Stem-Wall-to-Slab Connection
Hi all, building a new house in Florida and I’m driving myself crazy with the stem wall to slab connection. ICF construction, ICF stem wall because it’s easier for me to do myself, and sandy soils. I’m raising the slab up about 3′ just to be safe from flooding or else I would just do a simple slab on grade which is what I am familiar with from past builds.
I’ve attached a PDF of different options for an ICF stem wall to slab connection or non connection. I see pros and cons to each, but wanted to get some expert advice.
Floating slab – I worry about the interior bearing walls settling at a different rate in the house, but thinking of this for garage floor which is at a lower elevation. It would seem there shouldn’t be much capacity to settle though with 32″ of backfill if it is well compacted. With that pressure all being driven down, I got thinking of the possibility of the footers trying to move laterally, so I thought of the next idea (I’m guessing continuous steel around the corners prevents this, but like I said, I’ve been thinking too much).
Doweled slab – I like the idea of tying the slab into the wall with steel to prevent any movement of the stem wall laterally, but I worry about creating pressure points and cracking concrete in the wall or slab.
Full pour over or 2-3″ notch – The notch method is how it is typically done around here when I see block stem walls built (4″ notch) and is the way I am leaning, possibly with a rebar or wire mesh grid.
As always, thanks for the advice.
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The ICF manufacturers I'm familiar with have a block with a brick ledge built in, which I've used to support a slab from sinking. If the sub-slab work is done properly it shouldn't settle, but if it did settle it would be hard to fix, so I think it's a good idea to have a second line of defense. That said, whether pins or a shelf, if there is serious subsidence mid-slab, it's going to be a problem in any case.
Thanks Michael, I agree that the fill is critical. It does seem like there's a little bit of added protection with the shelf for little cost. I'll have to take a look at the brickledge forms, that might be a nice solution.
The way we do it around here...
No bearing wall should be sitting on a non structural slab. All bearing should be directed to the exterior walls, or to interior walls that have footings.
Your non structural slab should actually be independent of your stem walls, and instead of designing an attachment point there should be a bond-break to ensure they can move independently.
The soil will create lateral force pushing your walls inward, and the slab will resist these forces.