duct during the cooling season to prevent the office from getting too cold.)

    I agree with you that there are probably some air sealing, insulation, and the HVAC supply issues. Only you can determine if fixing these problems is worthwhile. If it involved a lot of cost and hassle, I'd be tempted to install some supplemental heat in the closet and call it a day.

    1. NotslarJ | | #14

      Steve, thanks. I'm thinking that may be one of my moves in the future, but my income is suffering with the pandemic so I don't want to hire anybody for the time being.

    2. JC72 | | #16

      Didn't you know that cold floors in rooms above garages are feature in Atlanta? Did your builder place the HVAC in a garage closet? If so, did they use a flexible collar to air seal the duct passing through the top of this utility closet or spray some canned foam? I'm just curious.

  10. NotslarJ | | #12

    Here's a super crude drawing of the garage storage, closet, wall interface. Basically, they built the garage, built the room and closet on top, wrapped everything with OSB, then put the rafters up over the garage. The joists run parallel to the storage room and the OSB is placed perpendicular to the ends of the joists.

    1. JC72 | | #15


      I can only think of insufficient insulation between the joists of the closet floor. You could probably rent a borescope from an auto-parts store and then drill a couple of holes in the ceiling of that storage space to see what it looks like.

    2. user-723121 | | #17


      Floors over garages can be warm, even in Minnesota. I have used 16" 2x4 web trusses filled with blown insulation (R-50). The rim joists were 3 layers of R-10 (R-30) Thermax tightly air sealed. The web trusses avoid some of the direct thermal bridging you would get from standard dimension lumber as the conductivity path is much longer due to the triangulation in the web trusses. If you have access to the attic you might check for any bypasses there. A comprehensive air sealing wherever you can in this room will help greatly with comfort. Because of the bedroom location and all of the exterior surfaces this room will need extra insulation, air sealing and conditioning to maintain the thermostat setpoint temperature. Add a supply if you can.

  11. NotslarJ | | #18

    Thanks for your input everyone

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |