Ground Stability Search: What It Checks and Why It Matters

When a buyer's solicitor orders the standard property search pack, one of the categories they will check is ground stability. This assessment looks at the geology beneath your property and the surrounding area to identify risks that could cause structural damage over time — things like subsidence from clay shrinkage, landslip on sloping ground, or voids left by dissolved rock.

As a seller, you will not usually see the ground stability results yourself — they go to the buyer's solicitor. But any flags in the report will generate enquiries that you need to answer. Knowing what the search checks and what the results mean puts you in a much stronger position to respond quickly and keep your sale on track.

What a ground stability search checks

A ground stability search is an electronic report compiled from geological data held by the British Geological Survey (BGS), the Coal Authority, and other public and commercial sources. It assesses several categories of ground risk, each of which can affect a building's foundations and structural integrity. The main risk categories are set out in the table below.

Each risk category is assessed independently and given its own result. A property might pass on landslip but receive an amber flag for clay shrinkage. The search provider compiles these results into a report, typically 10 to 30 pages long, that includes maps showing the underlying geology and the assessed risk level for each category.

How ground stability is assessed

Ground stability searches are desktop exercises. No one visits the property or takes soil samples. Instead, the search provider overlays the property's location onto geological mapping data from the BGS, which has surveyed the bedrock and superficial geology of England and Wales in detail over more than 180 years.

The BGS's GeoSure dataset is the primary source for most residential ground stability assessments. GeoSure classifies the land into risk bands (typically A to E, where A is negligible and E is very high) for each hazard type. The search provider translates these risk bands into their own reporting format — usually a traffic-light system of green, amber, and red.

It is important to understand what a ground stability search does not do. It does not examine the property's actual foundations, check for existing structural damage, or confirm whether subsidence has occurred. It tells you what the geology is capable of, not what it has actually done to the building. If the geological risk is flagged and there are visible signs of damage, a physical survey by a structural engineer is the appropriate next step.

Reading the results: pass, further action, and fail

Like environmental search results, ground stability findings are presented using a traffic-light system. The terminology varies slightly between providers, but the three outcomes are broadly consistent.

Pass (green)

A green result means the BGS data does not indicate a significant geological risk for that category at the property's location. The vast majority of residential properties in England and Wales will receive a green result for most ground stability categories. No further action is required from the seller or the buyer.

Further action (amber)

An amber result means the data shows a moderate or potential risk that may warrant further investigation. This is the most common non-green result for ground stability, and it is particularly frequent for clay shrinkage in the southern half of England. An amber flag does not mean the property has a problem — it means the underlying geology has characteristics that could, in certain conditions, affect buildings.

When the buyer's solicitor sees an amber flag, they will typically raise an enquiry asking whether the property has any history of subsidence or structural movement. As a seller, if you can confirm that no subsidence claims have been made and no cracking is present, the matter is usually resolved quickly. If you are unsure how to respond to enquiries raised by search results, our guide on what to do if searches reveal problems walks through the options.

Fail (red)

A red result means the data has identified a significant geological risk that requires professional assessment before the transaction should proceed. Examples include a property located directly above known natural cavities in soluble rock, within an active landslip zone, or on a site with documented man-made mining voids.

A red result does not automatically prevent the sale. It means the buyer's solicitor and mortgage lender will need additional reassurance — usually in the form of a specialist geotechnical report, a structural survey, or indemnity insurance — before they are satisfied that the risk is manageable.

Clay shrinkage: the most common ground stability flag

Clay shrinkage is by far the most frequently flagged ground risk on residential property searches in England and Wales. According to the British Geological Survey, approximately 43% of the land area in England and Wales is underlain by soils with some degree of shrink-swell potential. In parts of London, the Home Counties, and the Midlands, almost every property search will return an amber flag for this category.

The mechanism is straightforward. Clay-rich soils contain water. During prolonged dry weather, the clay loses moisture and shrinks. When it rains, the clay absorbs water and swells. This cyclical movement puts stress on foundations and can cause cracking in walls, particularly in older properties with shallow strip foundations. Modern buildings constructed since the 1990s are typically designed with deeper foundations specifically to account for clay shrinkage.

