Many areas have soils which are referred to as expansive or active.
This type of soil generally contains clay minerals which expand and contract depending on their moisture content. Exterior and interior cracks are normal conditions for homes located in active soil areas. Changes in soil moisture content may cause the foundation to uplift during wet periods and deflect downward during dry periods. Foundations built over such soils are expected to undergo these movements without affecting the structural adequacy or the load-carrying capacities of the foundation , floor slab, or structural members. These movements may result in cosmetic deficiencies in the superstructure supported by the foundation and related parts, but does not in itself indicate a structural defect.