How Do I Know If My House Has Subsidence?

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Quick answer

You know your house may have subsidence when you see diagonal cracks wider than about 3mm near doors and windows that show on both the inside and outside of the same wall and keep widening over time — often with sticking doors and sloping floors. But you cannot confirm it yourself: the diagnosis depends on whether the cracks are actively moving. Screen the ground for the address (is it on shrink-swell clay or in a coalfield?), then have a RICS surveyor or structural engineer monitor the movement and classify it. Confirmation almost always needs a period of monitoring.

A step-by-step check

StepWhat to do
1. Look for diagnostic cracksCheck walls near doors and windows for diagonal cracks wider than about 3mm that appear on both the inside and outside of the same wall. These openings are the weakest points and where subsidence cracks usually show first.
2. Test whether the cracks are movingPhotograph and date each crack, or bridge it with a paper tell-tale. Cracks that widen over weeks or months indicate active movement; stable cracks that have not changed for years are usually cosmetic.
3. Check doors, windows and floorsNote any doors or windows that have started to stick or drop out of square, rippling wallpaper, and floors that slope or skirting that has pulled away — secondary signs that support (or weaken) a subsidence read.
4. Screen the ground for the addressCheck whether the property sits on shrink-swell clay or in a coalfield using British Geological Survey (BGS) and Mining Remediation Authority data. If the ground is low-risk, cracking is far more likely to be something else.
5. Get a professional assessmentA RICS Level 2 or Level 3 survey, or a structural engineer's report, classifies the damage against BRE Digest 251 and advises whether monitoring is needed. This is the step that confirms or rules out subsidence.

Why can't I confirm subsidence on my own?

Subsidence is diagnosed by movement over time, not by a single crack. A structural engineer or RICS surveyor rules out other causes — thermal cracking, wall-tie failure, lintel problems and heave (ground swelling upward, often after a tree is removed) — and monitors the cracks, sometimes across a full seasonal cycle because shrink-swell clay moves with the weather. Insurers and lenders act on that professional assessment, classified against the BRE Digest 251 damage scale, not on a homeowner's judgement.

“If you are worried that your property may be suffering from subsidence, contact your buildings insurer, who will be able to arrange for the damage to be assessed.”
— Association of British Insurers, subsidence guidance

How do I check the ground for the address?

The most common cause of subsidence in England and Wales is shrink-swell clay, so the ground beneath the property is the single most useful piece of context. HouseCheckup screens British Geological Survey (BGS) GeoSure data for shrink-swell clay, landslides, compressible ground and dissolution, plus Mining Remediation Authority (formerly the Coal Authority) data for former coal workings. If the ground is low-risk and there is no mining, active subsidence becomes much less likely — and cracking is more likely to have another cause.

What if I'm buying rather than already own the house?

Do the checks before you commit. Ask the seller to disclose known subsidence and any past claims on the TA6 Property Information Form, screen the ground and mining risk for the exact address, and — if you see any signs — commission a RICS Level 3 (full structural) survey or a structural engineer. Because subsidence can stop a mortgage valuation, checking before you offer is far cheaper than discovering it after your survey or, worse, after exchange.

Start with the ground

Before you pay for a structural survey, find out whether the address was ever at risk. HouseCheckup screens BGS GeoSure ground-stability data and coal-mining risk for any England or Wales address, and the £24.99 Complete report sets it alongside 15+ official checks in total — flood and EPC among them — in a single plain-English verdict.

Run the ground-stability checkSee a sample report

Still not sure it's subsidence? Check what the ground under that address is doing.

Symptoms narrow it down; they don't settle it. BGS ground-stability data, the coalfield record and past claims history all sit against one specific property, not a symptom list. Enter the address and the £24.99 Complete report reads them back in plain English alongside 15+ other official checks — worth doing before you spend on a structural survey.

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£24.99 one-off · no subscription · Human-checked and emailed to you. See a sample report

Frequently asked questions

Look for the diagnostic pattern first: diagonal cracks wider than about 3mm near doors and windows, visible on both the inside and outside of the same wall, that are getting wider over time. Add sticking doors, rippling wallpaper and sloping floors as supporting signs. Then screen the ground — is the address on shrink-swell clay or in a coalfield? Finally, confirm with a RICS survey or structural engineer, who will monitor the cracks and classify them against the BRE Digest 251 scale. No single sign proves subsidence; it is the combination plus professional confirmation that does.
You can gather strong evidence yourself — measuring crack width, tracking whether cracks are widening, and checking whether the ground is high-risk clay or former mining. But you cannot confirm subsidence without a professional. A RICS surveyor or structural engineer monitors movement over time and rules out other causes such as thermal cracking, wall-tie failure or heave. Lenders and insurers act on the professional assessment, not a homeowner's judgement.
Because the diagnosis depends on whether cracks are moving, confirming active subsidence usually involves a period of monitoring — often several months and sometimes across a full seasonal cycle, since shrink-swell clay moves with the weather. An initial survey can flag the likelihood quickly, but insurers typically require monitoring data before accepting a claim and agreeing remediation.
No. Subsidence is downward ground movement, often from clay shrinking in dry weather. Heave is the opposite — the ground swelling and pushing the foundations up, for example after a large tree is removed and the clay rehydrates. Settlement is the small, one-off downward movement of a new building or extension as the ground compresses under its weight, and is normally harmless. A structural engineer distinguishes between them, because the fix differs.
Screen the ground and coal-mining risk for the exact address, ask the seller to disclose known subsidence and past claims on the TA6 form, and commission a RICS Level 3 (full structural) survey or a structural engineer if signs are present. Confirm the property is insurable and at what excess. Subsidence can stop a mortgage valuation, so doing the ground and structural checks before you offer protects you from committing to a home that cannot be financed.

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Sources

HouseCheckup provides area-level ground screening, not a structural diagnosis. Only a RICS survey or structural engineer can confirm subsidence at a specific property.