What the problem usually is
Roots spread widely and close to the surface, and they are drawn to water. Common complaints are roots lifting a drive or path, roots in drains, and cracks in a building that might be subsidence. The cause is often not what it looks like:
- Drains. The Arboricultural Association says roots usually enter only drains that are already damaged and leaking, and that removing the tree rarely solves the problem because the damaged drain is still there. The RHS likewise advises lining or replacing old leaking drains, with tree removal as a last resort.
- Paving and drives. Roots can crack hard surfaces, usually superficially. The Arboricultural Association lists doing nothing, repairing the cracks, replacing the surface with one designed to accommodate roots, or pruning the roots or removing the tree.
- Buildings. Damage to buildings is much rarer than damage to drives and drains. The RHS says subsidence is generally a problem only on shrinkable clay soils, and that lifted paving does not mean roots are damaging the house.
Root pruning, done carefully
A tree surgeon can cut roots to deal with localised damage, for example where a root is lifting a path some distance from the trunk. The RHS says this can be done if the damage is localised, and a barrier fitted to stop regrowth. It also warns that large roots close to the trunk should not be cut, because that can destabilise the tree. Before roots are cut, a good firm will want to know where the roots are, how big they are and what the tree needs to stay upright.
Root barriers and other options
- Root barriers are a physical sheet in the ground that deflects roots downward or away from a structure. The RHS notes they are usually not feasible to install to sufficient depth, and roots may grow under them, so they are best planned at planting time or with a specific, localised problem.
- Air spading and soil decompaction. Compressed air can remove soil around roots without cutting them, so roots can be found, assessed or pruned cleanly, or compacted ground can be loosened. Ask a firm whether they offer it if the roots are important to the tree.
- Engineered surfaces. Raising a path on a flexible base, bridging over roots or changing the paving type can avoid root cutting altogether.
What to ask a firm
- Which roots are involved, how large are they and how far are they from the trunk?
- Will they dig by hand or use air tools to expose the roots first, so nothing is cut blind?
- What is the effect on the tree, and is a regrowth barrier planned?
- Is the real problem a leaking drain or a failing surface that needs a different trade? A drainage survey (CCTV) is often the way to find out.
Root protection areas
When building near trees, arborists work out a root protection area using British Standard BS 5837:2012. For a single-stemmed tree, the starting point is a circle with a radius 12 times the trunk diameter measured at 1.5 metres, capped at 707 square metres, then adjusted for site conditions. It is a minimum area to keep the tree healthy, not a safe distance for digging. Trenching for services or foundations inside it needs an arborist's advice first.
When not to cut roots
- Large structural roots near the trunk.
- Any tree with a Tree Preservation Order or in a conservation area without checking first. Root cutting can damage a protected tree, so see our TPO guide.
- When a building is cracking. Root cutting is not a recognised fix for subsidence and can destabilise the tree; if a tree is confirmed as the cause, the usual routes are crown reduction or removal, after an expert report. Tell your insurer and read our guide to mortgage and insurance tree reports. A tree survey can show whether a tree is likely to be involved.