Inadequate drainage of surface water, whether from rain or irrigation, often leads to saturation of the subgrade soil, the layer beneath your home. This is a prime factor behind foundation problems in Southern California. This inadequate drainage can occur when the topography is flat, slopes towards the house, the volume of irrigation is excessively high, or torrential rains create ponding conditions. In some cases, water may have no escape route, resembling a 'bathtub scenario', or the drains could be blocked.

Particularly problematic are situations where adjacent yards or planter areas are flat or sloping towards the house. This can lead to soil adjacent to the foundation becoming saturated due to inadequate surface drainage during irrigation, past heavy rains, or excessive hose use along the backyard wall.

One commonly encountered scenario is rain gutters that drain directly adjacent to the foundation, often into a planter, which then creates pooling. Ensuring proper drainage is crucial to keep water away from perimeter foundations and prevent foundation movement. As water seeps through the topsoil, it can saturate the subgrade soil under the foundation, rendering the soil under the foundation more compressible and potentially problematic.