movement of multiple additions

[unsettled]

Hi-

My house was built in the 1950s on very contractile clay soil, on a slab. Subsequently there were two slab additions, one adjacent to the other. While the original house has a little bit of movement, and a few cracks, these are not as bothersome as the major movement that occurs in the additions. The room floats up and down visible about a half an inch depending on how wet the soil is. I can minimize cracks by flooding the foundation with the soaker hoses in the back, but we are talking a hundred dollars of water a month just for the soaker hoses. The day I turn the hose off my bedroom door starts sticking and within a week or two the bathroom tub is uncaulkable. We had a couple of engineers look at it and one suggested putting in several piers under the corner of the house, but I keep hearing how doing work like this on additions is frequently unsatisfying---one can spend 15K and still have just as much movement as before. I am going to have to do a fair amount of cosmetic work in the house regardless, and really just want something to make it quit moving around so much. What about these soil stabilizers---do they work for something like this? I also wondered whether just digging out the soil from around the corner of the house and replacing it with rocks would make any difference.

Thanks in advance for any suggestions.

[FIXITGUY1971]

With your slab being subject to movement due to moisture changes in the soil some thoughts come to mind. First of all there most likely are some major voids beneath your slab now and I suspect there was no engineered fill material beneath the addition. The first thing I would do is "sound" the floor by tapping several areas with a steel bar or heavy hammer. If there are hollow sections you will be able to hear it. If you find a few I'd suggest you consider having the floors mudjacked or slabjacked. This is the least expensive of all repair methods for leveling your floors.
It is quite possible that the material beneath your floor is the culprit...and not a soil deep soil failure, as your foundation seems to respond quickly to surface moisture changes. Had anyone though of this?

[unsettled]

Interesting. There are quite a few hollow spots, especially under this part of the house; it sounds like a pier and beam foundation. I highly doubt any sort of engineered fill material was used at the time. There was some kind of underpinning done ten or fifteen years ago which could potentially have contributed to creating voids, I suppose. I will look into mudjacking.

No one has suggested the possibility of it being a sub-flooring issue rather than a foundation issue, but it's hard for me to imagine how surface moisture outside would get into the sub-floor, since the slab height extends at least eight inches off the ground. Also, you can see widening of the crack between the original slab and the first addition that has taken place since we moved in.