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Community and Q&A

Attached garage with steps leading into basement

Dirk Denzin | Posted in General Questions on

We are building in SE Wisconsin. Currently just figuring out floor plan, in a rough design stage. Main level of house approx 1 ft above grade to approx 4 ft above grade on south side. Basement of house to be partially finished on south 1/2 of house. Attached garage on north side of house. Garage to be on same level as main floor of house. My questions deal with having a stairway in the garage leading to the basement level.

I would like to insulate the exterior of the basement walls. My reasoning is that the basement is going to only be partially finished and I want to keep it dry and warm as possible. I want to stop moisture and cold from getting into the concrete as much as possible from the outside rather than putting up a barrier inside.

So I am concerned on how to deal with the stairs from the garage, an unconditioned space to the basement, a conditioned space.

How is this situation treated as far as footings below the frost line? I assume that the bottom of the stairwell Or at the very least the basement floor has to have footings down an addition depth because the stairwell floor is now effectively “ground level”.

If I put either rigid foam or mineral wool on outside of basement walls do I insulate to the door opening on the bottom of the stairwell then pour concrete for stairwell up to the insulation effectively sandwiching insulation between basement wall and stairwell walls and floor?

Would it help to not insulate outside of stairwell walls below grade and build walls that could be insulated above garage floor adding an additional door on the top of the stairway. This would add a buffer area that would be “heated” from the ground in the stairwell and trapped there by the insulated walls above the garage floor.
Thanks for all responses.

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  1. GBA Editor
    Martin Holladay | | #1

    This isn't much different from a stairway under a bulkhead. At the base of the stairs, you'll install an insulated exterior door.

    I thin that it's unlikely that frost will get under the walls that line the stairway. That said, it wouldn't hurt for your excavation contractor and concrete contractor to place the footings for the walls on either side of your stairway as deep as local soil conditions allow.

  2. Dirk Denzin | | #2

    Martin as I mentioned in first sentence I'm in SE Wisconsin.
    As far as frost getting under the walls that line the stairway, why wouldn't it? its in an unheated area exposed to below zero temps. The stairs and the walls in the stairwell are exposed.
    One of my questions was to make a "bulkhead" in the garage to add a buffer area and then protect the walls and floor from freezing temps. By your saying this is the the same as a bulkhead setup are you then saying that the additional walls and insulation is a good solution to reduce heat loss thru basement door and protect the stairwell from freezing temps? Or even without the additional walls and insulation do you think that just being in a garage makes the difference needed to protect the stairwell from freezing temps?

  3. GBA Editor
    Martin Holladay | | #3

    Thanks for pointing out your location again; sorry I missed it. I'm interested in hearing from other readers.

    There are several reasons why I think that frost won't penetrate deeply in this region. One is that the interior of your garage will be warmer than the exterior air, especially if you keep your garage door closed. Another reason is that your basement will be leaking heat, warming the nearby soil. A third reason is that the base of your stairway walls will be 6 or 7 feet below grade.

    All of that said, deep footings will be safer than shallow footings.

  4. Expert Member
    Malcolm Taylor | | #4

    The situation is very similar to exterior stairs leading to basements. The standard detail is that wherever you do not have enough cover over the footing to prevent freezing, you place foam horizontally on the top of the footing extending two feet out from the wall. Whether, as Martin says, it's necessary inside a garage is your call.
    If you are still at the design stage you might try and eliminate all the extra work by moving the stair out of the garage and into the basement.

  5. Rick Van Handel | | #5

    Don't worry. It will never freeze at that depth. Think about it this way, manholes and storm water catch basins are concrete structures back filled on outside only. The interiors are fully exposed to freezing air with no heat sources at all. Seldom are there any frost problems, even when the structures are too shallow. If you have foam underneath your basement floor you will have additional protection

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