Building on fill dirt is not advisable, as the dirt takes many years to settle and causes extensive damage to the building, such as shifting of the foundation, which causes cracks in the walls. Building on compacted gravel as fill is advised as an effective alternative to dirt fill.
Building on expansive soil, like clay, is also not advisable. Clay will compact when it is dry and expand when wet, which can cause foundation problems. Stronger and larger footings are needed when building on clay.Learn more about Building Materials