Messages and Online Forum Q&A

Re: Expansive Soil and Foundation Settling

From: info@builderswebsource.com
Category: Foundations and Basements
Remote Name: 63.198.181.43
Date: 09 Aug 2001
Time: 12:37 AM

Comments

San Diego is known for either sandy soils (near the coast) or heavy clay. Clay soils are notoriously expansive, requiring special consideration when building a home.

Your assessment is probably accurate: your home is likely built on clay soil which expands when wet and shrinks when dry. This is causing your addition to settle, resulting in cracks and other visible structural changes.

Normally, when building a home on clay, the use of pier and grade beam foundations is common. Piers are drilled into competent bearing strata, bypassing the expansive clay which is often several feet deep.

However, in the case of older homes, or homes with additions such as yours, your choices are more limited. Drilling piers is not generally cost-effective on a retrofit basis.

Therefore, your best bet is to stabilize the soil moisture levels around the foundation. Automatic hydration systems are available for exactly this application.

However, there is a downside to this approach. First, it can use a fair amount of water depending on your soil conditions. Second, it can create moisture problems under your house resulting in other issues. Third, it can attract tree roots to grow more aggressively towards the foundation, depending on the location of existing vegetation.

Alternatively, you can just learn to live with the condition (which is what most people do) so long as it's not creating a significant structural impact on the home.

There are some other methods of stabilizing the foundation, such as using a permajack system driven into bedrock. But these solutions are often costly and are not always effective against soil expansion, which can literally lift up a home.

Addition information on expansive soils and foundations is available in our online chapter on Foundations in Building a Dream at:

http://www.builderswebsource.com/book/foundations.htm

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