Subsidence is one of the most feared words in property. The mention of it can derail a sale, cause mortgage offers to be withdrawn, and make insurance difficult to obtain. But understanding what subsidence actually means — and when it is and isn’t serious — can help you navigate a purchase with confidence.
What Is Subsidence?
Subsidence occurs when the ground beneath a building’s foundations shifts or sinks, causing the building to move and crack. It is different from settlement (which is normal movement of a new building as it beds in) and heave (upward movement of the ground, which typically affects properties on clay soils during wet periods).
What Causes Subsidence?
The most common causes in the UK are shrinkable clay soils (which expand when wet and shrink when dry — particularly near trees that extract moisture), drain leaks (which wash away soil beneath foundations), and inadequate original foundations. Clay subsidence is most prevalent in London, the South East, Midlands and parts of East Anglia.
What Are the Warning Signs?
Not all cracks indicate subsidence. Hairline cracks and those under 2mm wide are common in all buildings and usually reflect normal thermal or moisture movement. Cracks associated with subsidence tend to be: diagonal, wider at the top than the bottom; wider than 5mm; extending through brickwork rather than just the render; and accompanied by sticking doors or windows as the frame distorts.
How Is Subsidence Detected in a Survey?
A RICS Level 3 Building Survey will identify cracking patterns and assess whether they are consistent with subsidence. If the surveyor believes subsidence is possible, they will recommend further specialist investigation — typically a structural engineer’s report and possibly trial pits to examine the foundations.
Should I Still Buy a Property With Subsidence?
A history of subsidence does not necessarily mean you should walk away. The key questions are: has the cause been identified and resolved? Has the movement stabilised? Is it insurable? Many properties with historic subsidence — where tree roots have been removed and foundations underpinned — are perfectly stable and insurable. A specialist report and an honest conversation with your surveyor will give you the information you need.
Get a Proper Survey
If you’re buying a property in an area known for clay soils — London, South East, Midlands — a Level 3 Building Survey is strongly advisable. Find Building Surveyors near you →