Tree Roots vs. Sanitary Sewer Lines

Root Growth in Pipes:

Roots require oxygen to grow, they do not grow in pipes that are full of water or where high ground water conditions prevail. Roots thrive in the warm, moist nutrient rich atmosphere above the water surface inside sanitary sewers.

The flow of warm water inside the sanitary sewer service pipe causes water vapor to escape to the cold soil surrounding the pipe. Tree roots are attached to the water vapor leaving the pipe and they follow the vapor trail to the source of the moisture, which are usually cracks or loose joints in the sewer pipe.

Upon reaching the crack or pipe joint, tree routes will penetrate the opening to reach the nutrients and moisture inside the pipe. This phenomenon continues in winter even though trees appear to be dormant.

Problems Caused by Roots Inside Sewers:

Once inside the pipe, roots will continue to grow and if not disturbed, they will completely fill the pipe with multiple hairlike 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 or business.

Homeowners 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 are completing the laundry. A complete blockage will occur if no remedial action is taken to remove the roots/blockage.

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 the root growth will break the pipe and may result in total collapse of the pipe. Severe root intrusion and pipes that are structurally damaged, will require replacement.

Tree Roots in Sewers:

Tree roots growing inside sewer pipes are generally the most expensive sewer maintenance item experienced by City residents. Roots from trees growing on private property an on parkways throughout the City are responsible for many of the sanitary sewer service backups and damaged sewer pipes.

Home owners should be aware of the location of their sewer service and refrain from planting certain types of trees and hedges near the sewer liners. The replacement cost of a sanitary sewer service line as a result of damage from tree roots may vary from $1000 to $5000.

Susceptible Pipes to Root Damage:

Some pipe material are more resistant to root intrusion than others. Clay tile pipe, that was commonly installed by developers and private contractors until the late 1980's, was 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.

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 five to seven times the height of the tree.

Root Growth Control:

The common method of removing roots from sanitary 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 auguring are normally just a small fraction of the roots inside the pipe.

To augment the cutting and auguring methods, there are products available commercially that will kill the roots inside the pipe without harming the tree. The use of products such as copper sulphate and sodium hydroxide are not recommended because of negative environmental impacts on the downstream receiving water. Also, these products may kill the roots but they do not inhibit regrowth.

The more modern method used throughout Canada and the United States for controlling root growth involves the use of a herbicide mixed with water and a foaming agent. The foam mixture is pumped into the sewer pipe to kill any roots that come into contact with the mixture. New root growth will be inhibited from three to five years after the treatment according to the manufactures.

A television inspection of the pipe to determine the extent of the root damage before the treatment application is recommended. Consult the yellow pages under the heading of "Sewer Service" for further information o companies that perform television inspections of pipes and root control.

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