Roof, walls & outside
Cracks in walls: which ones matter
Every house in Britain has cracks, and nearly all of them are plaster doing seasonal stretches. A small number are the building reporting genuine movement. The skill is telling the two apart calmly, with a pencil and a camera rather than a panic.
By the Tickover team · Published 20 February 2026 · 4 min read
How urgent is this?
Most cracks: monitor, not mourn
Hairlines can wait for the next redecoration. Stepped brickwork cracks, anything wider than 5mm, or doors suddenly sticking jump the queue to a surveyor.
Reading a crack like a surveyor
Plaster and mortar shrink, swell and settle with the seasons; that is where hairlines come from, especially around new plaster, plasterboard joints and freshly heated winter rooms. Structural movement writes differently: it follows the weak lines of the building, opens wider than it should, and brings friends, like doors that stopped fitting their frames last month.
| What you see | Usual story | Move |
|---|---|---|
| Hairline in plaster | Drying or seasonal movement | Fill and repaint when redecorating |
| Straight line between boards | Plasterboard joint flexing | Tape, fill, repaint |
| Diagonal from door or window corner | Settlement or lintel movement | Monitor; surveyor if it grows |
| Stepped along brick mortar joints | Possible foundation movement | Surveyor |
| Wider than 5mm or visible both sides | Structural until proven otherwise | Surveyor now |
The four tells that end the wait-and-see phase: a crack that steps down the mortar joints of brickwork, a width beyond 5mm (wider than a £1 coin is thick, with room to spare), doors or windows that suddenly stick or swing, and any crack you can find on both faces of the same wall. One of those is a surveyor conversation, not a filler purchase.
The monitoring routine
Monitor a crack properly
Mark both ends in pencil, with the date
A dated tick just beyond each tip. If the crack outgrows its marks, it is live, and you know exactly when it moved.
Measure the widest point
A coin makes a repeatable gauge: note where a £1 coin edge slots in and how far. Callipers if you own them, but consistency beats precision.
Photograph with a ruler in shot
Same angle, same daylight, coin or ruler for scale. Store them somewhere dated; your house paperwork file is the natural home.
Re-check monthly, and after dry summers
Clay soils shrink hardest in drought, so late summer is when movement cracks perform. A calendar reminder does the remembering.
Escalate on growth
Wider, longer, new companions, or doors joining in: stop monitoring and get a professional opinion.
That overlap with damp cuts both ways. A cracked external wall can feed penetrating damp, and a long-running leak or blocked gutter can soften ground near foundations. If your crack comes with a damp patch, work through which kind of damp you have as part of the same investigation, and give the outside walls the twice-yearly scan from the outside survival guide.
Subsidence, said calmly
Subsidence means the ground under part of the building is giving way, classically clay soil shrinking in dry summers, often with thirsty trees involved, or a leaking drain washing fines away. It is serious, insurable and slow. If a surveyor suspects it, your insurer appoints engineers, monitors the movement for a period, fixes the cause (tree management or drain repair far more often than underpinning), and repairs the cosmetics at the end. The excess is typically higher than for other claims, and the process is measured in months. None of that is improved by panicking early, and all of it is improved by your dated photos.
Want a professional read on that crack?
Describe it to Tickover Advice with your photos: a free property-aware draft now, and from £49 a chartered MRICS surveyor verifies and signs the answer.
Quick answers
When should I worry about a crack in a wall?
When it steps along the mortar joints of brickwork, measures wider than 5mm, appears on both sides of the same wall, or arrives alongside doors and windows that suddenly stick. Any one of those deserves a surveyor. Fine cracks in plaster with none of those features are usually seasonal movement and can wait for redecorating.
Is a cracked wall always subsidence?
No, and most are not. New plaster shrinks, plasterboard joints flex, lintels rust and settle, and heating cycles open hairlines every winter. Subsidence is one specific cause with its own signature: stepped or widening cracks, often worse in late summer on clay soils, sometimes with sticking doors. Monitoring for a few months usually separates the two.
Should I claim on insurance for cracks?
Only once a professional suspects genuine structural movement, because subsidence claims carry a higher excess, take months of monitoring, and sit on the property’s record permanently. For a crack with no other symptoms, pay for an independent opinion first. If the surveyor does suspect subsidence, involve your insurer promptly; delay is the thing they hold against you.
Can I fill a crack and repaint?
Yes, once you know what it is. For hairlines and stable joint cracks, flexible filler and a repaint is the complete fix. The mistake is filling a crack you have not monitored: you erase the evidence and start the clock again. Mark it, photograph it, watch it for a season, then decorate over the boring ones with a clear conscience.
This guide is general information for UK homes, not advice about your specific property. Anything involving gas must be done by a Gas Safe registered engineer, and notifiable electrical work by a qualified electrician. If you smell gas, call the National Gas Emergency line on 0800 111 999. If you’re ever unsure, stop and get a professional in — that’s exactly what Tickover is for.
Keep reading
Roof, walls & outsideFull guide
Roofs, gutters and walls: the outside survival guide
How rain should travel from ridge to drain, the ground-level checks that catch roof, gutter and wall trouble early, and how to hire a roofer well.
7 min read
Damp, mould & air
Condensation or rising damp? Tell them apart
Tide marks or corner mould? The foil test, the signs that separate condensation from rising damp, and why free damp surveys deserve a second opinion.
4 min read
Damp, mould & air
Penetrating damp: find the way in
A damp patch that grows after rain has a way in somewhere. How to trace it from gutters to pointing, and why the inside fix always waits.
3 min read