What is land subsidence?

Subsidence is the downward movement of the ground beneath a structure, caused by the soil below shrinking, washing away or collapsing. Because it happens slowly and out of sight, it's often well advanced before anyone notices.

It helps to distinguish three related terms. Settlement is the gradual, usually harmless compression of ground under a new building's weight. Subsidence is sinking caused by the ground losing support — the one that damages structures. Heave is the opposite: the ground swelling and pushing upward. All three move buildings, but subsidence and heave are the ones that cause cracking and structural concern.

What causes subsidence in the UK

• Shrink-swell clay. Much of southern and eastern England sits on clay soils that swell when wet and shrink when dry. Long dry spells — increasingly common — cause the ground to contract and the structure above to drop.
• Trees and vegetation. Large trees draw moisture from clay soil, accelerating shrinkage near their roots, especially in dry summers.
• Leaking drains and water mains. Escaping water can wash fine material out of the ground, creating voids that the surface settles into.
• Historic mining and made ground. Old coal, chalk or mineral workings and poorly compacted fill can collapse or consolidate decades later.

Warning signs to look for

The classic indicators include new or widening cracks in walls — typically diagonal, wider at the top, and often near doors and windows — doors and windows that begin to stick, rippling wallpaper, and gaps opening where extensions meet the original building. On open land, look for depressions, sinkholes, tilting structures or fences, and cracking in hardstanding. A single hairline crack is rarely subsidence; it's progressive change over weeks and months that matters.

Why it matters

Beyond the structural risk, subsidence affects insurance and value. A history of subsidence can make cover harder to arrange and reduce what a property is worth, and remediation — which can run from monitoring to underpinning — is costly. Catching movement early, while it's still minor, gives you the widest and cheapest set of options.

How subsidence is detected

Traditionally, movement is tracked on the ground with level monitoring and crack gauges read over months. The newer, complementary approach uses satellite radar. Across Europe, the European Ground Motion Service publishes ground-motion measurements derived from Sentinel-1 radar (a technique called InSAR) that can detect vertical movement to millimetre precision, built up from repeated satellite passes. That means slow, large-area sinking or heave can be spotted from space — including on plots no one is physically monitoring.

What to do if you suspect subsidence

Don't panic at the first crack, but don't ignore progressive movement. Photograph and date cracks to track whether they're growing, check for obvious causes like a leaking drain or a nearby tree, and speak to a chartered structural engineer or your insurer if movement continues. Early, measured assessment beats reactive emergency works.

This guide is general information and is not structural, insurance or legal advice. If you suspect subsidence affecting a building, consult a chartered structural engineer and your insurer.