There is no universal percentage of a living tree’s roots that can be removed safely. The limit depends on the roots’ size and location, their distance from the trunk, the tree’s condition and the site. A qualified arborist should assess external roots before anyone cuts them.
What determines the safe limit?
Percentages alone are unreliable because most of the root system is hidden and cannot be measured accurately. Roots exposed in one trench or found inside a pipe do not represent a known proportion of the entire system.
An arborist will consider:
- Roots: diameter, whether they are fine or woody, proximity to the trunk, direction of growth and how many would be cut on one side
- Tree: species, maturity, vigour, decay, canopy decline, lean and previous root damage
- Site: soil, moisture, drainage, excavation, compaction and remaining growing space
Large, woody or trunk-adjacent roots may help anchor the tree. Cutting them, especially several on one side, can harm the tree or reduce its stability. Do not cut these roots yourself. If a tree is leaning, declining or appears unstable, keep clear and arrange an arborist’s assessment.
What if the roots are inside a drain?
Clearing fine root growth from inside a drain is different from cutting structural roots outside the pipe. The amount removed from a pipe does not reveal how much of the tree’s root system has been affected.
An appropriately licensed NSW plumber or drainer can clear and inspect a sanitary drain. A drain-camera inspection may help locate where roots entered and identify pipe defects. Cutting or excavating around external roots requires separate arboricultural assessment.
Do not excavate near a drain until concealed water, gas, electricity and communications services have been identified. Leave excavation and repairs to appropriately qualified contractors.
Avoid contact with overflowing sewage and keep children and pets away. Arrange prompt professional help because wastewater may contain harmful microorganisms.
If roots are blocking a drain, our Sydney plumbing team can clear and inspect the pipe; consult a qualified arborist before cutting roots outside it.