Almost every building cracks. Most cracking is cosmetic, some of it is a sign of movement that has already stopped, and a small proportion indicates a structural problem that needs attention. This guide explains the factors that engineers consider when looking at cracking, how to record it usefully, and when it is sensible to arrange a targeted structural inspection. It does not attempt to diagnose cracking, because that cannot responsibly be done from a description or a photograph.
Cracking has many causes
Cracking is a symptom, not a diagnosis. The same crack pattern can arise from very different causes, and the significance of a crack depends far more on its context than on its size alone.
Common contributory factors include shrinkage of new materials, thermal movement, moisture movement, differential movement between materials, deterioration of embedded components, overloading, previous alterations, and ground-related movement. Several of these frequently act together.
What an engineer looks at
Of these, change over time is often the most informative single factor. A wide crack that has not moved in twenty years is usually less concerning than a hairline crack that has doubled in three months.
- Location — which element is cracked, and where it sits in the load path
- Orientation — vertical, horizontal, diagonal or stepped cracking each suggest different mechanisms
- Width and taper — whether a crack is uniform or wider at one end
- Distribution — whether cracking is isolated or repeats through the building
- Change over time — whether the crack is stable, seasonal or progressive
- Correlation — whether cracking coincides with alterations, trees, drainage, or a change in construction
Finishes versus structural materials
It matters a great deal whether the crack is in plaster, render, a plasterboard joint, a screed, or in the structural masonry, concrete or timber behind it. Cracking to finishes is extremely common and frequently reflects nothing more than shrinkage, thermal movement or normal building tolerance.
Cracking that passes through masonry units, through mortar joints in a consistent pattern, or through structural concrete deserves closer attention, because it indicates movement in the structure itself rather than in the finish applied to it.
Movement, moisture and temperature
Buildings move. Materials expand and contract with temperature and moisture content, and different materials do so at different rates. Long unjointed runs of masonry, junctions between old and new construction, and interfaces between dissimilar materials are all predictable locations for cracking.
Moisture is a particularly common driver: leaking gutters and downpipes, defective flashings, blocked drainage, and persistent condensation can all cause localised movement and deterioration that appears as cracking. Establishing whether water is reaching the structure is often the most productive first step.
Alterations and deterioration
Cracking often appears after alterations, because the load path has been changed. Openings formed without adequate support, beams that deflect more than the surrounding finishes can tolerate, removed chimney breasts, and additional loading from new floors or plant can all produce cracking some time after the work was completed.
Deterioration is the other frequent cause. Corrosion of embedded steel — cavity wall ties, lintels, bressummers and reinforcement — is expansive, and typically produces characteristic horizontal or bed-joint cracking. Decay of timber bearings and degradation of poor-quality mortar produce their own patterns.
Ground-related movement as one possible consideration
Ground movement is frequently the first explanation people reach for, and it is one legitimate consideration among several. Shrinkable clay soils, nearby vegetation, seasonal moisture variation, leaking drainage, made ground and historic mining are all relevant in parts of the UK, including the North West.
However, ground-related movement should be a conclusion drawn from evidence, not an assumption. Establishing it normally requires a combination of inspection, monitoring, drainage investigation and, in some cases, ground investigation. Where an insurance claim may be involved, the process is usually managed by the insurer and their appointed specialists.
Monitoring
Where a crack's behaviour over time is the missing information, monitoring is often the most proportionate next step. This can range from simple dated photographs with a scale, through calibrated tell-tales, to precise level and displacement monitoring.
Monitoring periods normally need to span at least a full seasonal cycle to distinguish seasonal movement from progressive movement. That can feel slow, but reaching a reliable conclusion is generally preferable to undertaking remedial work that addresses the wrong mechanism.
Photographs and records worth keeping
- A wide photograph showing where the crack sits in the elevation or room
- A close photograph with a ruler or coin alongside for scale
- The date of each photograph, and a note of when the crack was first noticed
- Both faces of the wall where accessible, and the corresponding external elevation
- Photographs of nearby gutters, downpipes, drainage covers and vegetation
- Any previous reports, insurance correspondence or records of earlier repairs
When a targeted structural inspection may be appropriate
- Cracking that is visibly progressing, or that has appeared suddenly
- Cracking accompanied by doors or windows binding, or by sloping floors
- Cracking that passes through structural masonry, lintels or concrete
- Cracking that has followed recent alterations, or that is near a new opening
- Cracking identified in a survey during purchase, where a specific opinion is required
- Cracking in a commercial or industrial building where operations or occupancy are affected
Circumstances requiring more urgent attention
Some situations should not wait for a scheduled appointment. Signs of sudden or accelerating movement, visible deflection or sagging of a beam, floor or roof, displaced or bulging masonry, spalling concrete with exposed reinforcement, or any structural distress following an impact, fire, flood or excavation adjacent to the building all warrant immediate professional attention.
If there is any concern about immediate safety, the area should be vacated and emergency services or the local authority contacted before any inspection is arranged.
Key considerations
- Crack width alone is a poor indicator of significance; location, pattern and change over time matter more.
- Cracking cannot be responsibly diagnosed from a description or a photograph.
- Water ingress and drainage defects are among the most common underlying contributors.
- Monitoring across a full seasonal cycle is often the most proportionate next step.
- Sudden movement, visible deflection or displaced masonry require immediate attention.
Related BES tools and services
Related guidance
Preparing information about cracking or movement?
General guidance only goes so far. Describe your building and what you are planning, and you will receive project-specific advice from a Chartered Structural Engineer.
Important limitations
This publication provides general information only and does not constitute structural engineering advice, design or assessment. Project-specific engineering requirements should be established by an appropriately qualified structural engineer.
BES-TG-003 · Version 1.0 · Reviewed August 2026 · Next scheduled review August 2027