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.
Tree root influence
Roots from trees and large shrubs that are in the vicinity of a property have the ability to grow down into the ground and then spread out. Often, this means that roots from trees and shrubs can work their way under your property’s foundations in search of moisture. A large, mature tree can absorb between 10 and 150 gallons of water every single day, which is extracted from the ground. As moisture is drawn out, the soil will compact, causing it to shrink in a localised area. This is a common cause of subsidence that results in uneven ground movement.
Leaking drains
Deteriorating or broken underground pipework can allow water to seep into the ground. This excess water can wash away granular soil particles (like sand and silt) and erode the sub-surface, or it can cause other soils to expand, resulting in ground movement. In weaker ground, this can even cause sudden settlement and form voids.
Poor ground conditions
While clay is a common culprit, other soil types pose a risk too. Granular soils, like sand or gravel, can settle or be washed away, particularly if the ground wasn't properly compacted when an extension or new build was initially constructed. The weight of the building can cause these soils to compress and settle over time.
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
Cracks that run diagonally or zig-zag across brickwork are classic signs of subsidence. These typically appear around doors and windows, are often visible both inside and outside the property, and are wider at the top than the bottom, measuring at least 3mm wide. (Remember that hairline cracks, which are very thin and run vertically or horizontally, are generally harmless and stop progressing after a couple of years).
Sticking doors and windows
When the structure and foundations move, it can warp door and window frames. This may make them difficult to close, or they might even become jammed shut.
Rippling wallpaper
If your wallpaper is rippling, creasing, or tearing without any sign of damp, it could be a sign that the wall behind it is moving due to subsidence.
Gaps appearing
Look for gaps around doors, windows, and extensions, or between the wall and skirting boards or architraves. These gaps are a sign that movement is happening.
Sloping floors
Floors that feel sloping, uneven, or spongy, or where you notice a visible lean or slant, can be a sign of subsidence.
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.
