Signs of Subsidence in a House
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Quick answer
The classic signs of subsidence in a house are diagonal cracks wider than about 3mm near the corners of doors and windows, cracks that are visible on both the inside and outside of the same wall, doors and windows that stick, rippling wallpaper and sloping floors. The tell-tale difference from harmless settlement is that subsidence cracks keep widening over time. Because most UK subsidence is caused by shrink-swell clay (British Geological Survey data), the surest first step is to check the ground beneath the specific address before assuming a crack is cosmetic.
What subsidence looks like: signs inside and outside
No single sign proves subsidence — surveyors look for a pattern. The table below describes each common sign, what it actually looks like, and how much weight to give it.
| Sign | What it looks like | Concern |
|---|---|---|
| Diagonal cracks near doors and windows | Cracks running at roughly 45°, usually starting at the corner of a door or window opening (the weakest point in a wall). Subsidence cracks are typically wider than 3mm, wider at the top than the bottom, and visible on both the inside and outside of the same wall. | High |
| Cracks that appear suddenly and keep widening | New cracks that open up over weeks or months, rather than fine hairline cracks that have been stable for years. Progressive movement is the single strongest signal that ground movement is active. | High |
| Doors and windows sticking or jamming | Doors and windows that catch, drop or no longer close squarely, because the frame has been pulled out of square by foundation movement. Often noticed alongside cracking above the same opening. | Medium |
| Wallpaper wrinkling or rippling at wall/ceiling joints | Creasing or rippling of wallpaper where it is not caused by damp — commonly at the junction between wall and ceiling as the structure distorts. | Medium |
| Sloping or uneven floors | Floors that noticeably slope, or skirting boards that have pulled away from the wall, indicating part of the structure has dropped. | Medium |
| Gaps around extensions, bay windows or porches | Cracks or gaps where a newer, more lightly founded structure meets the main house — a common place for differential movement to show first. | Watch |
Concern is indicative only. Any crack wider than about 3mm, or any crack that is growing, warrants a professional opinion.
How do I tell subsidence from normal settlement?
Almost every house has some cracks. The ones that matter are diagonal, wider than roughly 3mm, positioned near door and window openings, visible on both faces of the wall, and — above all — getting wider. Surveyors grade cracking against BRE Digest 251, the Building Research Establishment's standard damage-classification scale, where cracks under about 1mm are “negligible” and cracks above 5mm start to signal structural movement. Stable hairline cracks and straight cracks along a plaster join are usually cosmetic.
“Not all cracks are a sign of subsidence. Many are simply the result of normal movement, such as the expansion and contraction of building materials.”
Why is shrink-swell clay the usual cause?
The dominant cause of subsidence in England and Wales is shrink-swell clay: clay-rich soils that swell when wet and shrink in dry spells, moving the foundations they support. The British Geological Survey describes shrink-swell as one of the most damaging geohazards in Britain, and its GeoSure mapping shows large parts of London, the South East and East Anglia sit on high-susceptibility clay. Hot, dry summers make it worse — which is why the ABI reports subsidence claims spiking in drought years. Nearby trees drawing moisture from clay soil are a frequent aggravating factor.
What should I do if I spot these signs?
If you already own the home and cracks are actively widening, contact your buildings insurer — subsidence is a standard peril on most policies, and the insurer will usually arrange monitoring. If you are buying, do the checks before you commit: screen the ground and coal-mining risk for the exact address, then have a RICS Level 2 or Level 3 survey, or a structural engineer, assess whether any cracking is progressive. Subsidence can stop a mortgage valuation, so it is far cheaper to check the ground before you offer than to discover it after your survey.
Where to check and how to verify
| Step | Where to check |
|---|---|
| Screen the ground beneath the property | Check whether the address sits on shrink-swell clay or other unstable ground before you assume a crack is cosmetic. HouseCheckup screens British Geological Survey (BGS) GeoSure data — the ground-stability check by postcode. |
| Check for former coal mining | In a coalfield, ground movement can come from old workings. The Mining Remediation Authority (formerly the Coal Authority) issues the definitive coal mining report (CON29M) via GOV.UK. |
| Commission a professional opinion on active cracks | A RICS Level 2 or Level 3 survey, or a structural engineer's report, assesses whether cracking is progressive. Surveyors classify damage against BRE Digest 251, the standard crack-severity scale. |
| Ask the seller and check insurance history | The TA6 Property Information Form asks the seller to declare known subsidence and any past claims. A previous subsidence claim can affect future insurance, so the Association of British Insurers (ABI) advises buyers to check the property's history. |
Check the ground before you offer
A crack tells you movement may be happening; the ground data tells you whether the address was ever at risk in the first place. HouseCheckup screens BGS GeoSure ground-stability data and coal-mining risk for any England or Wales address, then the £24.99 Complete report combines it with flood, EPC and 15+ further official checks in one plain-English verdict.
Seen cracks you're not sure about? Check the property itself.
A signs checklist can only take you so far — whether this house is at risk depends on the ground under it, and that's a property-level question. Enter the address and the £24.99 Complete report reads BGS ground-stability and coal-mining data for that exact home, plus 15+ other official checks, in plain English.
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Frequently asked questions
Related guides
Sources
- GeoSure — ground stability data — British Geological Survey (BGS)
- Shrink–swell: the most damaging geohazard in Britain — British Geological Survey (BGS)
- Subsidence — advice for homeowners — Association of British Insurers (ABI)
- Home surveys — levels and what they cover — RICS
- Get a coal mining report — Mining Remediation Authority / GOV.UK
HouseCheckup screens area-level official data to flag risk; it is not a structural survey and cannot confirm subsidence at a specific property. Where signs are present, commission a RICS survey or structural engineer.