By K. M. Kirk, P.E.


Structures build on clay soils are prone to movement, if the moisture in the soil changes. In the Dallas/Fort Worth Metroplex there are two types of houses, houses which have moved and houses which will move. The amount of movement can be minimized with an on going foundation maintenance program. This directive is provided to give the home owner a guide on the care and maintenance of the foundation on which their home rests. Information provided is based upon over 40 years of experience with clay soils.

Clay soils expand when wet and shrink when dry. Some clay soils can expand up to 350% (3- 1/2 times their dry volume), when saturated. This characteristic creates a problem when structures are constructed on these soils.

In areas, such as the D/FW area, the climate changes from very wet to very dry. Since you cannot keep the soil dry, the only alternative is to keep it wet. The most practical method to maintain consistency of the soil is to water the effective

and keep them moist. Soaker hoses are used for this program.

The soil adjacent to the foundation should be not less than 3"; below the brick line (FHA guidelines show 4"; below finished floor) and should slope away from the building. This slope allows surface water to flow away from the foundation. All gutter down spouts should discharge away from the building, not less than 4 feet from the building.

Irrigation sprinklers are placed to provide adequate water for grass and shrubs. They do not, nor are they intended to, provide water to maintain the moisture required to persevere a constant moisture in the soil under the foundation. Soaker hoses should be placed against the foundation and should be on the surface. They should be periodically checked to be sure they are not faulty.. They should be placed around the entire structure as shown below.

soil and the foundation in addition to wetting the soil near the foundation. The farther the soaker hose is from the foundation, the more difficult it is to provide water under the foundation.

Place the soaker hose next to the foundation. Remember water always runs down hill. This will allow the moisture to enter under the foundation along the interface between the

The soil should be kept damp adjacent to the foundation. If it is allowed to dry enough for the soil to “pull away” from the foundation, the resulting crack allows further drying of the underlying soil and can result in the perimeter of the building settling. Check the soil weekly. If it feels dry, turn on the soaker hose. It may take 8 hours or more to saturate the soil if it is allowed to dry too much. If the perimeter of the house has gone down due to drying of the soil, a long term concentration of water may raise the moisture in the underlying soil sufficiently to lift the perimeter. Lifting by injection of water is a proven methodology (University of Texas). If the soil has dried so much that the interior of the house has gone down, it is possible to lift the

interior using water. A Foundation Engineer should be consulted before this is attempted.

Plants which draw large amounts of moisture from the soil, such as Photenia, should not be planted next to the building as they will draw large amounts of moisture from under the foundation. Climbing plants such as Ivy should not be allowed next to a building as they will climb the wall, embedding their roots in the wall. This allows pest infestation and damages the wall, whether wood or brick. Trees should be planted at least their mature height away from buildings to minimize their roots' effect on the building. Plants adjacent to the foundation should not be allowed to grow more than 4' in height. This limits the root intrusion under the foundation.

Remember that a good preventative maintenance program will save you thousands of dollars in repair bills.

epared by: K. M. Kirk, P.E. 1400 Country Lane, Allen, Texas 75002 Ph 972-359-6584

File: Engr/soak-bk.doc