If you notice that the floors of your house are sagging it is a good indication that support structure is sinking or worse, broken. First inspect all of the support beams and posts where they meet the ground. Be suspicious of wood posts set on dirt floors or wood posts with concrete poured around the post bases. As the posts slowly rot and melt into the floor, the house settles accordingly, bottom to top. As a test, firmly push a metal probe or screwdriver into the post at the floor line. If this area is mushy, punky, or rotten, you may have found your problem. In the photo above we see that the previous home owner tried to remedy the issue by using a cinder block and shims, a temporary fix at best because cinder blocks are not designed to take a load such as this and will eventually break.