We live in a 1930's era wood frame house with a stem wall foundation. Unfortunately, the soil here is very heavy clay a foot or more below the surface. To compound this the builder did not pour a footing below the concrete block stem wall. I have directed water from the roof away from the house to minimize future problems but am faced with some small areas where there are blocks that shift every few years after they have been re-set with concrete. The builder also created long spans (ca. 20') with no intermediate support so there is sagging in many floors and doors that either drag on the floor or do not sit straight in the jamb.
Questions: Is there a DIY way to stabilize the stem walls without having them torn out and repoured the correct way?
What are the best ways to support the sagging floor joists. Independent concrete footings spaced, say, every four feet with a 4x8 running perpendicular to the joist braced on top of the footings with a 4x4 after the floor is jacked up? Any suggestions greatly appreciated.