Subsidence, Causes, Signs, Insurance Implications and What Buyers Should Do

What is Subsidence?

Subsidence occurs when the ground beneath a building moves downward unevenly, causing the foundations, and therefore the structure above, to move, crack, and potentially become unsafe. It is distinct from **settlement**, which refers to normal compaction of ground under a new building's weight and typically stabilises within a few years of construction.

Subsidence is treated differently by insurers, mortgage lenders, and surveyors because it indicates an active or historic instability in the ground, a condition that may recur and that requires investigation before a property can be confidently bought or sold.

Common Causes

• **Tree root extraction**, The most common cause in the UK. Clay soils, which cover large areas of south-east England, shrink when moisture is removed by roots. In dry summers, clay shrinkage can be dramatic. The Association of British Insurers (ABI) identifies trees within 7 metres of a property as a material risk factor.
• **Clay soil shrink-swell**, Even without trees, expansive clay soils can move seasonally, particularly in prolonged dry or wet periods
• **Leaking drains**, Water from a fractured drain can wash fine soil particles away (known as soil washing or piping), creating voids beneath foundations
• **Mining legacy**, Properties in former coal-mining areas of England and Wales may be affected by old mine workings collapsing beneath them; these areas are covered by the Coal Authority's interactive map
• **Poorly compacted made ground**, Sites previously used for landfill or infill can compress unpredictably over decades

How to Spot Subsidence

Not all cracks are subsidence. The key indicators that elevate concern include:

RICS guidance classifies cracks using the Building Research Establishment's (BRE) 6-category scale from Category 0 (hairline, cosmetic) to Category 5 (structural instability requiring immediate action).

Insurance Implications

A property with a history of subsidence, even if it has been successfully stabilised and underpinned, will be classed as a non-standard risk by most mainstream insurers. Consequences include:

• Higher buildings insurance premiums
• Larger excesses for subsidence-related claims (typically £1,000–£2,500)
• Some insurers declining to quote at all
• Difficulty obtaining cover if the cause has not been identified and rectified

If a property has had a subsidence insurance claim, the seller is legally obliged to disclose this on the Property Information Form (TA6). Failure to disclose is grounds for a legal claim after purchase.

What Buyers Should Do

1. **Commission a Level 3 Building Survey** (formerly full structural survey), the only survey type that adequately investigates subsidence risk. RICS-regulated surveyors will assess crack patterns, drainage, vegetation, and soil type.

2. **Request all insurance history**, ask the seller specifically whether any subsidence claim has been made, and obtain documentation of any remedial works

3. **Check drainage condition**, a CCTV drain survey is advisable where drain defects are a plausible cause

4. **Consult the Coal Authority**, if the property is in a former mining area, the Coal Authority's search (obtainable via your solicitor) will identify any known mine workings

Property Passport UK displays geological data and flood zone information that can help buyers identify clay soil areas and other environmental risk factors before commissioning surveys.

Underpinning

Underpinning involves strengthening the foundation, typically by extending it to a greater depth or using resin injection or mini-piles. A successfully underpinned property with a clear engineer's completion certificate and insurance cover in place is generally considered stable. However, the stigma attached to the word "underpinned" means it can still affect resale value and insurance premiums for many years.