Keeping Tree Roots Away From The House Foundation

You hear a lot about tree roots causing concrete foundation problems for houses that sit on expansive clay soils and may be wondering how that can be.

In my travels around the Internet I’ve learned the trouble is two-fold. Large trees can suck huge amounts of water from the soil. If thirsty roots get under your slab, they can reduce the moisture content of the soil and cause settling.
Tree roots under the foundation can also worm their way into the plumbing causing leaks and again changing the condition of the soil under the foundation. Heaving of the slab can occur.

Enter the root barrier, sometimes called “root capping.” Here is what the Foundation Performance Association has to say about root barriers:

Maintenance systems should not be considered a repair; although they will enhance the performance of the foundation. Below is a description of a foundation maintenance system and typical problems that may cause poor performance.

3.1 Root Barriers

Root barriers are designed to stop the growth and moisture draw of roots under and in the proximity of the foundation. A trench is dug in the intended area and a barrier of concrete, polyethylene, biocide treated mesh, or other material is placed to block the future growth of roots. Most barriers are 48” or less.

A. Soil expansion and contraction will occur with seasonal weather changes. The mesh root barrier
will allow moisture to penetrate. The impervious barriers will not allow moisture to penetrate.

B. Caution should be utilized when water leaks occur between the impervious root barrier and the
slab. The source of moisture may be from the plumbing lines, sprinkler systems, watering systems, downspouts, or poor drainage. The entrapped moisture can allow soil expansion and contraction to occur, allowing nearby foundations to move.

C. The root barrier may not be deep enough or may have soil above it thereby allowing roots to grow below or above it.

D. Property owner should remove wayward roots if they grow past the barrier.

E. Root barriers that use chemicals to prevent root growth have a limited life and will eventually
become ineffective after ten years.

F. Root barriers that consist of thin membranes such as polyethylene sheeting can be punctured
during installation, allowing small root fibers to penetrate that can eventually grow into large roots.

G. The root barrier installation may sever existing tree roots that already extend under the foundation, and as they wither and die, the surrounding soil could slowly regain its original moisture content, possibly causing local heave of the soil near the severed roots.

H. If the existing tree roots that already extend under the foundation are large in diameter, the decay of the severed roots caused by the root barrier installation could potentially lead to local settlement of the foundation.

It’s always something, isn’t it. If you can’t find root barrier materials at your local nursery or home center, here is one place you can buy it on-line and have it shipped. I’ve notice some foundation repair contractors will also install such barriers for you.

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