Almost every home in London has cracks somewhere. Most are harmless – plaster shrinkage, seasonal movement, a house simply being a house. A few are the first visible sign of subsidence or structural movement that gets more expensive the longer it is ignored. The difficulty for a homeowner is telling one from the other, so here is the honest guide our surveyors give friends and family.
Cracks that are usually nothing to worry about
Hairline cracks in plaster (under about 1mm), crazing on new plaster, straight cracks along plasterboard joints, and fine cracks above doors and windows that have been stable for years are overwhelmingly cosmetic. They come from shrinkage, temperature cycles and the normal settling of materials. Fill them, repaint, and keep an occasional eye on them.
Cracks that deserve a closer look
Take more notice when a crack is wider than about 3mm (a £1 coin’s thickness), when it is diagonal and stepped through brickwork rather than plaster, when it appears suddenly or keeps reopening after filling, when it sits close to a bay window, porch or extension junction, or when doors and windows nearby have started sticking. Cracks that are wider at the top than the bottom, or that mirror each other inside and out, suggest the movement goes through the structure rather than just the finish.
The subsidence question
London’s clay soil shrinks in dry summers and swells in wet winters, and mature trees close to shallow Victorian foundations make it worse. Classic signs of subsidence are stepped diagonal cracking concentrated around one corner or bay, sloping floors, and gaps opening between walls, skirtings and frames. Insurers deal with subsidence every year and a well-evidenced early diagnosis usually means monitoring or targeted repair – not the horror stories.
What to do next
Photograph the crack with a coin for scale, note the date, and check again after a few weeks. If it is growing, stepped, or accompanied by sticking doors, get it assessed professionally. Kingston Surveyors arranges independent structural crack assessments and subsidence surveys across London and the UK – a chartered specialist classifies the damage, identifies the cause and tells you plainly whether it matters. Call 0204 579 8270 for a free, no-obligation quote.
