What causes subsidence
Subsidence happens when the soil supporting a building's foundations moves downward, usually because it loses moisture and shrinks. Properties on shrinkable clay soils are most at risk, particularly during hot, dry summers.
Nearby trees and large shrubs are a frequent culprit, as their roots draw water from the soil. Leaking drains that wash away ground material, and historic mining or made-up ground, can also cause it. Knowing the cause is essential, because the fix depends on it.
Warning signs to look for
- New, diagonal cracks wider than around 3mm, often near windows and doors.
- Cracks that are wider at the top than the bottom.
- Doors and windows sticking for no obvious reason.
- Rippling or tearing wallpaper at wall-ceiling joints.
- Visible leaning or sinking of an extension, bay or porch.
- Cracks visible both inside and outside in the same place.
Subsidence vs settlement vs heave
| Type | What it is | Concern level |
|---|---|---|
| Settlement | New build bedding down into the ground | Usually minor |
| Subsidence | Ground sinks, foundations drop | Serious, needs investigation |
| Heave | Ground swells and pushes foundations up | Serious, needs investigation |
A surveyor or structural engineer can tell which you're dealing with.
What to do if you suspect subsidence
Get a detailed survey
Commission a RICS Level 2 (HomeBuyer) or, ideally, Level 3 (Building) survey to assess the cracks.
Commission a structural report
If flagged, a structural engineer identifies the cause and whether movement is ongoing.
Check the history
Ask the seller about past subsidence, repairs, underpinning and any insurance claims.
Confirm insurability
Check you can get buildings insurance and whether the existing insurer will transfer cover.
Renegotiate or walk away
Use the findings to negotiate a discount, require repairs, or withdraw if the risk is too high.
Treated subsidence isn't always a dealbreaker
A property with historic subsidence that's been properly repaired, documented and insured, ideally with a structural engineer's certificate and a transferable insurance history, can be a sound buy, often at a negotiated discount.
Insurance can be the bigger hurdle
A history of subsidence can push up premiums and excesses, and some insurers won't quote at all. The simplest route is often to take over the existing insurer's policy. Confirm cover is available, and affordable, before you exchange.