Root barrier design
Design of root barriers to protect drains and foundations from nearby trees.
About this service
A root barrier is a vertical sheet or membrane installed in the ground to stop tree roots growing towards something you want to protect. Properly specified, it can keep roots out of drains, away from foundations and clear of paving and boundary walls, while allowing the tree to stay. The design sets where the barrier goes, how deep it must be, what material to use and how the joints and ends are finished so roots cannot simply grow around it.
On London Clay, roots matter for two reasons. They seek out leaking drains and can block or crack them, and they draw moisture from the clay beneath shallow foundations, contributing to seasonal movement. Insurers dealing with subsidence claims sometimes recommend a barrier as an alternative to removing a tree, particularly where the tree is protected, belongs to a neighbour or stands on the street.
We assess the tree and root risk, check soil type and the depth of the structure to be protected, and produce a barrier layout with depth, material specification and installation details for your contractor. Our design goes through our three-step quality control process, with final sign-off by our Head of Engineering. Fees start from £450 + VAT, and the drawings are suitable for pricing and for sharing with an insurer or council.
When you need it
- Tree roots are damaging drains or foundations
- You're building near trees and want protection
- An insurer has recommended a root barrier
What's included
- Assessment of tree and root risk
- Root barrier layout and depth
- Installation details
How it works
- Assess the riskWe identify the trees involved, their species and distance, the drains or foundations at risk and any evidence of existing root damage, such as CCTV findings or roots in a trial pit.
- Set the line and depthWe position the barrier between the tree and the asset, deep enough to extend below the root zone and the foundation level, and long enough that roots cannot easily grow around the ends.
- Specify materialsWe specify a suitable barrier material, jointing method, top detail above ground level and backfill, and note how buried services crossing the line should be sealed.
- Installation detailsWe provide drawings and notes covering trench excavation, root pruning along the line, protection of the tree, and checks the contractor should make before backfilling.
What you receive
When a root barrier works, and when it is not the answer
Barriers are most effective as prevention: protecting new or repaired drains, or stopping roots reaching a wall that has not yet been seriously affected. For subsidence, they work best when installed after roots have been cut along the barrier line, so the clay beneath the house can recover moisture over time. The tree's own health matters too, and severing major roots close to a mature tree may need input from an arboriculturist and, for protected trees, council consent. Our subsidence guide explains how this fits into a wider claim.
A barrier is not a substitute for proper foundation depth on new work. If you are building an extension near trees, the foundations should still be designed to recognised guidance through a tree influence and foundation depth assessment. Where roots have already broken into drains, repair comes first, and a drain repair specification can be combined with the barrier so both are done in one excavation.
Frequently asked questions
Do root barriers actually work?
Yes, when they are deep enough, continuous and finished properly at the ends and top. Most failures come from barriers that are too shallow, have unsealed joints or stop short so roots grow around them. A barrier also only protects what is behind it, so its line has to be chosen carefully against the tree and the asset being protected.
How deep should a root barrier be?
Deep enough to extend below the zone where the tree's roots are active and below the foundation or drain being protected. On clay near large trees this is often well over a metre. The right depth depends on species, soil and what you are protecting, so it should be set by a site-specific design rather than a standard figure.
Can a root barrier stop subsidence from a neighbour's tree?
It can help, particularly where the tree cannot be removed because it is protected or the neighbour will not agree. Installed on your side of the boundary, with roots cut along the line, it stops further moisture extraction beneath your foundations. Insurers sometimes accept it as part of a subsidence solution, often with monitoring afterwards to confirm the movement has stopped.
Will installing a root barrier harm the tree?
Cutting roots along the barrier line does reduce the tree's root system, and very close cuts to a mature tree can affect its stability or health. The barrier line is usually kept at a sensible distance, and for valuable or protected trees an arboriculturist should advise on how much root loss the tree can tolerate.