Subsidence Risk Check
How to check subsidence risk before buying a house
Subsidence is the most expensive single defect a UK home buyer can inherit. Active movement can cost £15,000-£40,000 to remediate, sit on insurance records for the life of the property, and reduce resale value by 5-15% even after works. Most of the decision-making data is free and public.
Last updated: 6 May 2026. Editorially reviewed: 20 May 2026.
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Check subsidence signals for a UK address in 15 seconds
BGS clay susceptibility, building age, tree context and the things to ask your surveyor.
Run a free previewWhat causes subsidence
Subsidence is downward movement of the ground supporting a building's foundations. UK subsidence has three main drivers, often in combination:
Clay soil shrink-swell
Clay soils expand when wet and contract when dry. In hot, dry summers the contraction drops foundations unevenly. London clay, Oxford clay, and Gault clay across the South and East are the highest-risk geologies. Insurance industry claims spike during dry years.
Tree root influence
Trees within their mature height of the building, on clay soil, draw water from the soil under foundations and amplify shrinkage. Oak, willow, and poplar are the worst offenders. Tree Preservation Orders complicate removal.
Drainage failure and ground washout
Leaking drains undermine foundations by washing fine soil out from under them. Often misdiagnosed as clay subsidence; a CCTV drain survey reveals it.
How to check BGS clay risk by postcode
The British Geological Survey publishes shrink-swell susceptibility data for the UK. Postcode-level lookups are available through the BGS GeoIndex and through commercial environmental searches.
- 1Open the BGS GeoIndex at bgs.ac.uk/map-viewers/geoindex-onshore and zoom to the postcode. Toggle the "Shrink-Swell" layer.
- 2Read the susceptibility band: A/B (low), C (moderate), D/E (high). High-band postcodes warrant viewing red-flag attention and possibly a structural engineer pre-survey.
- 3Cross-reference with mature trees in proximity: a high BGS band plus oaks within 20m of the building is the highest-risk combination.
The full conveyancing environmental search (Landmark, Future Climate Info) bundles BGS data with mining, contaminated land, and flood. It costs £40-£70 and is part of the standard search pack.
Signs to look for at a viewing
Most surveyors will pick these up; spotting them at the viewing lets you decide whether to commission a Level 3 survey or walk before paying for one.
| Red flag | What it suggests |
|---|---|
| Stepped diagonal cracks wider than 3mm | Especially around openings (windows, doors). Hairline cracks are usually thermal/cosmetic. |
| Doors and windows that stick or are out of square | Frames distorting suggests the building is moving. |
| Gaps between extensions and the main wall | Differential foundation depths cause separate settlement; very common on Victorian extensions. |
| Sloping or unlevel floors | Particularly in older houses; combine with crack patterns. |
| Visible cracking that continues from inside to outside through the same wall | Indicates structural rather than plaster movement. |
| Mature trees within their height of the building on clay soil | Trees draw moisture from clay; shrinkage drops the foundation underneath. |
| Ripped wallpaper around door frames or in corners | Often hides recent crack patterns sellers have papered over. |
How subsidence affects insurance and mortgage
Subsidence has the longest tail of any property defect on insurance: a single claim sits on insurance industry databases for the lifetime of the property. Three scenarios:
No history, high BGS susceptibility
Standard insurance available from mainstream insurers. Some load premiums modestly; most don't. Standard mortgage with no retention.
Historic claim, remediated, stable
Specialist insurer placement is common; mainstream insurers may quote with higher excesses (£1,000-£2,500 specifically for subsidence vs typical £100-£250). Mortgage accepts with structural engineer's report confirming stability.
Active or recent claim
Insurance is restricted to specialist insurers, often with high excesses and premium uplift. Lenders impose retentions or refuse outright until remediation is complete and warrantied.
What a subsidence survey involves
If your Level 2 or Level 3 surveyor flags movement, the standard next step is a structural engineer's assessment. Three typical paths:
- 1Visual structural engineer's report (£400-£900). Engineer inspects, classifies cracks against BRE Digest 251 categories, and gives a written opinion on cause and stability. Sufficient for many lender purposes.
