What Is Subsidence?
Subsidence is the downward movement of the ground beneath a building's foundations, causing the structure to sink unevenly. This creates stress in walls, floors, and the building fabric, typically manifesting as cracking.
It is distinct from settlement (which occurs naturally in new buildings) and heave (upward ground movement, often caused by clay soil expanding after tree removal).
Signs of Subsidence
Look for these warning signs when viewing a property:
- Diagonal cracking — cracks that run diagonally from window or door corners, wider at the top than the bottom
- Cracks wider than 3mm — hairline cracks are usually cosmetic; wider cracks need investigation
- Doors and windows sticking — frames distort as the structure moves
- Cracks that reappear after being filled — indicates ongoing movement
- Rippling wallpaper — can indicate wall movement beneath
- Previous underpinning — check with the seller and solicitor
What Causes Subsidence?
- Clay soil shrinkage — the most common cause in the UK, especially in London, Essex, and Kent
- Tree root action — trees extracting moisture from clay soils near foundations
- Leaking drains — washing away or softening ground beneath foundations
- Mining activity — historic mining can create voids
- Inadequate foundations — older properties with shallow foundations are more vulnerable
When Do You Need a Subsidence Survey?
If you see signs of subsidence when viewing a property or your surveyor identifies concerns, a structural survey will investigate the cause, severity, and required remediation.
We recommend at minimum a Level 3 Building Survey for any property showing signs of movement. This includes crack mapping, assessment of foundation type, analysis of nearby trees and drainage, and remediation recommendations.
Subsidence and Insurance
A history of subsidence can make it harder to obtain buildings insurance, and premiums may be higher. However, if remediation has been successfully completed and monitored, most insurers will cover the property. Always check the subsidence history before committing to a purchase.
Subsidence Repair Costs
Repair costs depend on severity:
- Tree management: £500–£5,000 (if trees are the cause)
- Drain repair: £1,000–£5,000
- Underpinning: £10,000–£50,000+ depending on extent
Understanding these costs before purchase is essential for informed negotiation.