Most cracks in brickwork are thermal movement or old settlement and need nothing but repointing. The ones that matter are wider at one end, run diagonally through bricks rather than along joints, continue inside, and are getting worse. Width, direction and whether it is moving decide it — not how alarming it looks.
- A crack that follows the mortar joints is usually far less serious than one through the bricks.
- Diagonal and tapering means movement. Vertical and even-width usually means thermal.
- Under 5mm and stable is almost always cosmetic. Over 15mm needs an engineer.
- Monitor before you excavate. Most suspected subsidence turns out to be stable.
Read the crack before you worry about it
Cracks in brickwork alarm people out of proportion to what most of them mean. Nearly every house has some, and the great majority are doing nothing.
Four things tell you whether a crack matters, and you can assess all four yourself.
Width. Hairline to 5mm and stable is cosmetic. Five to 15mm is worth watching and getting looked at. Over 15mm, or wide enough to put a finger in, needs a structural engineer rather than a builder.
Direction. Diagonal cracks that step up through the brickwork indicate differential movement — one part of the building moving relative to another. Vertical cracks of even width are usually thermal expansion. Horizontal cracks at regular intervals are usually wall tie failure, which is a different problem again.
Taper. A crack that is wider at the top than the bottom, or vice versa, is a movement crack: something is rotating or sinking. A crack of even width along its length is far less concerning.
Whether it continues inside. A crack visible on the outside and in the same place internally has gone through the full thickness of the wall. That is more significant than one confined to the outer face.
The single most useful question is not how big it is but whether it is getting bigger. A 10mm crack that has been exactly 10mm for twenty years is an historical event. A 3mm crack that was not there last autumn is worth attention.
What each pattern usually means
| What you see | Usual cause | What to do |
|---|---|---|
| Fine vertical cracks, even width | Thermal movement | Repoint; add a movement joint if recurring |
| Stepped diagonal, wider at top | Subsidence below that corner | Engineer; monitor before excavating |
| Stepped diagonal, wider at bottom | Heave, or rotation | Engineer |
| Horizontal cracks every sixth course | Corroding wall ties | Tie replacement; not foundations |
| Crack above a window or door | Failed or undersized lintel | Lintel replacement |
| Crack at a junction of old and new | Differential settlement | Often stable; monitor |
| Outer leaf bulging outwards | Tie failure, or retained earth | Engineer; stop before it progresses |
| Crack through bricks, not joints | Significant force | Engineer |
| Vertical crack at a corner, full height | Rotation of a return wall | Engineer |
| Stepped crack near a tree | Clay shrinkage from root uptake | Engineer; tree management |
Rows four and five account for a large share of what gets reported as subsidence, and neither has anything to do with foundations. Wall tie failure and a failed lintel are both routine, contained repairs.
Subsidence, settlement and heave are not the same
Settlement
The building bedding into the ground under its own weight, usually in the first few years after construction or after an extension is added. It is normal, it stops, and the cracks it leaves are historical. Most of the old cracks in an older house are this. Nothing needs doing beyond making good.
Subsidence
The ground beneath the foundation moving downwards for a reason unrelated to the building's weight — most often clay soil shrinking in dry weather, frequently accelerated by tree roots drawing moisture out, and sometimes a leaking drain washing fines out of the subsoil. This is progressive and it is the one that needs addressing. It is also far less common than the number of people who think they have it.
Heave
The opposite: ground swelling upwards, typically clay rehydrating after a large tree has been removed. It can take years to play out and it can do more damage than subsidence because the forces are greater. This is why felling a mature tree close to a house on clay is not automatically the right move.
Thermal movement
Materials expanding and contracting with temperature. Long runs of brickwork with no movement joint crack somewhere, and it will be at the weakest point. The crack opens in winter and closes in summer, which is a useful diagnostic: a crack that changes with the season is thermal, not structural.
Monitor before you dig
The instinct on finding a worrying crack is to act. The correct first step is almost always to measure it and wait, because the remedy depends entirely on whether it is moving.
How to monitor properly:
- Photograph it with a ruler or coin in shot, and write the date on the photograph.
- Measure the width at a marked point — pencil a small line across the crack so you measure the same spot each time.
- Use a crack gauge if you want proper numbers. They cost very little, fix across the crack, and give a direct reading in two axes.
- Record monthly for a year. A full year matters, because thermal and clay movement are both seasonal and six months of data can point the wrong way.
- Note the weather. A long dry summer is when clay shrinkage shows.
- Check the drains in the meantime, because a leaking drain is a common and fixable cause.
