Subsidence Explained: Causes, Signs, and Solutions

📅 October 2024 📖 10 min read ✍️ Expert Surveyors UK
Subsidence cracks in brick wall showing diagonal pattern

Expert Surveyors UK assesses hundreds of subsidence cases annually. Subsidence is one of property buyers' biggest fears, yet many cracks wrongly get diagnosed as subsidence when they result from other causes. Understanding subsidence helps you identify genuine problems and avoid panic over minor settlement cracks.

In this guide, our RICS chartered surveyors explain what subsidence is, how to identify it, what causes it, and the remedial works required to fix it. We also cover related issues like heave and settlement, helping you distinguish between different types of structural movement.

What is Subsidence?

Subsidence occurs when the ground beneath a building moves downward, causing foundations to sink and resulting in structural damage. This differs from settlement (normal gradual compression of soil under building weight) and heave (ground swelling and pushing foundations upward).

True subsidence is relatively rare and usually affects properties in specific circumstances. Many cracks wrongly attributed to subsidence actually result from thermal movement, settlement, or other benign causes.

Expert Surveyors UK's building pathology expertise helps distinguish genuine subsidence from other forms of structural movement, preventing unnecessary alarm and expensive remedial works.

Common Causes of Subsidence

1. Clay Soil Shrinkage

The most common subsidence cause in the UK. Clay soils shrink during dry weather, particularly extended dry periods, causing foundations to lose support. Properties in the South East, where clay soils predominate, are particularly vulnerable.

Factors affecting clay shrinkage include:

2. Tree Root Activity

Trees near properties can cause subsidence by extracting moisture from clay soil. High water-demand species pose particular risks:

Our building surveyors assess tree locations, species, and sizes when investigating potential subsidence, determining whether trees contribute to foundation movement.

3. Leaking Drains

Defective drains can wash away soil beneath foundations, particularly in sandy or gravelly soils. Long-term leaks create voids under buildings, leading to sudden settlement or gradual subsidence.

4. Mining and Ground Works

Past coal mining, chalk extraction, or other excavations can cause ground instability decades later as old mine workings collapse. Properties in former mining areas remain at risk, though mining records help identify vulnerable locations.

5. Made Ground

Buildings constructed on filled or made-up ground (old rubbish tips, filled quarries, or building rubble) risk subsidence as fill material consolidates over time.

Signs of Subsidence

Subsidence shows distinctive patterns that Expert Surveyors UK's chartered surveyors recognize during building surveys:

Crack Characteristics

Other Subsidence Indicators

Not all these signs indicate subsidence. Our building surveyors investigate thoroughly, determining whether movement is historic, ongoing, or caused by other factors like thermal movement or settlement.

Subsidence vs Settlement vs Heave

Settlement

Normal compression of soil under building weight, typically occurring in the first 10-15 years after construction. Settlement cracks are usually hairline width, stable, and don't progress. Most older properties show historic settlement cracks that don't require remedial works.

Subsidence

Downward foundation movement from external factors like clay shrinkage or tree roots. Subsidence cracks are typically wider, progressive, and require investigation and potential remedial works.

Heave

Upward ground movement from clay expansion, often occurring after tree removal allows clay to rehydrate. Heave causes different crack patterns from subsidence, typically showing wider cracks at the bottom than top.

Expert Surveyors UK's building pathology expertise distinguishes between these movement types, ensuring correct diagnosis and appropriate remedial works recommendations.

Investigating Subsidence

When subsidence is suspected, thorough investigation is essential:

Building Survey

Our RICS chartered surveyors conduct comprehensive inspections, examining:

Crack Monitoring

Many building surveyors recommend monitoring cracks over 6-12 months to establish whether movement is ongoing. Crack monitors (tell-tales) indicate movement direction and extent.

Specialist Investigations

For serious cases, specialist investigations may include:

Remedial Works for Subsidence

Subsidence remedial works vary depending on cause and severity:

Tree Management

If trees cause subsidence, options include:

Tree removal isn't always the best solution. Our chartered surveyors advise on appropriate tree management balancing subsidence risk with heave prevention.

Underpinning

The most common subsidence remedy, underpinning extends foundations to deeper, more stable ground. Traditional mass concrete underpinning costs £10,000-£50,000+ depending on extent and property size.

Underpinning types include:

Drain Repairs

If leaking drains cause subsidence, repairing or replacing defective drainage often solves the problem at much lower cost than underpinning.

Crack Repair

Once movement stabilizes, repairing cracks restores appearance and weather-tightness. Methods include:

Cosmetic repairs should wait until movement stops, otherwise cracks will re-open.

Insurance and Subsidence

Most home insurance policies cover subsidence (check your policy for excess amounts, typically £1,000). However, insurers may:

Expert Surveyors UK provides expert witness services when insurance disputes arise, offering impartial opinions on whether subsidence occurred, likely causes, and appropriate remedial works.

Buying Properties with Subsidence History

Properties with past subsidence don't necessarily pose risks if:

Our building surveyors assess previous subsidence repairs, advising whether remedial works were appropriate and whether further issues are likely. Properties with treated subsidence often represent good value if properly repaired.

Preventing Subsidence

While you can't eliminate subsidence risk completely, preventive measures help:

Regional Variations in Subsidence Risk

Subsidence risk varies across the UK:

Expert Surveyors UK operates throughout the UK, understanding regional geology and subsidence patterns that affect properties throughout different areas.

When to Seek Professional Advice

Contact our RICS chartered surveyors if you notice:

Conclusion

Subsidence causes concern for property owners, but accurate diagnosis prevents unnecessary panic and expense. Many cracks result from normal settlement or thermal movement rather than genuine subsidence requiring expensive remedial works.

Expert Surveyors UK's RICS chartered surveyors bring years' experience and building pathology expertise to subsidence investigations. Our building surveys identify whether movement is ongoing, determine causes, and recommend appropriate remedial works that address root problems rather than just treating symptoms.

Whether you're buying a property with visible cracking, experiencing new cracks in your home, or need expert witness evidence for subsidence disputes, our professional assessments provide the clarity and confidence you need.

Concerned About Subsidence?

Expert Surveyors UK provides comprehensive subsidence investigations. Our RICS chartered surveyors identify causes and recommend cost-effective solutions.

Book a Subsidence Survey

Related Articles