Trees near buildings can make clay shrinkage worse. Large trees draw significant amounts of water from the soil through their roots, accelerating the drying process during summer. The Association of British Insurers has identified tree root-related clay shrinkage as one of the most common causes of domestic subsidence claims in the UK.

As a seller, if your property is on clay soil, you should expect an amber flag on the ground stability section of the buyer's environmental search. This alone is unlikely to cause problems. However, if your property has a history of subsidence, or if there are visible cracks wider than 3mm, the buyer's solicitor and surveyor will want to investigate further. Being upfront about any known issues on your TA6 form will help avoid delays later. Section 7.4 of the TA6 asks whether you are aware of any subsidence, landslip, or ground heave, and honest disclosure here is essential.

Landslip, natural cavities, and other serious risks

Landslip

Landslip (also called landslide) risk is assessed based on the slope angle, geology, and drainage characteristics of the land. Properties on or near steep slopes, particularly those with clay or weak rock layers, are most at risk. Coastal properties can also be affected by cliff erosion and retreat.

A landslip flag on a ground stability search does not mean the land is actively moving. It means the geological conditions and terrain are such that movement is possible. If this risk is flagged at amber or red, the buyer's solicitor may request a geotechnical desk study or a site investigation to assess whether the slope is stable. In some cases, indemnity insurance may be available to cover the risk.

Natural cavities and dissolution

Natural cavities form when soluble rocks — primarily chalk, limestone, and gypsum — are dissolved by groundwater over geological timescales. This process, known as dissolution, can create underground voids that occasionally collapse, causing sinkholes at the surface. The most well-known dissolution risk area in England is around Ripon in North Yorkshire, where gypsum dissolution has caused notable ground collapses. Chalk dissolution features are also found across the south-east, including parts of Hertfordshire and Kent.

A red flag for dissolution risk will prompt the buyer's solicitor to request specialist advice. Depending on the severity and the lender's requirements, this could involve a geotechnical assessment or ground-penetrating radar survey to check for voids beneath the property. These investigations can cost several hundred to a few thousand pounds.

Man-made cavities and mining

If the ground stability search identifies man-made cavities — such as former mine workings, tunnels, or old cellars — this overlaps with the territory covered by a coal mining search. In coal mining reporting areas, the buyer's solicitor will order a separate CON29M search from the Coal Authority. For non-coal mining areas (such as tin mining in Cornwall or lead mining in the Yorkshire Dales), a commercial mining search from a provider like Terrafirma or Groundsure may be recommended. The ground stability search flags the potential for man-made voids; the mining search investigates the specifics.

How ground stability results affect the conveyancing process

Ground stability is typically assessed as part of the standard environmental search, which returns within 24 to 48 hours. The search itself is rarely a source of delay. The delays come from what happens next — the follow-up enquiries, further reports, and lender requirements that can add days or weeks to your overall search timeline.

Here is how the process typically unfolds:

1. The buyer's solicitor orders the environmental search, which includes a ground stability section. Results return within 1 to 2 working days.
2. The solicitor reviews the ground stability results. Green results require no action. Amber or red results trigger enquiries.
3. Enquiries are raised with you (via your solicitor). Common questions include whether you are aware of any subsidence, whether any insurance claims have been made, and whether any structural repairs have been carried out.
4. You respond. If your TA6 form has been completed thoroughly — particularly Section 7.4 on subsidence, landslip, and ground heave — many of these enquiries will already be answered.
5. Further reports may be requested if the initial response does not resolve the concern. This might include a structural engineer's report, a geotechnical desk study, or a more detailed ground stability report from a specialist provider.
6. The mortgage lender reviews the position. If satisfied, the sale proceeds. If not, the buyer may need indemnity insurance, a price reduction, or a different lender.

The key point for sellers is that preparation matters. If you know your property sits on clay, is near a slope, or has had subsidence in the past, disclosing this early and having documentation ready will shorten the enquiry process significantly. For a broader view of how conveyancing costs break down, including search fees and follow-up report costs, see our conveyancing costs guide.

