What is subsidence?

Published 22 June 2026

• Cracks in the walls, which are the most noticeable indicators of subsidence.
• Wallpaper that’s ripped without any signs of dampness.
• Doors and windows that don't close properly, stick unexpectedly, or close easily in winter but not in summer.
• Diagonal cracks near windows or doors, inside or outside, especially if they vary in width.
• Floors that appear to be sinking.

Subsidence is the downward movement of the ground beneath a building's foundations, where the movement isn't caused by the weight of the building itself. It's one of those problems that can feel overwhelming, but understanding what to look for and how to respond makes all the difference.

In this guide, we'll walk you through how to spot the warning signs in your home, what causes subsidence in the first place, and the steps you can take to prevent it. We'll also cover repair options, how subsidence insurance works, and what to do if you need to make a claim or sell your property during the process.

Subsidence is the downward movement of the ground beneath a building's foundations, where the movement isn't caused by the weight of the building itself. Instead, it happens when the soil underneath becomes unstable.

It's worth knowing that subsidence is just one type of ground movement. Heave is the opposite – when the ground moves upwards, Landslip happens when ground moves down a slope, taking the property with it. In the UK, subsidence is more common after hot weather and prolonged dry spells, when clay soil shrinks and loses its ability to support your home's foundations properly.

Cracks are the most obvious sign that something might be going on with your home's foundations. But here's the thing – not every crack means you've got subsidence problems. Some are just cosmetic, caused by plaster shrinkage or normal settlement.

So, what should you actually look out for?

Pay close attention to diagonal cracks that form around windows and doors. These are usually wider at the top than the bottom and can appear both inside and outside your home. They often follow the mortar lines in a stepped pattern and may extend past the damp proof course down to the foundations. These types of cracks tend to show up after long periods of dry weather.

Here's a practical tip – if a crack is wider than a 10p coin (about 3mm), it's worth getting a structural engineer to take a look. This simple test can help you decide whether professional advice is needed.

Other warning signs include:

• Wallpaper that's ripped without any signs of dampness.
• Doors and windows that don't close properly, stick unexpectedly, close easily in winter but not in summer.
• Floors that appear to be sinking.
• Cracks that vary in width or seem to be getting worse over time.

If you spot any of these signs, don't panic. It doesn't automatically mean subsidence, but it's sensible to investigate further. For more detailed guidance on what to watch for, download our subsidence signs guide.

Subsidence happens when the ground beneath a building sinks or shifts downward. There are four main causes to be aware of.

Trees and vegetation – large trees with high water demand can draw hundreds of litres of moisture from the soil each day. Over a long period of time, tree roots can dry out the ground, especially on clay soils, causing it to shrink and lose volume beneath your foundations.

Clay soil shrinkage – clay soils act like a sponge, swelling when wet and shrinking when dry. During prolonged dry spells, particularly in hot summers, clay loses moisture and contracts. In extreme cases, this causes the ground to sink, especially in areas like London and the South East where clay soil is common.

Leaking drains – cracked or damaged pipes can wash away the subsoil below your foundations. As water escapes, it erodes the ground, creating voids that lead to settlement and subsidence.

Mining activity – although less common, historic mining operations can leave underground cavities that eventually collapse, causing the ground above to sink.

Each of these causes can affect your property differently, but they all share one thing in common – they weaken the ground your home sits on.

Although there isn't much you can do about the soil type underneath your house, there are steps you can take to reduce the risk of subsidence and avoid the need to underpin your house. Some properties are more prone to subsidence depending on soil type and location – clay soils, particularly in areas like London and the South East, are especially vulnerable to ground movement.

• Regularly prune trees and large shrubs near your house, like wisteria. Trees with high water needs can dry the soil up to the same height of the tree.
  
  
• For large, established trees, hire professional tree surgeons to help manage their growth. Managing or removing mature trees near your property is often the first step in tackling subsidence. This can help avoid cutting the tree down in the future.
  
  
• Check water pipes and gutters regularly to ensure they're not blocked or leaking. This is especially important for older homes where tree roots might grow through old clay pipes.
  
  
• Improve drainage around your home by replacing concrete or tarmac driveways and patios with more porous materials, such as gravel or grass.
  
  
• Check garden walls and extensions for early signs of movement, such as small cracks or leaning. Catching these warning signs early can prevent more serious structural issues developing.

Once subsidence has been confirmed, there are several repair options available depending on the severity and cause of the damage.

Tree management

Managing or removing mature trees near your property is often the first step in tackling subsidence. Trees with high water demands can dry out clay soil, causing the ground beneath your foundations to shift. In some cases, pruning or reducing the canopy can be enough to stabilise the soil. In more severe situations, complete removal may be necessary to prevent further damage.

However, it's worth noting that removing a large tree can sometimes lead to heave (where the ground swells as moisture levels increase), so always consult a structural engineer or tree specialist before taking action.

Wall ties and pipe repairs

Two straightforward repairs can make a real difference to buildings affected by subsidence. Wall ties can be installed between the inner and outer walls to strengthen the structure and prevent further movement. Meanwhile, repairing damaged or leaking pipes is essential, as waterlogged soil can wash away the ground beneath your foundations, making subsidence worse.

Both of these methods are relatively simple fixes and are often carried out early in the repair process.

Underpinning

Underpinning is typically used as a last resort when foundations need serious reinforcement. This process involves strengthening the existing foundations by extending them deeper into stable ground, often using mass concrete or modern resin injection techniques. It's a more invasive and costly solution, but it's sometimes the only way to stabilise a property with a history of subsidence.

For more details on underpinning, check out our article on underpinning.

In rare and extreme cases, reconstruction may be required where the existing structure simply cannot be repaired safely.

Your Allianz Online Home Insurance covers subsidence and heave for your property, so there's no need to seek specialist cover.

Only a small number of houses actually suffer from subsidence, and some new homes may go through a phase known as 'settlement,' which is different from subsidence but can have some similar symptoms. Settlement occurs when the weight of the house settles into the foundations during the first few years and might cause some cracks in the plasterwork. If you're worried, there's no harm in getting a professional opinion.

Buildings insurance typically covers damage to the structure of your home caused by subsidence, heave and landslip. This includes repair costs to your property's foundations, walls and outbuildings when they're damaged at the same time by the same cause.

Contents insurance doesn't usually cover damage to your belongings caused by subsidence. Your buildings policy focuses on the structural repairs needed to stabilise and restore your home.

Most standard home insurance policies include subsidence cover, so specialist policies aren't usually necessary. Your Allianz Online Home Insurance covers subsidence and heave as standard, giving you protection without the need for additional cover.

However, properties with a history of subsidence may face higher premiums or larger excess amounts. In some cases, insurers may require you to work with a specialist broker to arrange cover. If you've had previous subsidence issues and want to switch providers, the British Insurance Brokers' Association can connect you with specialists who understand complex subsidence risks.

Settlement happens when a new building's weight compresses the ground beneath it during the first few years. It's a natural process that causes minor cosmetic cracks as the soil adjusts to the load. In most cases, settlement is harmless and stops once the building has been standing for about five years.

Subsidence can happen at any time. It's ongoing ground movement caused by external factors like clay soil shrinking in dry weather, tree roots drawing moisture from the soil, or leaking drains washing away the subsoil. Another type of ground movement is landslip, where the ground moves sideways down a slope. Heave is the opposite of subsidence – it's when the ground moves upwards, often after trees are removed and moisture builds up in the soil.