A year of readings showing no change converts an anxious unknown into a cosmetic repair. A year showing steady progression gives an engineer or an insurer something to act on. Either outcome is worth far more than an excavation started on a guess, and underpinning is both expensive and something that has to be declared when you sell.
Lintels and bulges: two specific repairs
Two structural problems come up often enough to describe on their own, and neither is subsidence.
Failed lintels. A crack above a window or door, often stepping diagonally from the corner of the opening, usually means the lintel is failing. On older houses the lintel may be a timber bressummer that has decayed, a shallow brick arch that has dropped, or a steel lintel that has corroded and expanded — rusting steel in brickwork lifts the courses above it just as a wall tie does. The repair is to prop, cut out and replace with a correctly sized lintel bearing properly at each end. It is a contained job.
Bulging walls. An outer leaf bowing outwards has lost its restraint. On a cavity wall that means the ties; on a solid wall it means the bond between leaves or the connection to the floors has failed. It can also be a retaining situation — earth or a raised patio pushing against a wall never designed to hold it. Bulging is more serious than cracking because it is a stability question rather than a cosmetic one, and it needs an engineer. The usual remedies are tie replacement, helical restraint bars, or lateral restraint straps tying the wall back to the floor joists.
Neither needs foundation work, and both get misdiagnosed as subsidence because the crack pattern can look similar from the ground.
When to call an engineer rather than a builder
- Any crack over about 15mm, or wide enough to see daylight through.
- A crack that is measurably growing over months.
- Cracks through the bricks rather than the mortar joints.
- Doors and windows binding where they used to close, which indicates the opening has gone out of square.
- Any bulge in a wall.
- Floors noticeably sloping or a new gap at the skirting.
- Cracking after a nearby excavation, a new extension next door, or a tree being removed.
- Before buying, where a survey has flagged movement and you need to know the cost.
A structural engineer gives you a written assessment and, where work is needed, a specification a builder can price against. That order matters: a builder pricing a structural repair without a design is guessing, and the paperwork is what a buyer's solicitor and your insurer will later want to see. Where subsidence is suspected and you are insured, speak to the insurer before commissioning anything, because they will usually appoint their own.
What it costs
These are the building figures published across this site:
| Job | Typical Coventry guide price | Notes |
|---|---|---|
| Builder, hourly | £20–£40/hr (avg ~£24) | Skilled trade |
| Builder, day rate | £200–£350/day | Varies with firm size |
| Repointing | £20–£50 per m² | Brick condition dependent |
| Remove load-bearing wall + steel | £1,500–£3,000 | Includes calcs & building control |
A structural engineer's inspection and report is a separate cost and is not in the table above. It is money well spent before any structural repair, because it establishes both what is actually wrong and what a builder should be pricing.
We will tell you whether it reads as thermal, historical or active — and say plainly when it needs an engineer rather than us.
Frequently asked questions
When is a crack in brickwork serious?
When it is over about 15mm, tapering rather than even in width, running diagonally through the bricks rather than along the mortar joints, visible inside as well as out, and measurably growing. Width alone is less telling than whether it is moving, so measure it before deciding.
How do I know if I have subsidence?
Stepped diagonal cracking that is wider at the top, doors and windows binding, and progression over months. But most suspected subsidence turns out to be old settlement, thermal movement, wall tie failure or a failed lintel. Monitor for a full year before excavating anything.
What is the difference between settlement and subsidence?
Settlement is the building bedding into the ground under its own weight, usually soon after construction or an extension. It stops, and its cracks are historical. Subsidence is the ground itself moving down for another reason — clay shrinkage, tree roots, a leaking drain — and it is progressive.
What causes horizontal cracks in brickwork?
Almost always corroding wall ties, particularly in houses from the 1920s to 1960s. The steel rusts, rust takes more volume than the steel did, and it lifts the mortar bed. The giveaway is cracking at regular intervals of roughly six courses. It is nothing to do with foundations.
Should I be worried about a crack above my window?
It usually means the lintel is failing — a decayed timber bressummer, a dropped brick arch, or a corroded steel lintel expanding as it rusts. It is a contained repair: prop, cut out, and replace with a correctly sized lintel bearing properly at each end. It is not a foundation problem.
Should I cut down the tree near my house?
Not automatically, and not without advice. On clay, removing a mature tree can cause heave as the ground rehydrates, which can do more damage than the shrinkage it was causing. The tree may also be protected. Get an engineer's and an arboriculturist's view before felling.
Measure it before you act
We photograph, gauge and date cracks on a first visit, so the next visit shows whether anything is actually moving. Free survey across Coventry.