Watering Your Foundation during the Drought

By: Fred Willcox
Copyright© 2011
All Rights Reserved

Before you break out the water hose to water the soil supporting your foundation in the Greater Houston area there are at least two things that you should know.

The first is that your house is built on an expansive clay soil.

The second is that your foundation is, in fact, experiencing “settlement” from the lack of support from the clay soil.

To answer the first question, if your house is located south of IH 10 from Highway 6 east to downtown Houston and south of Highway 59 from downtown Houston to Humble, the odds are that you live on an expansive clay. If you live north of those highways, the odds are that your house is supported on a silt or sand soil. If you have naturally growing pine trees the odds are that your house is built on sand or silt soils. The pine trees can be confusing as pine trees will grow wherever they are planted. They will only reseed naturally in sands, silts or gravel.

If your house is located on a sand or a silt type soil, watering your foundation will lubricate the soil particles and can cause the soil to wash out from under your house. Sands and silts are cohesionless soils, meaning that you can’t mold them like dough. The soil is capable of supporting your foundation because of the friction between each individual particle. If you add water to the soil, these frictional bonds are lubricated and the soil can consolidate and lose volume. If this happens, you will be the cause of your foundation problem.

If your house is located on an expansive clay, foundation watering can be a good idea if, and only if, you need it. You need foundation watering only if your foundation is showing signs of “settlement”. This can be tricky to determine. Cracks may be occurring in your walls whether your foundation is “settling” or not. The heat and the dry weather are causing your house to literally shrink. As your framing and siding and your roof get smaller, cracks can develop in these surfaces. These cracks will tend to be vertical, not diagonal. If your foundation is settling, you are more likely to experience diagonal wall cracking, out of square doors and windows and floor slopes.

As the weather is hot and the atmosphere is dry, water is being rapidly absorbed into the atmosphere. Mother Nature likes things to be in balance or equilibrium. ‘Balance’ where moisture in the atmosphere is concerned is 100% water or ‘relative humidity’. The dryer the air is the more water is absorbed into the air as nature tries to attain 100% relative humidity.

People are often confused about the need for foundation watering during our normal rain cycles. During the summer when it is usually very hot and very humid less water may be pulled out of the ground by the atmosphere than during the winter months when the temperature is lower but the humidity is low. As you know from living here, when the humidity is high you sweat and your clothes get wet. Right now, because of the low humidity, your skin is drying as fast as or faster than you can sweat. So you and your clothes stay dry.

But the concept is the same for the ground. As our weather is currently hot and dry, the rate of absorption of water from the ground into the atmosphere is very high.

If your foundation is not showing signs of differential movements or “settlement” don’t do anything. Newer foundations are designed with deeper grade beams, or stiffeners, for the foundation, and these beams are spaced closer together. If your foundation is standing and performing well even though the ground is losing or has lost contact with the foundation, your foundation is actually doing what it was designed to do. You don’t need to help it.

If you water your foundation when it doesn’t need help and you cause an “edge lift” to your foundation, you may destroy the integrity of your foundation.

If your foundation is performing, water your yard enough to keep your vegetation alive. Azaleas are great indicators of ground moisture. As soon as the soil around an azalea dries the azalea will wilt. It is, after all, a swamp plant.

If your foundation is “settling” get soaker hoses. Soaker hoses are black hoses made of recycled car tires. They have small holes that will actually “sweat” water through the hose thus limiting the amount of water used. Put the hoses as close to the foundation as you can. In normal times and over a prolonged period of time it is not so important that the hose be placed as close as possible to, preferably against, the foundation. Right now it is important to get more water to the area that is causing the problem and not to have to rely on the “radiation” of water (water moves vertically, horizontally and diagonally through clay soils).

Turn your outside faucet that you have attached the soaker hose to all the way open to get water throughout the length of the hose. Then turn the faucet down to where the hose “sweats” rapidly. Then leave the hose on and do not play with it anymore.

As the soil absorbs the water the soil will begin to swell or expand. As the soil comes back into contact with your slab, the soil will push your slab back into its proper plane. That means that the diagonal cracks in your walls will try to close, your doors and windows will go back to their “level” condition and the slopes in your floors will flatten out. Be aware that if the cracks in the walls cannot close because of debris in the cracks, cracks in open in the opposite direction to relieve the stress on the wall. So more cracks many mean that your foundation is actually moving in the proper direction.

When that happens, reduce the amount of water you are applying to the soil. You will need to adjust the amount of water you are adding to the soil depending on weather conditions and depending on the future movements of your foundation.

Do not over water your foundation. This can cause the edge or exterior of your foundation to be raised higher than the interior of your foundation. The primary design consideration of your foundation is to prevent the perimeter of the foundation from “settling” when compared to the center of your house. Your foundation is not really designed to prevent the edge of your foundation from rising higher in elevation than the center of your foundation. If that happens, your foundation can really be damaged. Understand that what I am saying about the design of your foundation is not a literal truth but it is true. The primary differential movement of foundations in expansive soils is the edge settlement relative to the center of the house so that is primarily what the engineer who designed your foundation is trying to prevent. You should understand that engineers design for the common events. No one could have foreseen that our normal swamp might become a desert.

If you are not sure about the performance of your foundation of about the type of soil that is supporting your foundation, hire a professional who actually does know about soils.