What Is Subsidence and How Does It Affect Homes in Manchester?
Understanding subsidence is the first step to protecting your property and getting the right help.
What subsidence means for your property
Subsidence is the downward movement of the ground beneath a building's foundations. When the soil supporting your home shrinks, settles, or washes away, it causes the foundations to sink unevenly. This uneven movement puts stress on the structure above, leading to cracks, distortion, and potentially serious structural damage.
In Manchester and Greater Manchester, subsidence is particularly common due to our clay soils, mature trees, and the age of much of our housing stock. Victorian and Edwardian properties with shallow foundations are especially vulnerable.
Common causes in the UK
Clay shrink–swell
Clay soils expand when wet and shrink when dry. During hot, dry summers, clay can shrink significantly, causing the ground to drop and foundations to move. This is the leading cause of subsidence in Manchester.
Tree roots
Large trees near properties draw moisture from clay soil, causing it to shrink. Species like oak, willow, poplar, and ash are particularly problematic. Even trees on neighbouring properties can affect your home.
Leaking drains
Broken or leaking drains can wash away soil supporting foundations, causing localised subsidence. Older properties with clay or cast-iron drains are particularly at risk.
Old mining and voids
Parts of Greater Manchester have historic coal mining or limestone workings beneath. Old mine shafts or voids can collapse, though this is less common than clay-related movement.
Subsidence vs settlement vs heave
Subsidence
Downward movement caused by the ground beneath foundations sinking or being removed. This is an ongoing process that gets progressively worse without intervention.
Settlement
Normal downward movement as a new building compresses the soil beneath it. Settlement typically occurs in the first few years after construction and then stabilises. Minor settlement cracks are usually cosmetic and don't require major repairs.
Heave
Upward movement of the ground, often caused by clay soil expanding after tree removal. When a large tree is removed, the soil it was drying out can rehydrate and swell, pushing foundations upward.
Why Manchester and Greater Manchester see subsidence cases
Manchester sits on predominantly clay soil, particularly Mercia Mudstone, which is highly reactive to moisture changes. When we experience hot, dry summers (increasingly common with climate change), the clay shrinks significantly. When it rains heavily in winter, the clay expands.
The combination of clay soil, mature tree-lined streets, aging drainage systems, and Victorian/Edwardian housing with shallow foundations creates the perfect conditions for subsidence. Areas like Didsbury, Chorlton, Altrincham, and Prestwich—with their large period properties and established trees—see higher rates of subsidence claims.
When to move from worry to action
Not every crack means subsidence, but certain signs warrant professional investigation:
- • Cracks wider than 3mm (about the width of a 10p coin)
- • Cracks that are getting wider or longer
- • Diagonal cracks running from corners of windows or doors
- • Doors and windows that stick or won't close properly
- • Visible gaps between walls and ceilings or floors
- • Sloping or uneven floors
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