In my previous blog (Part1), I discussed the “requirement” for Texas homeowners to add water to the soils around their slab foundation. This is being done to attempt to limit foundation movement caused by clay soils drying out.
Slab foundations in North Texas are usually not installed in a stable bearing stratum (like rock) but are installed on the surface of expansive clay. Being installed on the surface ensures that the foundation is in (and on top of) the Active Zone. The Active Zone is that depth below the ground surface where the moisture content does not vary. The soil below this Active Zone is reasonably stable, but the soil above the Zone contracts and swells in a cyclical manner, depending on the season (wet/dry). This shrink / swell can push a slab foundation around.
So the goal of adding water to the clay soils around the foundation is to attempt to keep the moisture content of the clay in the Active Zone as constant as possible. Doing this minimizes (but does not necessarily eliminate) the potential for slab settlement. at least the settlement that is caused by the soils becoming desiccated. (Slabs settle for reasons other than desiccation.)
There are three methods commonly used by homeowners to add water to the clay.
The most common method of maintaining the soil moisture is by laying soaker hoses on top of the ground around the foundation. Even though this technique has its difficulties, it is the simplest and least expensive. It also makes it easy to see if the hoses have been damaged and need replacement. It is usually recommended that the hoses be placed 18” to 24” from the foundation.
One problem with soaker hoses laid on top of the ground is that a lot of the water can be lost to evaporation or run off. Another problem is that they get kicked around and cut up by the landscaping crew.
Some homeowners bury the soaker hose which protects them from lawn mowers, but this makes it more difficult to see if they have been cut, damaged, etc.
Automatic Lawn Sprinkler (Irrigation) System.
If a homeowner is planning to have an irrigation system installed, here are a few things to discuss with the irrigation (licensed) specialist:
• If I were going to have a sprinkler system installed, I would have a supply line installed parallel to and about 4 or 5 feet from the foundation (to minimize the bad effects if a leak developed in the system). I would then install short radial lines to reach the foundation area (with the sprinkler head about 6” or so from the foundation).
• I would not install the water supply line only a few inches from the foundation.
• Regularly check the sprinkler system for leaks, including at the valves.
• In the Dallas / Ft. Worth area, I would install the irrigation pipes at least 12” below the surface to minimize the danger of an extended period of freezing weather. However, the irrigation technician will know the minimum depth. I had a neighbor whose new sprinkler system was buried only 8” and portions of it froze during a particularly cold winter. Your local city building code department probably has minimum guidelines on this.
• If the purpose of the irrigation system is to keep the soils near the foundation at a constant moisture content, then there should be 3 or 4 zones dedicated to the foundation only (possibly more depending on the size of the house). This way, it is not necessary to water the entire yard when the foundation soils need water.
• Do not allow the sprinklers to spray water on the brick/siding.
•DO NOT suddenly begin an aggressive watering program if the clay soils are in a desiccated state (like during a drought or in the dry summer months). In other words, do not suddenly put a lot of water into the clay soils around your foundation. To do so, can cause upheaval of the slab. It is best to allow Mother Nature to rehydrate the soils during the winter/spring months and then start a watering program prior to the summer drought kicking in.
• Too many homeowners water only enough to keep the upper few inches of soil moist; this is inadequate.
• One typical indicator that the soil around a foundation needs moisture is that the soil begins to pull away from the foundation. When this occurs, moisture is needed: do not pour water into the gap!
• During the prolonged summer drought, it may be necessary to water the soil around the foundation several times a week. A word of caution though – do not suddenly overwater dry expansive clays! The goal is to keep the soil near and under the foundation at a consistent moisture content (neither wet and/or muddy nor dry and cracked).
I have seen homeowners who had just purchased their homes and began their watering the soil program only to cause the clay to expand, heaving their foundation upwards. They later found out that the soils around the foundation had not been “watered” for months and were in a desiccated condition. I do not have an answer to this dilemma. My advice is to be careful and be gradual in your watering program. As stated elsewhere in this blog, if it is new home, talk with the builder and/or his engineer about their recommended watering guidelines. If an older home, let Mother Nature rehydrate the soils, then you start your watering program.
In the next blog, I will discuss the pros and cons of a buried drip irrigation system.
For additional information, go to http://www.GeoDFW.com.