What Is Subsidence and How Does It Affect a House Survey?

Subsidence is one of the more serious issues a property survey can flag. If a surveyor identifies signs of it — or refers to it in your report — understanding what it means and what happens next is essential before you make any decisions.

What Is Subsidence?

Subsidence is the downward movement of the ground beneath a building. Unlike settlement — which is a normal, gradual process that occurs in new buildings over time — subsidence tends to be uneven and is often caused by changes in the soil beneath or around the foundations.

When the ground sinks unevenly, different parts of the building are affected differently. This differential movement is what causes cracking, distortion of openings, and, in more serious cases, structural instability.

It is important to distinguish subsidence from normal ageing. Many older properties show minor cracks or slight movement that has been stable for many years and poses no ongoing risk. A surveyor’s role is to assess whether movement appears to be historic and stable, or whether it may be active and progressive.

What Causes Subsidence?

Subsidence may occur for a number of reasons, depending on the ground conditions and the property’s environment:

• Clay shrinkage: Clay soils shrink in dry weather and expand when wet. Properties on clay-heavy ground are at higher risk of movement, particularly in dry summers.
• Tree root activity: Large trees near a building can extract moisture from clay soils, causing them to shrink. This is one of the most common causes of subsidence in English residential properties.
• Leaking drains: Underground drainage that is cracked or leaking can wash away the soil beneath foundations over time, creating voids that cause movement.
• Mining legacy: In areas with historic coal or mineral extraction, old workings can settle over time and affect the ground above.
• Poor original foundations: Older properties may have shallow or inadequate foundations that are more susceptible to movement.

What Signs Does a Surveyor Look For?

A surveyor cannot diagnose subsidence from a single inspection alone — the history of movement matters as much as the current state. However, certain signs may prompt them to flag the possibility:

• Diagonal cracking at the corners of windows and door frames, often described as “stair-step” cracking in brick joints
• Cracks that are wider at the top than the bottom, suggesting downward movement
• Doors and windows that stick, particularly on one side of the property
• Visible displacement between sections of a wall
• Sloping or uneven floors, particularly in older buildings
• Cracking in external render that follows the brick coursing pattern

Many of these signs can have causes other than subsidence — thermal movement, poor original construction, or simple ageing. The surveyor will consider the size, pattern, and distribution of any cracking alongside the age and construction of the property.

How Is Subsidence Assessed in a Survey?

During a RICS Level 3 Building Survey, the surveyor will document any visible signs of movement, note whether they appear historic or potentially active, and assess the likely cause where possible. A Level 2 Home Survey will also flag potential movement concerns, though typically with less detailed analysis.

Where signs of possible subsidence are found, the surveyor may give the relevant elements a Condition 3 rating, recommend a structural engineer’s report, suggest that the buyer requests records from the vendor about any previous movement or insurance claims, and recommend that the buyer’s solicitor makes enquiries about drainage and planning history.

It is not usually possible to confirm active subsidence from a single survey inspection. Movement monitoring — placing tell-tales or taking measurements over time — is often required to determine whether movement is ongoing.

Subsidence and Property Insurance

Properties with a history of subsidence can be more difficult and expensive to insure. If a property has had subsidence-related insurance claims in the past, the vendor should disclose this, and the buyer’s solicitor should check whether the repairs were carried out under insurance and whether any guarantees are in place.

Your surveyor can help you understand the implications of any disclosed subsidence history and whether the remedial works appear to have been appropriate. For specialist structural concerns, a specific defect report may provide additional detail.

What Happens if Subsidence Is Confirmed?

Underpinning

This involves strengthening or deepening the foundations beneath the affected part of the building. It may be carried out using traditional mass concrete, mini-piling, or other methods depending on the cause and ground conditions. A property that has been properly underpinned, with the cause resolved and documented, may be structurally sound.

Root Barrier or Tree Removal

If tree root activity is identified as the cause, removing the tree or installing a root barrier may stabilise the situation without the need for underpinning.

Drainage Repair

Where leaking drains are the cause, repairing the drainage and allowing the ground to restabilise may be sufficient, depending on whether any long-term foundation damage has occurred.

Should Subsidence Concerns Stop a Purchase?

Not automatically. The key questions are: Is the movement current and active, or historic and stable? Have previous repairs been carried out, and do they come with documentation or guarantees? Does the property’s insurance situation reflect the history accurately? Has the cause been identified and addressed, or does it remain unresolved?

A well-documented history of past subsidence, properly repaired and insured, may be far less of a concern than newly discovered movement with no known cause. Your surveyor and solicitor can help you put the risk in context. You can also find guidance on related structural issues at our general information hub.

If you are buying in Lincolnshire specifically, our local guide to subsidence risk in Lincolnshire explains the county’s specific geological conditions — including boulder clay and Fen peat soils — and what buyers should look for in their survey.