Finding a crack in a wall is one of the fastest ways to ruin a homeowner’s week. The good news: most cracks in walls are cosmetic, caused by plaster shrinkage, temperature changes or a house simply settling with age. The less good news: a small minority signal genuine structural movement — and telling the two apart from a photo on a forum is impossible. This guide explains what different cracks usually mean, which ones deserve professional attention, and what to do next.
Cracks That Are Usually Nothing to Worry About
Hairline cracks (under about 1mm) in plaster, cracks along plasterboard joints, and fine cracks around door frames after a hot summer or a new heating system are almost always benign. Newly built and newly plastered homes crack as materials dry out; older homes move gently with the seasons, especially on clay soils. Keep an eye on them, redecorate, and monitor.
Cracks That Deserve a Closer Look
Be more careful when a crack is wider than 3mm (roughly a pound coin’s thickness), diagonal and stepping through brickwork outside, wider at the top than the bottom, appearing around windows and doors that have started sticking, or growing month on month. Cracks that appear suddenly after nearby excavation, extension work or a long dry spell also justify attention — as does any crack you can see daylight through.
Does a Crack Mean Subsidence?
Usually not. Genuine subsidence — the ground beneath the foundations giving way — accounts for a small fraction of wall cracks, but it is the one that affects insurance, mortgages and saleability, which is why it needs ruling in or out properly. Clay shrinkage near mature trees, leaking drains washing away soil, and historic mine workings are the classic causes we see across Greater Manchester and the North West. Our subsidence surveys give you a clear written verdict on whether movement is historic, seasonal or active — and if it is active, a structural crack assessment or period of crack monitoring establishes exactly what is happening before anyone talks about underpinning.
What to Do Next
Photograph the crack next to a coin or ruler, note the date, and check it monthly. If it is growing, stepping through brickwork, or accompanied by sticking doors and sloping floors, get an RICS chartered surveyor to inspect it. It is a fixed-fee visit that either buys you peace of mind or catches a genuine problem early — both outcomes are worth considerably more than the fee. Get a fixed-fee quote or call 020 4579 8270 and we will tell you honestly whether it needs an expert at all.