Tree Root Subsidence

Causes, Warning Signs, Solutions and Legal Remedies

Tree root subsidence is one of the most common causes of structural movement and it particularly affects residential properties in the south of England. While trees bring significant environmental and aesthetic benefits, their interaction with certain soil types, such as clay, can create risks for buildings.

Understanding how tree root subsidence occurs, recognising the warning signs, and knowing how to mitigate the damage, as well as understanding any legal remedies available, is important for homeowners, insurers and property professionals alike.

What is tree root subsidence?

Subsidence refers to the downward movement of the ground beneath a building’s foundations, causing the structure above to sink unevenly. This can lead to cracking, distortion of walls and structural damage.

It is important to distinguish subsidence from two other forms of movement:

Settlement, which occurs naturally as a building adjusts after construction and is usually harmless.
Heave, which is the opposite of subsidence and occurs when the ground expands and pushes foundations upward.

Subsidence is more serious because it is often progressive, meaning the damage can worsen over time if the underlying cause is not addressed.

Tree-related subsidence occurs most frequently in areas with clay-based soils. Clay soils expand when wet and shrink when dry. During the growing season, trees draw moisture from the ground through their root systems. Where trees are close enough to a building, the resulting loss of moisture can cause the clay to shrink and the ground beneath the foundations to drop. This explains why subsidence damage is often first noticed during late summer or early autumn, when soil moisture levels are lowest.

Large trees with high water demand, such as oak, willow and poplar, are more commonly associated with subsidence, particularly where they are located close to buildings. Root systems can extend well beyond the canopy and may reach distances up to twice the height of the tree.

Buildings with shallow foundations, including older properties, extensions and outbuildings, are particularly vulnerable.

Signs of subsidence

Not every crack in a property indicates subsidence. Minor cracking can occur as a result of temperature changes or plaster shrinkage.

However, certain warning signs may be indicative of subsidence:

Diagonal or stepped cracks in brickwork, often around windows and doors
Cracks that are wider at the top than at the bottom
Cracks wider than 1mm that continue to worsen
Doors and windows sticking as the structure distorts
Rippling wallpaper or cracks at wall–ceiling junctions
Gaps appearing between skirting boards and walls
In more serious cases, sloping or uneven floors

The key question is whether the damage is progressive. If cracks continue to widen or new cracking appears over time, further investigation is usually required.

Investigating the cause

Where subsidence is suspected, insurers typically appoint loss adjusters and specialist experts to investigate the cause of the damage.

Investigations often include trial pits or boreholes near the foundations to assess soil conditions, identify the presence of roots and determine foundation depth. A structural engineer will assess the cracking patterns and structural movement, while an arboricultural expert examines nearby trees to determine whether they are capable of influencing soil moisture beneath the foundations.

In many cases, crack monitoring will also be undertaken. Monitoring studs are installed across cracks and the building is observed over time.

Tree-related subsidence often produces cyclical movement, with buildings moving downward during the summer and recovering slightly during wetter winter months. Continuous downward movement may suggest alternative causes, such as leaking drains.

Establishing the cause requires careful analysis of all available evidence, often over several months.

Potential solutions

The appropriate solution depends on both the cause and severity of the problem. In many cases, relatively straightforward measures can resolve the issue. Arboricultural solutions such as pruning, crown reduction or in some cases, complete removal of the tree, can mitigate or resolve the problem. But professional advice is essential because removing large trees can occasionally lead to ground heave, where soil expands as moisture returns.

Engineers may also sometimes install root barriers to prevent tree roots reaching foundations. However, the most widely recognised solution is underpinning, which strengthens foundations by extending them deeper into stable ground. Unfortunately, underpinning is usually regarded as a last resort due to the cost and disruption involved. Costs can range from £10,000 to £50,000 or more, depending on the property and the scale of the works.

Legal liability and remedies

Damage caused by tree roots is usually dealt with under the law of nuisance, but is rarely straightforward.

Who is responsible?

If someone has trees on their land, they generally have a duty to take reasonable steps to prevent or minimise the risk of damage to neighbouring property.

This duty arises not only when they know that roots are encroaching beyond their boundary. It can also arise where they ought reasonably to have known that a tree could cause damage. Factors such as the size of the tree, its proximity to neighbouring buildings and local soil conditions may all be relevant.

Importantly, a neighbour may be liable for a nuisance that began before they purchased the property if they later became aware, or ought reasonably to have become aware, of the risk and failed to take reasonable steps to address it.

Proving the cause of the damage

A property owner’s assumption that a neighbour’s tree caused the damage is not sufficient. The claimant must prove that the tree roots caused or materially contributed to the damage.

This is often complex because similar symptoms can arise from other factors such as defective construction, leaking drains or general ground movement unrelated to vegetation.

For this reason, subsidence claims typically rely on evidence from multiple experts, including arboriculturalists, structural engineers and surveyors. Their combined analysis helps establish whether tree roots are an effective cause of the damage.

Claims involving council-owned trees

Many subsidence disputes involve trees owned by local authorities. Councils are expected to properly manage and maintain trees under their control.

This can make it easier to argue that a council knew or ought to have known about the potential risk posed by a tree when compared with a private homeowner. However, councils are usually subject to strict consultation requirements and may be reluctant to remove trees due to environmental considerations and negative public.

Legal remedies

If and when liability can be proved, the law generally provides two forms of remedy.

The first is abatement of the nuisance, which may involve requiring the tree owner to take steps to prevent further damage. In some circumstances, the court may also grant an injunction requiring works such as pruning or removal of the tree.

The second remedy is financial compensation. This usually reflects the reasonable cost of necessary repairs, which may include crack repairs, rebuilding damaged structures or, in serious cases, underpinning works supported by expert evidence.

In some circumstances, a property owner may consider claiming for diminution in value where the market value of the property has been affected by its history of subsidence. Properties with subsidence histories can be harder to sell and may attract higher insurance premiums.

Insurance and dispute resolution

Buildings insurance often plays a central role in subsidence claims, particularly in funding investigations and repairs. However, insurers are primarily concerned with the insured risk and may not pursue all potential losses, such as diminution in property value.

Getting independent legal advice early may sometimes be appropriate. Although disputes about tree root subsidence can escalate into litigation, many are resolved through negotiation or mediation, which courts actively encourage. Reaching a practical solution early can often prevent costly and lengthy legal proceedings.

Next steps

Tree root subsidence arises from a complex interaction between soil conditions, vegetation and building foundations. Resolving the issue often requires collaboration between engineers, arboricultural experts, insurers and legal advisers.

While the presence of trees can increase the risk of subsidence in clay-rich areas, careful investigation and proportionate intervention often allow the problem to be addressed without major structural works.

Identifying the cause of movement early and taking appropriate steps to mitigate it remains the most effective way to protect both property and neighbouring relationships.

If you would like to discuss any of the issues raised in this article, please get in touch.

The legal content provided by RSW Law Limited is for information purposes only and should not be relied on in any specific case without legal or other professional advice. 

Insights

Jonathan Woodroffe

Lucy