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Attached garage below grade

Yoni_Green | Posted in General Questions on

Our 1925 house in Zone 5 has a below grade garage that is attached to the house. I have attached a side view of this part of the house. The house has a lot of energy inefficiencies due to this design. 

Should I air seal the gaps under the kitchen floor? If yes, there are some fairly large holes (see pic). How should I seal these holes?

A related question, should I add insulation above the garage roof, including under the kitchen floor? If I do, should I air seal it with spray foam before adding batt insulation?

I appreciate your responses. This forum is one of my favorite places on the internet. 

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  1. walta100 | | #1

    Seems to me the smart move would be to repurpose the space for anything but a car.

    Today’s fire code would require fire rated walls, ceiling and doors for such a space today.

    Two layers of drywall with staggered and taped seams would be a good air barrier


  2. Expert Member


    The two priorities are:

    - Creating a fire separation between the house and garage. This is as simple as using 5/8" drywall on the walls and ceiling.

    - Air-sealing between the garage and the house. Mainly to keep the exhaust out, but it will also improve energy efficiency. I wouldn't worry too much about the holes in the sub-floor above. Insulate the rim joists with foam board, and air-seal them with canned foam. Fill the joist spaces with batts, and use the drywall as your air-barrier.

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