“Subsidence” is one of the most frightening words in a survey report, and one of the most misused. Plenty of cracks get called subsidence when they’re nothing of the kind, and occasionally genuine subsidence gets dismissed as “settlement”. Here’s what the word actually means, what causes it, and how to tell whether you should be concerned.
What subsidence actually is
Subsidence is the downward movement of the ground supporting a building’s foundations, causing the building to move with it. The important part of that definition is the ground: subsidence is caused by something happening to the soil or rock beneath the foundations, not by the building itself.
It’s worth separating it from three related terms insurers and surveyors use:
- Settlement — the natural compaction of ground under a new building’s weight, usually in its first few years. It generally stabilises and is normally not covered by insurance.
- Heave — the ground moving upward, often when clay soil swells after a tree is removed or as it rewets.
- Landslip — ground moving down a slope.
What causes subsidence
The main causes in the UK are:
- Clay shrinkage. Clay soils shrink when they dry out and swell when they rewet. Long dry summers, and particularly trees and large shrubs drawing water from the soil near foundations, are the classic trigger. Shallow foundations on clay are the most vulnerable.
- Leaking drains. A broken or leaking drain can wash fine material out of the ground or soften it, so the foundation loses support. This is a common cause on non-clay soils and is often overlooked.
- Mining. Across much of Yorkshire and the North, historic coal and other mineral workings sit beneath towns and villages. Collapse of old shallow workings can cause movement at the surface. A coal mining report from the Mining Remediation Authority (formerly the Coal Authority), which conveyancers order in affected areas, is designed to flag this.
- Poor or made ground. Buildings on backfilled land, old quarries, or poorly compacted ground can move as it consolidates.
- Water courses and changes in ground water. Streams, springs and changes in drainage can wash out or soften supporting ground.
Signs of subsidence in a house
Subsidence cracks tend to share characteristics that distinguish them from ordinary cracking:
- Diagonal cracks, often starting at the corners of doors and windows, that are wider at one end than the other.
- Cracks visible both inside and out at the same location.
- Cracks wider than a few millimetres, or that are getting wider over time.
- Doors and windows sticking or jamming as their openings distort.
- Wallpaper rippling or tearing at the junction of walls and ceilings, not caused by damp.
- Gaps opening where an extension or bay meets the main house.
Not every crack is subsidence. Most are thermal movement, drying shrinkage in plaster, or long-stable historic movement. Our guide to what actually causes cracks in walls explains how to read a crack properly.
How to check for subsidence
If you’re worried about a crack:
- Photograph it with a ruler alongside, and note the date.
- Monitor it. Mark the ends with a pencil and date them, or fit a simple tell-tale gauge. What matters most is whether it’s changing — getting wider or longer — over weeks and months, including across seasons.
- Look at the pattern. Is it tapered? Does it follow a line from a door or window? Is it visible on both faces of the wall?
- Look for a cause. Trees within influencing distance, a leaking gutter or gully, damp ground at the base of the wall, or signs of drain problems.
- Get a professional assessment if the crack is wide, growing, tapered, or accompanied by sticking doors and windows.
Our cracks in walls checker shows where a crack sits on the BRE Digest 251 damage scale that surveyors, engineers and insurers use, and what its pattern usually means.
What to do if you think it’s subsidence
If you own the property, contact your buildings insurer early. Most policies cover subsidence, and insurers usually manage the investigation. We explain what the insurance typically covers and how subsidence claims actually work in separate guides.
If you’re buying, don’t guess. A crack can be decades old and stable, or active and serious, and the report should tell you which, and what to ask the seller. Where there’s a specific concern, a subsidence assessment focuses on cause and whether movement is ongoing — and the good news is that most subsidence can be fixed without underpinning. Get in touch with the address and a photo of what you’re seeing.
Sources and further reading
- Assessing cracks in houses — BRE
- BRE Digest 251: Assessment of damage in low-rise buildings — BRE
- Mining reports — Mining Remediation Authority (formerly the Coal Authority)
- Access coal mining information and data — GOV.UK