What sellers can do to prepare

You do not need to wait for the buyer's search to find out whether ground stability could be an issue for your property. Several free tools let you check the main geological risks yourself before you list:

• BGS Geology Viewer — The British Geological Survey's free online map at mapapps.bgs.ac.uk/geologyofbritain shows the bedrock and superficial geology beneath any location in Great Britain. If your property sits on London Clay, Oxford Clay, or another shrinkable formation, an amber flag for clay shrinkage is very likely.
• BGS GeoSure reports — The BGS offers paid GeoSure reports for individual properties, providing detailed hazard ratings for each ground stability risk category. These cost around 30 to 50 pounds and are available directly from the BGS website.
• Coal Authority interactive map — If you suspect former mining activity beneath your property, check the Coal Authority's free map at coalauthority.gov.uk to see whether you are in a mining reporting area.
• Insurance history — Check your buildings insurance records for any subsidence claims. If a claim was made and resolved, having the documentation ready will reassure the buyer's solicitor.
• Tree survey — If you have large trees close to the property and the soil is clay, consider whether they could be a concern. You do not need a formal arborist report at this stage, but being aware of the issue is helpful.

Sellers who want to go further can order the full set of property searches upfront — including the environmental search with its ground stability section. Having the results in hand before you accept an offer means you can answer enquiries immediately rather than waiting for the buyer's solicitor to order, receive, review, and then raise questions. This upfront approach can shave weeks off the post-offer conveyancing timeline.

Subsidence history and its effect on your sale

If your property has a history of subsidence — whether from clay shrinkage, mining, dissolution, or any other cause — you are legally required to disclose this on your TA6 form. Failure to disclose known subsidence can result in a misrepresentation claim after completion, which is far more costly and damaging than being transparent from the start.

A past subsidence claim does not make a property unsellable. The buyer's solicitor will want to see:

• Details of the original claim, including the cause of the subsidence and when it occurred
• Evidence that the issue was investigated and resolved — for example, an engineer's report confirming stabilisation, or underpinning certificates if underpinning was carried out
• Confirmation that buildings insurance is in place and does not exclude subsidence cover
• Monitoring data, if applicable, showing that ground movement has ceased

Properties with resolved subsidence claims are sold regularly. The main practical issue is that buildings insurance can be more expensive or harder to obtain if there is an unresolved claim or if the property has been underpinned. Having your insurance documents and any engineering reports ready to share will help the buyer's solicitor work through their due diligence efficiently.

When indemnity insurance can help

In some cases, rather than commissioning an expensive geotechnical investigation, the parties may agree to obtain indemnity insurance to cover a specific ground stability risk. This is a one-off premium — often under 100 pounds — that protects the buyer and their mortgage lender against future costs arising from the identified hazard.

Indemnity insurance is most commonly used where the ground stability search has flagged a theoretical risk (such as proximity to a dissolution zone) but there is no evidence of actual damage to the property. It is not a substitute for investigation where there are visible signs of ground movement, but it can be a pragmatic solution where the cost of a full geotechnical report would be disproportionate to the level of risk.

Your conveyancer will advise on whether indemnity insurance is appropriate in your circumstances. The buyer's mortgage lender will also need to accept the policy before the sale can proceed.

Sources and further reading

• British Geological Survey — GeoSure ground stability hazard data and methodology: bgs.ac.uk/products/geosure
• British Geological Survey — Geology of Britain viewer (free online geological mapping): mapapps.bgs.ac.uk/geologyofbritain
• British Geological Survey — Shrink-swell hazard information and research: bgs.ac.uk/geology-projects/shrink-swell
• Coal Authority — Interactive map of coal mining reporting areas: coalauthority.gov.uk
• GOV.UK — Land stability guidance for planning and development: gov.uk/guidance/land-stability
• Law Society — Conveyancing Protocol and guidance on property searches: lawsociety.org.uk
• Landmark Information Group — Residential environmental and ground stability search products: landmark.co.uk
• Groundsure — Ground stability and environmental search reports: groundsure.com
• Association of British Insurers — Guidance on subsidence claims and domestic property insurance: abi.org.uk

Frequently asked questions