Suitability of Soils for Buildings with Basements

A building site needs to have soil that will support the weight of the structure without undue settling. The soil should be deep enough to permit excavation for a basement without major rock blasting and removal as well as permitting the reshaping of the area for landscaping. The soil should be deep enough to grow grass, trees, and garden plants.

Shrink-swell of the soil relates to the percent of volume change during wetting and drying. Table 3 shows shrink-swell ratings and values for percent volume changes. Soils whose volume changes by more than nine percent will affect the stability of basement walls, the foundation, patio, sidewalks, and concrete floors anchored to the ground.

Both external and internal soil drainage are important factors. A tendency toward shallow ponding is considered a limitation and occasional flooding is a major limitation. Internal drainage influences the weight the soil can support, the likelihood of wet basements, and the suitability of the soil for growing trees and shrubs. Evidence of water in the soil profile will be determined by identifying the presence of redox features within the upper 40 inches of the soil profile.

The properties listed in Table 4 determine whether limitations occur for houses with basements. The properties listed are not inclusive for arriving at an overall evaluation as to the suitability of a building site for houses with basements.