Understanding Trees, Roots and Foundation Movement

If you have noticed cracks appearing in your walls or floors, one of the first questions you might ask is: could a nearby tree be causing subsidence?

It is a common concern for homeowners, particularly when large trees are growing close to buildings.

The relationship between trees and subsidence is more complicated than simply saying that tree roots damage foundations. In some circumstances, trees can contribute to ground movement that affects a building, particularly where buildings are founded on shrinkable clay soils.

However, a tree growing close to a building does not automatically mean it is causing subsidence, and removing a tree without understanding the cause of the movement can create further problems.

Understanding the relationship between trees, roots, soil and buildings is therefore important before deciding whether tree surgery is necessary.

What Is Subsidence?

Subsidence occurs when the ground beneath a building moves or loses volume, causing the building's foundations to move with it.

This movement can result in cracks appearing in walls, floors or other parts of a building.

There are several potential causes of subsidence, including changes in soil conditions, leaking drains, poor foundations, ground disturbance and vegetation.

Trees can be one contributing factor, but they are not responsible for every case of subsidence.

How Can Trees Contribute to Subsidence?

Tree roots naturally grow through the soil in search of water and nutrients.

During periods of dry weather, trees can take significant amounts of water from the surrounding soil. On certain soil types, particularly shrinkable clay soils, removing water can cause the soil to shrink.

If this shrinkage occurs beneath or close to a building's foundations, it can contribute to ground movement.

This is where trees can potentially become a factor in subsidence.

It is not simply the presence of roots underneath a building that causes the problem. The interaction between the tree, soil, weather conditions, roots and building foundations needs to be considered.

Why Does Clay Soil Matter?

The type of soil beneath a property is an important part of understanding potential tree-related subsidence.

Clay soils can expand when they absorb water and shrink when they lose water.

This means that prolonged dry weather can cause significant changes in soil moisture levels.

Where a tree is taking water from clay soil close to a building, its presence may contribute to the drying and shrinkage of the soil.

However, this does not mean every property with clay soil and nearby trees will experience subsidence.

The depth and type of foundations, the size and species of the tree, its distance from the building, soil conditions and local weather patterns can all influence the situation.

Can Tree Roots Damage Foundations?

It is often assumed that tree roots physically push through foundations and cause buildings to crack.

In many cases, this is not the primary mechanism involved.

Roots can exploit existing weaknesses and gaps, particularly around drains or existing cracks, but tree-related subsidence is more commonly associated with changes in soil moisture and subsequent soil shrinkage.

This distinction matters because removing a tree without establishing the actual cause of the problem may not resolve the issue.

What Are the Signs of Possible Subsidence?

There are many reasons why cracks can appear in a building, so a crack does not automatically mean that a property is suffering from subsidence.

Potential signs can include:

Cracks that appear or become noticeably wider over time
Diagonal cracks around doors or windows
Doors or windows becoming difficult to open or close
Sloping or uneven floors
Cracks that extend through multiple areas of a building
Signs of movement that appear alongside a nearby tree

However, these symptoms can have other causes.

For example, buildings naturally move and settle, and changes in temperature and moisture can cause materials to expand and contract.

If you are concerned about possible subsidence, it is important to seek advice from an appropriately qualified building professional or structural engineer rather than assuming that a tree is responsible.

Should You Remove a Tree If You Have Subsidence?

Not necessarily.

This is one of the most important points to understand.

Tree removal should not be the automatic response to suspected subsidence.

Before any tree is removed, the circumstances should be properly investigated to establish whether the tree is actually contributing to the problem.

In some cases, alternative tree management may be possible.

Depending on the species, condition, location and circumstances, options could include:

Monitoring the tree
Pruning or reducing the crown
Managing competing vegetation
Carrying out further investigation
Removing the tree where it is established that it is contributing to an unacceptable risk

The appropriate solution depends entirely on the individual site.

Why Tree Removal Can Sometimes Create Another Problem

Removing a tree changes the way water is taken up from the surrounding soil.

If a tree has been contributing to the drying of shrinkable clay soil, removing it can allow the soil to regain moisture.

This can cause the soil to swell.

The resulting ground movement can potentially affect a building, particularly where the foundations are susceptible to this type of change.

This is sometimes referred to as heave.

For this reason, removing a large tree near a building should not be treated as a simple solution to suspected subsidence.

The potential consequences of removal need to be considered as part of the wider assessment.

What Should You Do If You Are Worried About a Tree and Subsidence?

If you have a large tree close to your property and are concerned about subsidence, don't immediately arrange for the tree to be removed.

Start by getting the building movement properly investigated.

A structural engineer or other suitably qualified professional can assess the building and help establish the likely cause of the movement.

An arborist can then assess the tree and its condition, including its species, size, location and potential relationship with the surrounding area.

In some circumstances, specialist investigations may be needed to establish whether vegetation is contributing to the problem.

This approach helps avoid making decisions based on assumptions.

What If the Tree Is Protected?

You should also check whether the tree is protected before arranging any tree work.

A tree may be protected by a Tree Preservation Order (TPO) or may be located within a conservation area.

If so, permission or notification may be required before certain works can be carried out.

Even where a tree is suspected of contributing to subsidence, the correct legal process still needs to be followed.

Trees and Subsidence: Why Professional Assessment Matters

The relationship between trees and buildings is complex.

A tree close to a property is not automatically a problem, and a crack in a wall does not automatically mean that a nearby tree is responsible.

The condition of the tree, its species, size and water demand need to be considered alongside the soil, foundations, weather conditions and evidence of building movement.

Most importantly, tree removal should not be the first assumption when subsidence is suspected.

Understanding the cause of the problem first allows the most appropriate solution to be considered, whether that involves monitoring, tree management, further investigation or, where justified, removal.

Concerned About a Tree Near Your Property?

Beechwood Trees and Landscapes provides professional tree surgery and arboricultural services across Coventry, Rugby, the West Midlands and beyond.

If you are concerned about a tree's condition, location or potential impact on your property, our team can assess the tree and advise on appropriate arboricultural management.

For suspected subsidence, we recommend that concerns about the building itself are also assessed by an appropriately qualified building professional or structural engineer.

Can Trees Cause Subsidence?