Messages and Online Forum Q&A

Re: Jacking a sagging floor

From: info@builderswebsource.com
Category: Foundations and Basements
Remote Name: 63.198.181.43
Date: 22 Jan 2002
Time: 10:44 PM

Comments

With your confirmation of clay soil in your area, the problem you're having may well be a result of differential settlement due to expansive ground. While only an onsite inspection could confirm this for certain, you have a range of possible paths to follow.

First, proper foundation drainage is critical to ensuring a stable moisture condition under the house. Without good drainage, the under-house soil can expand in the rainy months, and shrink in the dry months. French drains and a closed perimeter roof drainage system can help to mitigate these problems.

During very dry spells, there are some systems that actually increase the moisture around foundation. We tend to shy away from these kinds of remedies for several reasons. One is that they waste water. Two is that the moist foundation isn't necessarily a good thing, and it can lead to premature rot and high indoor humidity. Finally, the moisture invites tree roots to grow under the house, which can further damage foundations.

The best method of stabilizing foundations on clay soils is to use a pier system. Ideally, when the foundation is built, drilled concrete piers are spaced every few feet around the foundation, including interior partitions. The piers go down past the expansive clay soils into a more competent bearing soil, which hold the piers in place due to skin friction. Our home is built this way...and only after we experienced the problems that clay soil can wreak on a foundation.

Of course, this is an expensive proposition on an existing home. Therefore, we do recommend that you hire a reputable geotechnical firm in your area to evaluate your site and make some specific recommendations. Chances are they've done geotechnical reports around your neighborhood and already have a pretty good idea of the soil characteristics.

While intermediate jacking may help temporarily, ultimately the soil will win the battle. Your only long-term solution is to design around the soil conditions and mitigate their impact on the foundation.

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