- 2Level monitoring (£500-£1,500 over 6-12 months). Crack-monitor tell-tales or precision levelling installed and re-read; the gold-standard for proving movement is historic and stable.
- 3Trial pits / borehole investigation (£1,500-£5,000). Excavation near foundations to confirm depth, soil type, and any drainage issue. Required before any underpinning design.
Underpinning itself, if recommended, runs £8,000-£20,000 per affected bay; full underpinning of a typical semi can exceed £40,000.
How to negotiate if subsidence is flagged
The negotiating position depends entirely on which of the three scenarios above applies. Use the engineer's report, not the surveyor's, as the basis.
- Historic + stable, documented: 1-3% off price for cosmetic remediation; full insurance/mortgage transferability.
- Historic but undocumented, BGS high: 3-7% off, plus seller funding the engineer's report and any monitoring before exchange.
- Active or recent movement: 10-20% off plus seller-funded remediation to completion; otherwise walk away.
Always ask the seller for the last 5 years of buildings insurance claim history via the TA6 form. Insurers will see it regardless, and disclosure is required by the contract.
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MyPropertyScan combines BGS shrink-swell susceptibility, building age, and known risk factors into a single buyer report. Free preview in 15 seconds.
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Check subsidence signals for a UK address in 15 seconds
BGS clay susceptibility, building age, tree context and the things to ask your surveyor.
Run a free previewFrequently asked questions
How do I know if a house has subsidence?
Three signals to combine: BGS shrink-swell clay susceptibility for the postcode, the property's insurance claim history (ask the seller's solicitor for the buildings insurance record), and visible signs at the viewing. Stepped diagonal cracks wider than 3mm, doors and windows out of square, and gaps between extensions and main walls are the classic visible red flags.
Does subsidence affect getting a mortgage?
Active subsidence usually triggers a lender retention until a structural engineer's report and remediation plan are in place. Historic, stable movement that has been monitored is typically accepted at standard terms. If the property has been underpinned, lenders accept the property with documentation but may require specialist insurance.
How much does subsidence devalue a property?
A history of subsidence claims typically reduces market value by 5-15% even after remediation, with the lower end on properties where works are documented and warrantied, and the higher end where the cause was clay-driven and trees remain in proximity. Insurance premiums also load by 20-100% relative to the local average for the lifetime of the property's claim history.
What is clay soil shrinkage risk?
Clay soils expand when wet and shrink when dry. In dry summers the shrinkage causes foundations to drop unevenly, and trees within their mature height of the building accelerate the effect by drawing water from the soil. The British Geological Survey publishes shrink-swell susceptibility maps for the UK; London clay, Oxford clay, and Gault clay are the highest-risk geologies.
Is subsidence a reason to pull out?
Active progressive movement confirmed by a structural engineer is usually a reason to walk away unless the seller funds full remediation before exchange. Historic, stable movement with documentation and ongoing insurability is normally a renegotiation rather than a deal-breaker. The structural engineer's report is the document that decides which category the property falls into.
Keep going
Related guides
- House buying checklist , the full pre-offer checklist of every property check to run.
- Bad house survey: what to do , renegotiate, pull out, or proceed when the survey flags movement.
- Subsidence monitoring on a survey , what surveyors mean by monitoring and what it commits you to.
- Flood risk when buying a house , the other major environmental risk you should check before offering.
Editorial review
Editorial owner: BiteRight Ltd, operator of MyPropertyScan. We review buyer guides against UK public property datasets, RICS survey wording, lender requirements, and common buyer questions.
Pages are updated when source coverage, property-risk guidance, survey cost assumptions, or product checks materially change. Methodology and dataset limitations are explained on the MyPropertyScan methodology page.
Sources used
We use UK public and specialist sources where they are available. Public datasets can be incomplete, delayed, or missing for some addresses. Treat them as a starting point, not as a replacement for professional advice.
Source standard: preference goes to official government datasets, statutory bodies, professional standards, and primary dataset publishers. We cite the source family on the page and explain coverage limits rather than filling gaps with unsupported estimates.