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Tree root growth

Roots from trees growing on private property and on boulevards throughout Edmonton can cause flooded basements and damaged sewer pipes.

Roots thrive in the warm, moist, nutrient-rich atmosphere above the water surface inside sanitary sewers. The flow of warm water inside the sanitary service pipe causes water vapour to escape to the cold soil surrounding the pipe. The leading tip of tree roots can detect minute differences in moisture and nutrient levels and tend to grow in the direction where these can be found. On reaching a crack or joint in the pipe, tree roots penetrate the opening to reach the nutrients and moisture inside the pipe. This will continue through the winter even though trees appear to be dormant.

Once inside the pipe, roots will continue to grow, and if not disturbed, they may completely fill the pipe with multiple hair-like root masses at each point of entry. The root mass inside the pipe becomes matted with grease, tissue paper and other debris discharged from the residence.

Signs of sewer pipe problems

The homeowner will notice the first signs of a slow flowing drainage system by hearing gurgling noises from toilet bowls and observing wet areas around floor drains after completing the laundry. A complete blockage may occur if no remedial action is taken to remove the roots.

As roots continue to grow they expand and exert considerable pressure at the crack or joint where they entered the pipe. The force exerted by root growth may break the pipe and could cause it to collapse. Structurally damaged pipes may require repair or replacement.

Root growth control

The common method of removing roots from sewer service pipes involves the use of augers, root saws and high pressure flushers. These tools are useful in releasing blockages in an emergency; however, cutting and tearing of roots encourages new growth. The effect is the same as pruning a hedge to promote faster, thicker and stronger regrowth. Roots removed by augering are normally just a small fraction of roots inside the pipe.

A television inspection of the pipe to confirm root damage and determine its extent is recommended.

Root spread

During drought conditions and in winter, tree roots travel long distances in search of moisture. As a general rule tree roots will extend up to 2.5 times the height of the tree, and some species of trees may have roots extending 5 to 7 times the height of the tree.

​Susceptible pipe materials

Some pipe materials are more resistant to root intrusion than others. Clay tile pipe, commonly installed by private contractors until the late 1980's, is easily penetrated and damaged by tree roots. Concrete pipe and no-corrode pipe may also allow root intrusions to a lesser extent than clay tile pipe.

PVC pipe is more resistant to root intrusion because it usually has fewer joints. The tightly fitting PVC joints are less likely to leak as a result of settlement of backfill around the pipe.

Tree types

Various species of trees have different water requirements. Trees that have high water demand characteristics have root systems capable of following water vapour escaping from leaking pipes and will exploit the source of water inside the pipe. The top 5 species of trees to exploit the moisture inside sewer pipes are:

  1. Poplar
  2. Willow
  3. Elm
  4. Ash
  5. Birch

Other trees and woody shrubs commonly associated with sewer root problems are: Maple, Cottonwood, Russian Olive, Apple, Pear, Lilac Honeysuckle and Chokecherry.