The most common cause is undoubtedly a result of differential soil movement. In Texas many homes are located on expansive clay soils. These soils respond in a like manner to a sponge, increasing in volume with moisture gains while shrinking with moisture loss, about 30% differential is not uncommon. As long as all soils supporting the foundation experience the same volume changes, problems may not develop. However, when a portion of these soils moves differentially to those under the rest of the foundation, distress can develop in the structure.
The key to minimizing foundation movement is to maintain as consistent moisture content in underlying soils as is possible, however, soil behavior can be aggravated by climatic conditions or from excess moisture due to plumbing leaks or drainage problems. These conditions, along with tree root drying effects are some of the issues that can cause excessive foundation movement.
Regular changes in the soil will expose the foundation to continual movement if not prevented. As this movement intensifies, cracking will initially develop in rigid surfaces such as brick and sheetrock, followed by cracking of the foundation, uneven floors and doors. Continual movement can seriously damage homes and result in major reduced property values.