Clay soil shrinkage
This is the single biggest cause of subsidence in the UK. Clay soil is "cohesive," meaning it behaves like a plasticine or a sponge. It swells in volume when it gets wet and shrinks dramatically when it dries out. During long, dry summers or periods of drought, the clay soil beneath a house can lose a significant amount of moisture and shrink. This loss of volume causes the ground to sink, taking the foundations with it. This is often worse on one side of a house (e.g., the sunny, south-facing side), leading directly to differential settlement.
The influence of trees and large shrubs
Trees and shrubs act like giant straws, drawing enormous amounts of water out of the soil. A large, mature tree can absorb thousands of gallons of water a year.
If a thirsty tree (like an oak, willow, or poplar) is located close to your property, its roots can extend under your foundations and draw moisture from the clay soil, causing it to shrink in a very localised area.
This is a primary driver of differential settlement, as the ground near the tree sinks while the ground further away does not.
Water damage from leaking drains
The opposite problem can also cause subsidence. If a drainpipe or water main under the ground cracks or breaks, the escaping water can wash away or erode finer, granular soil particles (like sand and silt).
This process, known as "washout," gradually creates a void or a very soft, weak spot in the ground. When the soil supporting the foundation is washed away, that section of the foundation can collapse into the weakened area, causing a sudden settlement.
Soil type and poor ground conditions
While clay soil is the main issue, other soil types can also pose a risk. Granular soils like sand or gravel can be washed away or can settle if the ground was not properly compacted when the house was built.
This is a particular risk for newer extensions or properties built on "made ground" or backfill, as this material can compress and settle over many years under the immense weight of the building.
Clay Soil Shrinkage
This is the single biggest cause of subsidence in the UK, especially in the South East. Clay soil shrinks and loses volume when it dries out, causing the ground to sink. Prolonged dry spells or hot summers can make clay soil subsidence much worse.
Tree Roots
Large trees and shrubs are thirsty. Their roots can draw huge amounts of moisture from clay soil, causing it to shrink dramatically. The risk increases with the tree's size and proximity to your home. Poplars, willows, and oaks are known for having extensive root systems, so subsidence tree distance is a key factor.
Leaking Drains and Water Pipes
Slow, steady leaks from broken drains can wash away or soften the soil under your foundations, weakening the ground until it can no longer support the weight of your home. This is a common but often overlooked cause of subsidence.
Poor Ground Conditions
Sometimes, the ground may not have been properly prepared when the house was built, or it could be affected by historical issues like old mining works in the area.
Diagonal cracks
These are the classic sign. Look for diagonal cracks in walls, often appearing around doors and windows. They are usually wider at the top than the bottom and are visible both inside and outside.
Sticking doors and windows
When a building moves, it can warp the frames around your doors and windows, causing them to stick or not close properly.
Rippling wallpaper
If you see creasing or tearing in your wallpaper that isn't caused by damp, it could be a sign that the wall behind it is moving.
Gaps appearing
Look for gaps where your extension meets the main house, or where the skirting boards are coming away from the floor.
Sloping floors
A noticeable slant in your floors is a clear indicator that the structure is moving.
Sloping floors
A noticeable slant in your floors is a clear indicator that the structure is moving.
Diagonal Cracks
These are the classic sign. Look for diagonal cracks in walls, often appearing around doors and windows. They are usually wider at the top than the bottom and are visible both inside and outside.
Sticking Doors and Windows
When a building moves, it can warp the frames around your doors and windows, causing them to stick or not close properly.
Rippling Wallpaper
If you see creasing or tearing in your wallpaper that isn't caused by damp, it could be a sign that the wall behind it is moving.
Gaps Appearing
Look for gaps where your extension meets the main house, or where the skirting boards are coming away from the floor.
Sloping Floors
A noticeable slant in your floors is a clear indicator that the structure is moving.
Worried about the signs?
Find out what's happening beneath your home
The most important first step is to understand the root cause of the problem. Our team can help you make sense of the signs you're seeing. Arrange a no-obligation video consultation, where we can make an initial assessment and clearly explain your options.
