Slab Foundations and Water

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All of Central Texas is in a predominate area for expansive clay soils. These expansive soils act like a sponge. As they absorb water they swell and as they lose water they shrink. Soils tend to dry out (and shrink) during the summer and to absorb water (and swell) during the winter and spring.  As this occurs your house and foundation will move up and down. So long as the foundation movement is not great enough to damage the house and/or foundation, it is not a problem.

By keeping the moisture content of the soil under the foundation constant, foundation movement can often be minimized or even stopped. Please note that this is only a simple foundation preventive maintenance recommendation.  Should you be concerned about the possibility of future movement or potential for movement or structural damage then a licensed structural engineer should be consulted for further evaluation and recommendations. 

The goal of a foundation watering program is to maintain a constant level of moisture in the soil under the house and foundation. The best way to water a foundation is to install a buried foundation watering system. If you do not want to go to the expense of installing a buried watering system, soaker hoses will provide you with many of the same benefits. The best way to use a soaker hose is to bury a soaker hose three inches deep, one foot from the edge of your foundation. Placing the hose a short distance from the foundation allows the water to soak into the soil evenly.

The hose should not be placed against the foundation. When soil has dried and cracked, water can travel along the cracks for several feet in all directions. If the soil around your foundation is dried and cracked, then water placed next to the foundation will run through the cracks and accumulate at the bottom of the grade beam (the thick portion of the foundation that is under the exterior walls). In some cases, an accumulation of water in the soil at the base of a foundation can cause the soil to loose some of its load bearing capacity. If the soil loses enough load bearing capacity, the house will sink into the ground.

Obviously, it is necessary to water more during hot, dry weather and less during cold, damp weather. The amount of water required to keep a foundation stable during the summer can be surprisingly large. A single large tree can remove as much as 150 gallons of water, or almost 20 cubic feet of water, from the soil each day. Shrubs and other plants can also remove large quantities of water. During persistent hot dry weather, it may be necessary to water a foundation daily. Watering should supply enough water to keep the moisture content in the soil under the foundation constant. If the amount of water applied is only enough to keep the surface damp, the watering program will not work. Obviously, the homeowner is the only one who can weight the benefits of controlling foundation movement versus the increased size of the water bill.

Some notes about Texas slab foundations

Slab foundations in the Greater Central Texas Area are designed for some movement. They are sometimes referred to as “floating slabs”. The use of rebar and post tension cables allows for minimal movement without causing serious damage to the foundation or the structure of the home.

Many times you will notice cracks along the corners of a home. These are very common and are more cosmetic in nature and do not affect the performance of the foundation.  Common expansion and contraction of materials places undue stress at the corners of the home and the result is this minor chipping or cracking of the mortar coating over the foundation wall.

Many years of experience has taught me that if you consult with a foundation repair company about the movement of your home’s foundation, you will more than likely be given an estimate of repairs which could easily run into the thousands of dollars. Get a second opinion!

Some repair companies may recommend the addition of foundation piers or supports. These act as an extra support level for the foundation to help prevent future movement.  And they are sometimes warranted.  My advice is to first consult with a State Licensed Structural Engineer before moving forward with ANY foundation repairs. You may save yourself thousands of dollars in repairs that are not needed. Often, a simple watering plan may be all that is needed to correct your foundation problems.