How Tree Roots Can Cause Drain Line Clogs

Beech tree with exposed roots.
David Beaulieu

Tree roots growing downward into sewer lines running out in your yard is one thing, but roots growing up from under your house’s slab foundation and invading your toilet is another thing entirely. Believe it or not, this problem is more common than you think.

If you live on a slab foundation, it is possible for the roots to grow up, then along the underside of the slab, creep through the slab where the toilet drain penetrates the slab, and then grow down into the toilet drain pipe. This will, of course, cause all kinds of problems.

Signs of Roots in Drain Lines

  • The most common first sign is a toilet that stops up occasionally, and which generally can be cleared using a plunger. This isn't a definite sign of a root problem, but it can be the first symptom. With low-flush toilets, an occasional stoppage here and there is not uncommon, but if this happens with some frequency, it is an indication that you should keep an eye on things.
  • If the toilet stoppages become more frequent and more stubborn, the likelihood that you are dealing with roots in the drain becomes greater. In some cases, the toilet eventually becomes so blocked that it cannot be cleared with a plunger. Again, the occasional stubborn stoppage is not by itself an indication of a problem. What you need to look out for is a recurring or worsening problem.
  • A localized drain problem is another sign of roots growing into the drain. It's fairly easy to diagnose this. When your toilet is stopped up, first make sure the other fixtures or other toilets are draining. If other plumbing fixtures are also stopped up, or if the drain waste is backing up into your showers and tubs, then you have a main line stoppage—not a root problem. The main line stoppage needs to be cleared through the clean-out if you have one. But if the stoppage is affecting only one toilet, there is a good chance that the cause is tree roots in the toilet drain line.

What To Do

If you suspect that roots in the drain line are clogging your toilet, first use a toilet auger to try and confirm this. Using a toilet auger extended to the six-foot mark can often reach tree roots in the toilet drain line. The auger may pull back some root remains, so inspect the auger and the toilet bowl. This will verify that you have roots under your toilet.

To solve this problem, you will need to pull the toilet up to access the drain. After the toilet is up, you can see the roots underneath. The solution is to cut all the roots back and remove any roots that may have gotten into the drain line.

Removing Roots in the Drain

NOTE: Wear thick gloves to protect your hands.

  1. Using a pair of clippers or a utility knife cut all visible roots as far back under the slab as you can.
  2. If the roots have grown into the drain, pull the roots out of the drain pipe. The easiest way to do this may be by using a drain machine. Run the drain machine until the drain line is clear.
  3. Once the drain is clear and all the roots are removed from around the flange, you can put root killer between the concrete slab and the drain pipe. Rock salt or root killer should be applied where the roots originally grew up from. Either product can help prevent, or at least stunt, the growth of new roots for several years.
  4. Finish by reinstalling the toilet with a new wax seal. Level your toilet with shims, bolt it down, hook up the water line, and put new caulking around the base of the toilet.