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Cold Room under heated front entrance

nipperkin | Posted in General Questions on

Hoping to get some advice on the best way to finish a new cold room that will be underneath a small somewhat heated area that is an addition to an existing home.

The new cold room will be a new block foundation connected to the existing basement with a door cut out (3 new walls). On top of the foundation will be a new framed front entrance addition that will act as a vestibule. The entrance will be insulated and have a duct for heating, although it will likely be cooler then the main part of the house. We decided that a traditional concrete ceiling to the cold cellar didn’t make sense due to the extra structure required and the fact it would likely make the front entrance above even cooler (we live in zone 6). The roof of the cold cellar will be about 3 feet above grade and the floor will be about 6 feet below grade.

We are thinking of either spray foaming the ceiling, headers, etc and/or  using dense board or concrete board to create an additional barrier between the floor above. Possibly also adding rigid insulation on the above grade walls as well along with a vent to help control humidity. Any thoughts  on this plan or potential moisture or mould issues we should be concerned about?

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  1. Expert Member
    NICK KEENAN | | #1

    Will this room be refrigerated or just unheated?

  2. nipperkin | | #2

    The room will be unheated and unfinished with a sealed exterior grade door separating it from the main basement.

  3. Expert Member
    NICK KEENAN | | #3

    Is your desire to have it be cold in the winter and hot in the summer, or a cool temperature year-round?

  4. nipperkin | | #4

    The intention is for it to be a cold cellar (as best as possible) so cool all year round.

  5. Expert Member
    NICK KEENAN | | #5

    Find out what your year-round average temperature is. (You can get it by getting the monthly average high and low and averaging all 24 numbers). When you dig down far enough into the soil that the temperature is stable, that's what it will be. That's the temperature your cold cellar will be. Before embarking on this adventure make sure that temperature is acceptable to you, in zone 6 it's probably high forties or low fifties.

    To maintain a stable temperature you need about R-40 of insulation on the exterior.

    Humidity is going to be a problem. In the summer your dew point will probably be above the temperature of the cold cellar and any air that gets in will cause condensation. There really isn't any way for moisture to get out in the summer, the vapor drive is all inward, so once that moisture gets in there's no getting rid of it and it will be damp all summer. In the winter when the dew point is below the interior temperature you can dry things out by ventilating but there are going to be long periods where that isn't possible. You want to make the whole thing out of moisture impervious materials, but in moisture mold will grow on impervious surfaces like concrete, plastic, steel and even glass.

    You could do some combination of dehumidifying and cooling, but that's getting more complicated.

  6. nipperkin | | #6

    Thank you DCContrarian

    We realize we are not going to get a perfect solution here given the constraints we are working with. Therefore we are looking to strike the best balance we can. We are in zone 6 so it will be humid in the summer and cold in the winter.

    To clarify, when you say R-40 on the exterior do you mean between the main basement and the cold room or inside the cold rooms walls that face the exterior?

    I agree, humidity will be our biggest challenge. This seems to be a common problem that all cold cellars need to deal with and there aren't a lot of silver bullets for a situation that has some constraints like ours. It sounds like the best we can do is make try and make it as vapour impermeable as possible. With the caveat that we may have moisture to deal with at certain times of the year. I was originally thinking of using spray foam on the headers, etc to cover the vapour impermeable part. However, I'm not questioning if that makes sense as it's not a solution that can be undone easily if we need to make modifications and adjustments. Thoughts?

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