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Thread: Gap between slab and stem wall
06-18-2011, 06:45 PM #1
Gap between slab and stem wall
I observed a 1/2" gap between a slab floor and the stem wall. It is about 20' long and runs most of the width of the house. You can clearly see the stem wall through the gap. There are no cracks in the stem wall, the walls, the ceiling, or windows. There appears to be some heaving as the slab is about 1/4" above the bottom of the baseboard trim in the center. There are only a few hairline cracks in the slab, although the house is carpeted so only the immediate area was observed. The tile floor in the kitchen along the shared wall is okay. Is this a structural issue or slab shrinkage, or heaving from expansive soil? A contractor friend suggested that the stem wall settled, but I didn't see any visible cracking of the stem wall. We do have expansive soils in Phoenix but this is the first time I've seen the slab raised. Any suggestions are appreciated.
06-18-2011, 07:53 PM #2
Re: Gap between slab and stem wall
Sounds to me that you are describing a floating slab which is not keyed into the top of the stem wall, and as such is allowed to "float" (intentionally or not) on the fill as the fill rises and falls with its moisture content.
I have seen this on houses in South Florida, not caused by expansive soils but caused by simple settlement over time of the fill under the slab. I've seen where the interior walls were hanging from the ceiling joists and the floor and slab had dropped 3 inches. The wood base had been removed and 6 inch tile base installed, then the slab settled another inch or so and I could see the cut nails hanging down through air from the bottom plate of the interior walls, nails that at one time had been driven into the slab at the time of construction.
I noticed the interior walls first, then the exterior walls as I checked for loose tiles to remove for a better look.
In one case my client walked, in another my client took the house with a very large discount off the price - all we do is advise and educate, the client makes the decision of what to do with that information.