In the DFW area root barriers are often installed to prevent foundation repair. In this article we are going try to answer many of your questions about root barriers and why they are one of the causes of foundation problems.
What is unique about the DFW area that causes root barriers to be needed? How deep should root barriers be installed? What kind of material is used for root barriers? What is the proper installation method for root barriers? Will root barrier installation damage my tree? Why do builder’s place young trees so close to new houses? How much does the installation of a root barrier cost? Will the installation of a root barrier lift my foundation and eliminate the need for further foundation repair?
The Need for Root Barriers
Why are root barriers needed in the DFW area? What is different about Dallas soil? Dirt is dirt, right?
There is a very compelling reason for the need for root barriers. Our soil contains a high percentage of clay in the Dallas area. Clay is extremely sensitive to changes in moisture. Why? Let’s get down to the molecular level. Clay particles are extremely thin and flat. They are on the order of 1/1000th the size of a single grain of sand. They are held together by atomic level molecular adhesion. Add water, and water molecules begin to fill the gaps between clay particles. The gaps expand. When the gaps expand, the clay soil expands in volume until the bonds of molecular adhesion break. Then, the clay turns to mud. Remove water from clay soil and the opposite occurs, the soil contracts. The range of expansion and contraction in DFW can be as much as 8-12 inches.
During dry, hot DFW summers, tree roots seek out water from wherever they can. A mature tree may need 100 – 150 gallons per day. In the absence of a well-managed watering program, soil under the foundation becomes the last source of water in your yard. Roots reach out, acting like little straws so that the tree can suck up every last bit of water. Once they have sucked it dry, the roots grow longer and seek out still more water.
Unless water is evenly removed from under a foundation, the soil will provide less support in drier areas. This localized lack of support puts tremendous stress upon a foundation, leading to cracks and breaks and sagging.
The goal of a root barrier is to keep the water-sucking tree away from the foundation so that moisture remains constant throughout the underside of the foundation.
What is the proper installation method for a root barrier?
Root barrier installation is fairly straightforward. Root growth is predictable. It normally occurs in the oxygen rich top 20 inches of the soil, extending out until it finds water. As an interesting aside, the driest part of your yard in the summer is that area under the tree.
Trees with taproots are different, such as those of a pecan tree. Pecan tree taproots go down and down to reach deep water. We don’t need to worry about trees with taproots. It is those trees with shallow surface roots, which cause all the trouble.
Surface roots have been known to extend outward 2-3 times the height of the tree. Since all this outward growth is normally in the top 20 inches, we only need to build a shallow barricade. To be on the safe side, Granite Foundation Repair installs root barriers to a depth of 36 inches. The barrier is brought all the way to the surface to impede shallow roots.
Granite typically digs a root barrier trench between the tree and 3-5 feet away from a foundation. The barrier should be installed so that it intersects a radial line from the tree to the foundation. Roots crossing the trench are cut off. If the root barrier is close to the foundation, moisture will be wicked from under the foundation by roots on the opposite side of the barrier. As an added precaution against root intrusion, rock salt is placed in layers with fill soil on the tree side of the barrier.
Will Installation of Root Barrier Damage a Tree?
While there is a small chance of tree damage by cutting the roots, that is not usually the case. Keep the barrier at less than 180 degrees around the tree, and 5-10 feet from the tree. The further distance the better.
Be certain to provide extra water for the tree during the first year after a root barrier has been installed. A generic root stimulant will help the tree put out new roots to replace the ones that have been cut off.
Root Barrier Materials
A number of materials are used as root barriers. The materials are usually impermeable to water, which prevents a tree from drying the soil on the foundation side of the root barrier. There are some permeable barriers on the market, which are impregnated with chemicals that will retard the growth of roots for 10-15 years.
Root barriers made of polyethylene have an infinite life. Granite Foundation Repair uses a high-density polyethylene impermeable geo-membrane that is 80 mils thick, 36 inches wide and comes in 200 feet long rolls.
Why do Builders Place Young Trees so Close to a New House?
In new house construction the placement of trees is an aesthetic rather than practical consideration. Young trees close to a house will most certainly cause foundation problems in 10-15 years. By then the builder’s warranty has run its course and the builder is absolved of all responsibility.
Cost of Root Barrier
A root barrier costs in the range of $60-$70 per foot in 2017. The price pales in comparison with the cost of foundation repair and the cost of repairing collateral damage from foundation movement.
Will Installation of Root Barrier Solve My Foundation Problem?
Once a root barrier is installed, the soil under the foundation can begin to re-hydrate. Within a year or two, the soil might possibly expand sufficiently to eliminate the need for foundation repair. More often than not, foundation and structural sag (walls and roof) will impede the return to a normal, acceptable level. The foundation will still require structural underpinning with piers.