I live in New England, and am having my current garage renovated into more heated living space.

There is a floor with 2x8 joists being built about 2 feet above the garage slab, and flush with the top of the garage foundation wall.

When complete, the space between the new floor and the slab will not be ventilated.

Should I have those joists insulated?

  • 1
    It sounds like there would be about 18" between the bottoms of the joists and the top surface of the slab. To have a large volume like that not ventilated does not sound good. Leaving aside the moisture question, what about radon buildup? Will the space be accessible through a trap door in the floor? Will you put a moisture barrier on top of the slab? As for your question, surely you will have to insulate between the joists. What kind of heating will you have? – Jim Stewart Jun 5 '18 at 8:47
  • Without a vapor barrier on top of or under the sub-floor water vapor generated in the living space would penetrate the floor and into the joists and build up over time. And water vapor or liquid water could seep into the crawl space and build up over time. This will lead to rotting of the joists and the subfloor. I think you must ventilate this space. What is the soil type under the garage slab? Is this a one-car or a two car garage? – Jim Stewart Jun 5 '18 at 15:44
  • 1
    Just spoke with the contractor and we will be adding ventilation, and insulating, so all should be good. – AgmLauncher Jun 5 '18 at 16:46

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