Roots in the sewer, stopped at the joint.

01 /Why do tree roots get into sewer lines?

Tree roots get into sewer lines because a leaking joint is the best source of water, air and nutrients in the surrounding soil. Older laterals made of vitrified clay or concrete were laid in short sections, with a joint roughly every 0.6 to 1.2 metres, sealed with mortar, jute or early compounds that shrink, rot and crack. Each opened joint leaks humid air and a little wastewater, keeping a small halo of soil permanently damp.

Fine feeder roots growing through the loose trench backfill reach that halo, branch heavily, and slip through the gap. Inside, they have constant moisture and grow into a curtain that snags toilet paper and grease. The root section in the joint thickens every year, prying the joint wider. That is why root problems tend to get worse over time, and why cutting alone never ends them.

Depth does not protect a line as much as people assume. Prairie laterals are commonly 1.5 to 3 metres deep to stay below frost, yet roots follow the softer, better-aerated backfill of the original trench straight down to the joints. Dry summers make things worse: when surrounding soil is parched, the damp zone around a leaking joint can be the most dependable water a large tree can reach, which is why many first backups arrive in late summer or fall.

Plastic pipe changes the picture. Solvent-welded ABS and PVC have few joints, and those joints are chemically fused, so roots usually need a crack, a poorly seated gasket or a transition coupling to older pipe before they can get in. That is why the same tree can be a serious problem on one street and harmless on the next.

Read the full mechanism in how tree roots get into sewer pipes, and see why older clay and concrete neighbourhoods suffer most.

02 /Which trees cause the most sewer root problems?

The trees that cause the most problems are fast-growing, water-hungry species with wide root systems: willows; poplars, aspen and cottonwood; silver maple; Manitoba maple; and American and Siberian elm. Green ash, birch, spruce and fruit trees are moderate. Pines, small ornamentals and most shrubs are lower risk.

Species is only part of the picture. The pipe's joints matter more: a willow over fused plastic pipe can be less trouble than a spruce over mortared clay. The Root Risk Calculator combines species, distance, pipe material, age and history into one band. For planting, see the worst trees and sewer-safe trees and shrubs, then check a planned spot with the Planting Distance Checker.

03 /Cut, treat or fix: how do you stop roots for good?

You stop roots for good by removing the openings they use. Mechanical cutting clears the pipe but leaves the joint open, so roots typically return within one to two growing seasons. Chemical products, where legally registered and used per label, can slow regrowth after cutting but also leave the joint open. Lining, point repairs, pipe bursting or replacement eliminate the joints.

The decision depends on what a camera inspection shows. See mechanical root cutting, how fast roots grow back, chemical root control and permanent root fixes. Household remedies such as salt, bleach and vinegar do not clear a root mass, for reasons set out in what dissolves tree roots, and the most common permanent fix is explained in sewer lining for tree roots.

04 /Whose tree, whose pipe, and who pays?

In most Canadian municipalities, responsibility follows the pipe, not the tree. Homeowners usually maintain the lateral from the house to the property line; the municipality commonly handles the portion to the main, though some cities assign more to owners. Roots from a boulevard or neighbour's tree in your section are generally still yours to clear. Boulevard trees are protected by bylaw, so you cannot prune or dig near them without permission.

Evidence settles most questions: camera footage with a distance counter and a surface locate showing exactly where roots enter. Details are in whose tree, whose pipe. Calgary readers can start with the Calgary guide and call 311 to confirm City rules. If several houses on the street back up together, the problem may be in the public main; see roots in the main sewer line. Home insurance rarely pays for the roots or the pipe, though a sewer backup endorsement may cover the damage; the insurance guide explains the difference.

05 /What should you do first?

1. If you have a backup now

   Stop using water, keep clear of standing sewage near electrical equipment, and have the line cleared from the main cleanout.

2. Get the line filmed

   After clearing, a camera inspection shows material, joints, cracks and the route. Keep the recording.

3. Score your trees

   Run each nearby tree through the Root Risk Calculator, including neighbour and boulevard trees.

4. Price both paths

   Compare a ten-year cutting cycle with a permanent repair using the cost guide.

5. Plant smarter

   Keep new trees off the sewer route and choose smaller, less water-hungry species.

Not sure how urgent your situation is? How serious are roots in a sewer line sets out the stages from fine roots to structural damage. Buying a house where the sewer scope found roots? Start with roots found at a home inspection.

SewerRoots.ca is part of the independent HAUSE Sewer information network. It is not a plumbing contractor. For inspections, see SewerInspector.ca; for jetting, SewerJetting.ca; for comparing prices, SewerQuotes.com. When you want contractors to price root cutting, lining or replacement, request quotes.

Frequently asked

All questions →