Why roots get in
A cracked pipe or an open joint leaks a small amount of water and nutrient rich vapour into the surrounding soil. Fine root hairs grow towards it, reach the gap and pass through it. Once inside a pipe with a permanent water supply and no competition, they thrive, thickening from hair fine strands into a dense mat within a couple of seasons.
The mat itself is not usually what blocks the drain. It catches paper, wipes and fat, and the accumulated material is what stops the flow. That is why a root blocked drain often clears very suddenly when it is jetted and then blocks again a few months later.
Which trees cause the most trouble
Willow, poplar and ash are the worst offenders and are all common on older Scottish plots and along boundaries. Silver birch, sycamore and cherry are frequent culprits in suburban gardens. Leylandii and other fast growing conifer hedges planted close to a boundary run cause a surprising amount of trouble for their size.
Distance matters as much as species. A root system commonly extends well beyond the canopy, so a mature tree fifteen metres away can reach a drain that a young tree three metres away cannot. Where a drain runs along a boundary hedge line, assume roots are a candidate whenever repeat blockages occur.
How roots are removed
High pressure jetting with a root cutting nozzle is the standard method, and for a light infestation it is sufficient. Where the mass is heavy or has been in place for years, a mechanical cutter is used, which is a rotating head driven along the pipe that mills the roots back to the wall and removes any hard scale bonded to them.
After cutting, the run is surveyed. This is the step that matters, because the camera then shows the defect the roots entered through, which is invisible while the mat is in place. Without that inspection you have bought a few months rather than a repair.
The repairs that actually keep them out
- A patch liner over a single entry point, sealing that joint or fracture permanently.
- A full length liner where roots have entered at several joints along the same run.
- Excavation and replacement where the pipe has been displaced or broken open by root growth.
- Rebuilding a chamber where roots are entering through failed benching or brickwork.
Chemical treatments and why we are cautious
Root killing foams containing herbicide are used in some parts of the industry. They can knock back regrowth for a season, but they do not repair the defect, they need repeating, and their discharge into the sewer network raises reasonable environmental questions. We would rather seal the pipe than dose it repeatedly.
Copper sulphate poured down the toilet, which is a persistent piece of internet advice, does very little in a flowing pipe and is not something we recommend.
Prevention when planting or building
If you are planting near a known drain run, keep large species well away and prefer shallow rooting ornamentals close to the line. When a drain is being replaced in an area with mature trees, a continuous jointless run or a lined section removes the opportunity entirely, which is worth the small extra cost.
Where a neighbour's tree is the source, the drainage repair remains the responsibility of whoever owns the drain, but a survey with footage showing the entry point is a useful thing to have before any conversation about the tree itself.
A realistic maintenance approach
Where a defect has been sealed, the problem is over and no ongoing treatment is needed. Where sealing is not practical yet, for example because a repair is being budgeted for, an annual cut and jet before the growing season keeps the run usable and stops the mat becoming a solid mass that is far harder to remove.
We will tell you which of those two positions you are in after the first survey, and we do not sell repeat root cutting as a substitute for a repair that would end the problem for good.
Questions we get asked
Can I be made to remove a tree because of drain damage?
Rarely, and it is a civil matter. Sealing the pipe is nearly always the practical remedy rather than felling the tree.
How quickly do roots grow back?
In a defect that has not been sealed, a mat can re-establish within a single growing season, sometimes faster in a warm wet year.
Are roots covered by insurance?
It depends on the wording and on whether the footage shows a fracture with a mechanical cause. Many policies exclude gradual root ingress.
Will jetting damage the pipe?
Correctly set jetting does not damage sound pipework. Where a pipe is already fractured, jetting can reveal that, which is why we survey afterwards.