Stem wall minimum thickness- insulated slab detail.
Thow
| Posted in General Questions on
I’m interested in using this insulated slab detail for a project in Idaho. The structural engineer on the project hasn’t seen a stem wall blocked down to 4 1/2″ before. IRC code specifies 6″ nominal concrete thickness. Do you have structural calculations to support this detail?
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Replies
Thow,
I'm in a high seismic zone where structural engineers get a bit uneasy about reducing the width of the stem-walls, and our code requires full width foam between the slab and wall, so sloping the foam doesn't fly.
What I do now is cant the outside of the concrete stem-wall so the plate can overhang the interior face, but the wall effectively is full width.
Interesting alternative option. The structural engineer in this case feels ok with the detail, but was hoping that there was some data to back it up in case it gets flagged by the building department.
Throw,
If the structural engineer is okay, the inspectors will defer to them. At most they may want them to sign off on it.
Another way to look at it, if your code allows a 2x4 wall there, than your 2x6 wall only needs 3.5" of bearing.
Unless you have bare concrete floors, it really doesn't matter.
The floor does not need to sit on a ledge
There is precisely zero load 2 inches from the wall.
Even if you had concrete floors, 1/2 sheetrock, 3/4 baseboard, 3/4 quarter round, gone
And concrete floors are a horrible floor, looks good in the magazines.........
Why is concrete a horrible floor? Polished concrete finished floor seems to be very popular in many of the 'pretty good' type projects discussed on this site
Thow,
Consider moving the exterior foam in. This will allow the stem-wall to be 6" wide at the top, and protect the bottom of the foam.
Malcolm,
I'm puzzling through a similar condition to this in a mudroom remodel on my own house. Question about that sketch you posted:
How do you deal with that concrete lip on the exterior side? Practically, it seems like it's not a big deal since there'd be foam + siding, or foam + rainscreen + siding, so the chances of any water hitting that concrete ledge would be very low. But I'm wondering if you would put metal flashing there, or liquid flash it or something?
Paul,
It depends where the WRB is. If it is on the sheathing behind the foam, then flashing, or at least a layer of peel & stick at the bottom makes sense to divert water outward. If the WRB is outside the foam, then the assumption on pretty much all walls is that water isn't getting further into the assembly, and I think you are safe omitting the flashing.
Not having to protect the bottom of the foam leaves you with a much simpler task, and more options, protecting the bottom of the rain-screen.
Cool, I dig it. Thanks for the explanation.