There are other causes. It could be poor building method of the wall, or rot ,borer and whiteant in the wall(s) ?
If its in the foundation itself,
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Is it seasonal ? is it particular wet or dry there ? if so, it will just reverse when weather normalises…
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Is the construction on piers ? so you can just raise and lower joists ?? use a car jack, lift up the joist, adjust the level, drop it back down… of course if the pier is no longer stable, then make it stable first… If you are in an area prone to movement or ground heave, you have a house on piers ? Where the foundations were made from wood, then they can rot away, and need replacement.
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is there ground water flowing ? you might have to first install drainage system to prevent ground water flowing through your foundations.
4.What makes you think the fault is repairable ? If its a slab, its hard to repair. You repair the crack in the foundations at one place, it cracks right next door. A repair is not curing the cause of the cracking… There can be repairs to be made, eg if the ground is rocky, a section of rock could become loose and so require the repair … and a cure of ground water issues ?