What is subsidence, and what should you actually do about it?
The downward movement of the ground beneath a building's foundations, causing the structure to move with it. It is the most feared word in home ownership, and the fear is disproportionate to how most cases actually resolve.
The distinction that matters. Subsidence is the ground sinking. Heave is the ground swelling upward — usually after a large tree is removed from clay soil, which then rehydrates. Settlement is the normal, expected compression of ground under a new building, and is not a defect. Confusing these leads to entirely the wrong remedy.
The usual causes:
Clay shrinkage, which is by far the most common. Clay soils shrink in dry weather and swell when wet, and tree roots extracting moisture accelerate it enormously. This is why claims spike after dry summers.
Leaking drains, washing away fine material beneath foundations. Frequently the cause and frequently overlooked.
Poorly compacted made ground, or historic mining.
Nearby excavation.
The signs, and what distinguishes them from ordinary cracking:
Diagonal cracks wider at the top than the bottom.
Cracks wider than about 3 mm, visible both inside and outside, and typically near doors and windows.
Doors and windows sticking where they did not.
Rippling wallpaper at wall and ceiling joins.
Most cracks are not subsidence. Seasonal movement, plaster shrinkage in new work, and thermal expansion produce fine cracks routinely.
What to do, in order:
Do not panic and do not call an underpinning company first.
Contact your insurer. Subsidence is a standard peril on buildings insurance, and the insurer appoints a loss adjuster and engineer. Making a claim is the correct step even knowing it affects future insurability.
Monitoring comes first, typically over a year, to establish whether movement is progressive or seasonal.
Fix the cause — drain repair, tree management. Most cases are resolved this way, and underpinning is comparatively rare and used when nothing else will do.
Disclosure is required at sale, and insurance follows the property.
General information, not legal advice.