Floating basement walls
BILL WICHERS
| Posted in General Questions on
I saw this “floating wall” in a basement in Aurora, Colorado, which is a bit southeast of Denver. Does anyone know the reasons behind this type of basement wall construction? I haven’t seen this before. I’m told it’s to deal with slab movement, but movement like that I’d think would also mess with the foundation itself, I’m not sure what the point would be. In my usual area, basement walls are built directly on the slab.
This “floating” wall is suspended from the ceiling and has something of a double bottom plate with a pin holding the upper “bottom” plate but allowing for vertical movement.
Bill
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Replies
Bill,
Without knowing more it seems like an ingenious response to problem the doesn't exist.
After some more reading, apparently the areas around Denver tend to have a bentonite containing soil that expands with moisture content, causing heaving issues. Strange, but interesting, stuff. Looks like the floating wall framing is a code requirement here.
Bill
There is probably some really interesting detailing that has t0 go along with that. Things like expansion couplings on plumbing, how you handle internal point-loads, and God knows how you deal with the drywall and baseboard trim.
I don't know much about expansive soils, but the walls seem to assume that only the slab will move, not the foundation. Surely it would make more sense to design a foundation that would either stay put or all move at once?
Apparently the foundations in these cases are built on piers instead of footings. I’d still think that there would be a tendency for things to move independently and cause problems, unless the piers are going really deep or even to bedrock, commercial style.
Bill
My driveway slab on clay will move up and down 1-2 inches depending on soil moisture as well as seasonally with temps but my house and basement slab don't do that dance. Seems like if you had good moisture control, the soil under a basement slab would't vary enough in moisture content to expand that much.
But, yes, of all the clays, bentonite is actually used to seal ponds and dams because it expands so much.
Replacing the sub-slab fill with something non-expansive makes more sense to me than floating the walls, but maybe there is something more in play?