Watering the foundation of a house to prevent damage to plumbing, exterior and interior walls, structural members, and the foundation itself is helpful, according to several Texas engineers who specialize in soil mechanics and construction.
Despite outdoor watering restrictions, the value of protecting a home by watering the foundation is recognized by local water districts and utilities. Under the North Texas Municipal Water District Stage 3 restrictions and Dallas Water Utilities Stage 1 criteria, foundation watering is an exception to the outdoor watering restrictions. Richardson – a NTMWD member city – has this statement on its website: “Use of drip irrigation systems and soaker hoses to protect foundations is allowed, except between the hours of 10 a.m. to 6 p.m. (Recommended maximum 2 hours when needed.)”
A different foundation watering rule may apply in other NTMWD member cities, which include Allen, Farmersville, Forney, Frisco, Garland, McKinney, Mesquite, Plano, Princeton, Rockwall, Royse City and Wylie.
Dallas allows foundation watering “on any day of the week during the allowed watering hours [midnight-10 a.m. and 6 p.m.-midnight]. Foundations may be watered with a soaker hose or a hand-held hose equipped with a positive shutoff nozzle only," according to savedallaswater.com.
The most common cause of foundation problems in North Texas — even when there is no drought — is the “very active zone of clay soil running through North Texas up into Oklahoma,” says engineer Ian Ray of Evergreen Structures in Dallas.
If your home is built on clay soil, which is likely if you live in North Texas, then the house’s foundation is floating more or less on a sponge, according to a Texas A&M University soil mechanics expert.
Clay soil is “like a sponge,” says Jean-Louis Briaud, professor of civil engineering at Texas A&M in College Station. “The sponge changes significantly when it’s dry and when it’s wet.” And similar to a sponge, clay soil shrinks and swells with moisture changes, says Briaud, president of the International Society of Soil Mechanics and Geotechnical Engineering.
What is “active” about clay soil, according to Briaud, is “related to capillary forces,” which cause water to be attracted to and adhere to the surface of the very tiny silica clay particles, swelling them. When the moisture on the particles dries, they shrink. That’s what causes the soil to move, but “it’s very difficult to predict how the soil is going to move” when moisture content changes, he says.
“What damages houses is when the foundation wants to bend” due to uneven moisture under and around it, Briaud says. He favors “waffle slabs,” which have beams — 3 to 4 feet deep and 1 foot wide — going in both directions in a crisscross pattern under the slab. “It’s mighty stout,” he says, and if this type of foundation moves, the whole foundation will move, but it won’t bend and crack under the pressure.
Ray says, however, that most North Texas houses have conventional slab or pier-and-beam foundations that are subject to damaging shifts “depending on the clay content and the amount of moisture in the soil.”
The purpose of watering a foundation, Ray says, is to keep the soil’s moisture consistent around and under the slab. “The goal is to keep the soil’s moisture at a 5 on a scale of 1 to 10 so it doesn’t get very dry, 1, or very wet, 10. Consistent moisture is a key.” There must be “some means of watering, even in the winter,” he says.
Soaker hoses “are effective but you have to have good drainage” that steers water away from the foundation. Other issues to consider: Does rainwater collect around downspouts instead of draining away from the foundation? Are trees planted so close to the house that roots go under a slab foundation?
The problem with tree roots can be significant, according to Gary Morgan, a Richardson arborist. “The motivation of every tree’s root system is to find moisture, which can be abundant under foundations.” Tree roots, which can consume hundreds of gallons of water per week, would be especially attracted to moisture under slab foundations in a drought, he says.
The danger is that “the roots may invade a wet area and suck it dry,” Morgan says, “then some of the tree’s other roots will start looking elsewhere and the old roots will die under the slab and will leave voids, which can cause even more foundation problems because it will collapse the space under the slab.”
The best way to avoid tree roots invading a foundation, Morgan says, is to plant trees an appropriate distance from the house. Since different types of trees’ root systems behave in different ways, Morgan recommends consulting with a certified arborist or horticulturist, before adding a tree to the property, for recommendations on the appropriate tree based on its role in the landscape.
However, if the tree is already in place, the typical way to avoid or deal with invasive tree roots, Morgan says, is to install a root barrier.
“Every arborist, landscaper and foundation repair company will have a different way to do this,” Morgan says. Generally, however, the basic method involves digging a trench parallel to the foundation and “putting some kind of material in the trench to retard the growth of the roots.” An older, effective material is charcoal. Newer materials include fabrics made of nylon or metal.
Trees are not the only plants that can be a problem for foundations, according to Ed Scoular, a Plano-based construction engineer and soil expert who is president of Independent Foundation Engineers.
“Shrubbery and other plants have a great thirst for water and will act like a pump to pull it out,” Scoular says. “Where you have the settling of a foundation is probably where there are a lot of plants and large demand for water. The smaller and fewer the plants, the less effect on the foundation.”
Tim Tune is a Fort Worth freelance writer.