Cracked Foundations, Adobe Clay Soils and Water in Silicon Valley

In Santa Clara County, as in much of California, we have adobe clay soil and it’s expansive.  That is, when the dirt gets wet, it expands, and when it dries out, it contracts. Hence it’s sometimes referred to as “shrink-swell” soils.  (Every state in the union has areas with this problem – a color-coded map on shows areas with more and less expansive soils.)

Why is expansive soil an issue for homeowners and would-be homeowners in Silicon Valley?

The trouble is that the expanding and contracting soil is far stronger than concrete and the foundations upon which a home sits. A well written and illustrated six page paper can be found online explaining the mechanics involved for those interested in more detail on the hows and whys of expansive soils. (It states that the ground can life as much as 5,500 pounds per square inch!)

What I’d like to focus on here is mitigating the risks and preventing the problems associated with expansive soils.

The trouble is not so much that the soil is wet or dry.  The problem is in the back and forth, the movement. When the soil is kept at an even amount of moisture, it does not expand and contract.

Obviously, rain is seasonal and we cannot control all moisture on or near the house. We can, though, work to move water away from the house and away from the foundation.

Keep rain away from foundations on adobe clay soil!

Winter storms can bring an enormous amount of water onto a home’s roof, and when it channels down gutters and downspouts, there can be a large amount of water exiting in just a few places.  Where does that water go?


downspout no extender near foundation