The Nemesis of Sewer and Drain Pipes: Tree Roots

Tree roots are the nemesis of sewer and drain pipes in the Puget Sound area. – especially those installed from the early 1900’s through the 1970’s. The Puget Sound area is full of trees and other greenery creating more issues from roots than many other areas of the country. With sewer pipes installed up until the early 1980’s being predominantly made of concrete and clay (PVC became the most frequent material installed in 1983), root damage is a real concern.

Problems with concrete and clay sewer pipes.

• The joints were rarely watertight - even from the first day they were installed.  The narrow end of the pipe (called the spigot) was inserted into the larger end of the next section of pipe (called the bell).  The pipe installer would take concrete or mortar and run a bead around the spigot and bell joint to ‘seal’ it.  The process was repeated as often as necessary to get the sewer to the required length.  Since the joints were often not water proof, small amounts of water would immediately find its way out of the pipe, attracting tree roots.
• Concrete and clay pipes were only in 3’ long sections.  Over the entire length of a typical 100’ long sewer, you will find roughly 33 joints or 33 invitations for tree roots to enter the pipe.
• Concrete and clay pipes are also very heavy.  As the ground moves and shifts over long periods of time, the heavy pipes can sink into the soil. Gaps in the joints are created or worsened.
• These types of pipes are brittle. As they settle, move and shift, they can crack and break creating more potential entry points for the roots.

Once roots have infiltrated the pipe, they will continue to grow in diameter. This further creates or worsens gaps in the pipes.  In severe cases, roots will completely break the pipe apart or crush it - both of which require that section of pipe to be replaced.

Even before the intrusion is significant enough to break the pipe entirely, the roots will still likely obstruct the flow of water and waste in the pipe causing the backups in showers, toilets and other fixtures.  This is generally when we become aware of any of the problems mentioned above.

Solving The Problem

Cutting roots from sewers to provide temporary relief (from a few months to a few years), but the only way to prevent roots from further growing into a sewer once they have begun is pipe replacement or pipe lining. Removal of the tree(s) that have the damaging roots may not solve the problem completely unless the stump is fully removed and cannot grow anymore. Only after the food supply is no longer available to the tree will the roots stop growing. How long this takes can be dependent on the species of tree and how completely it is removed. If you see new sprouts on a stump, it might not be dead.

The photo shows a 28’ 5” root removed from a 4” diameter concrete storm drain in Renton, WA. The pipe was 100% blocked. You can also see a bell and spigot joint still around the root.