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Community and Q&A

Insulating a Partially Underground Concrete Garage

nicow | Posted in Energy Efficiency and Durability on

We are developing a project with a partially underground concrete Garage in Northern Climate Zone 6. The Garage is not unlike a bunker in that it will also have docks plank roof deck with membrane and pavers or landscaping above. We will have an insulated Garage door. While not receiving daily use (weekend cottage), the accumulation of moisture from a vehicle driving through rain or snow to get here will build-up moisture and venting can only do so much with extremely cold air since the concrete will seal the space. A good floor drain to take any melting snow away, possibly a heater are some approaches. Encasing inside and outside in rigid insulation seems to be the best approach – however, we will most likely have exposed portions of sidewall on the sides and at the Garage door side. Both these would not have exterior insulation and there in lies the rub – do we over compensate on the interior if we want exposed concrete to show on the exterior?

Any thoughts on this kind of condition and the best approach to controlling moisture build-up/keeping things dry?

Thank you

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  1. Expert Member
    Michael Maines | | #1

    Nicolaas, unless you want to build with ICFs I would not insulate both the interior and exterior. Choose one. I recommend the interior, since concrete is a resilient exterior on its own. Thermal mass doesn't matter much, despite popular opinion. Exhaust-only ventilation works well in a garage to keep air moving, which dries everything out.

  2. Jon_R | | #2

    In some weather, ventilation will help, in other, it will add condensation - a smart fan that knew the difference would be helpful. Otherwise, a dehumidifier will work in Summer, a little heat will work in Winter. Rust and mold are greater problems when warm, so I'd worry more about Summer.

    Dehumidifier energy use is mostly about air sealing.

  3. nicow | | #3

    Thank you Michael and Jon for your replies. We will most likely build with ICFs for most of the rest of the building, but will have an above grade exposed portion at the Garage where adjacent grade slopes for which we will want exposed concrete.

  4. Jon_R | | #4

    As far as I know, insulation alone won't help the moisture situation. So if you aren't going to heat the garage, then I wouldn't insulate at all.

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