When to Call a Structural Engineer for Cracks in Walls
7/28/20265 min read
Cracks in Walls: When Should You Call a Structural Engineer?
Cracks in walls are common in homes across London and the wider UK. Some result from normal drying, seasonal movement or minor temperature changes. Others may indicate movement in the structure or foundations.
The challenge is knowing which cracks can be repaired during decoration and which need professional assessment. Width matters, but so do the crack’s position, direction, age and whether it is continuing to grow.
Are All Wall Cracks Structural?
No. Fine cracks can appear as new plaster dries, where different materials meet, along plasterboard joints or after minor settlement in a recently completed extension.
Thermal movement can also cause cracking. Materials expand and contract as temperatures change, particularly where internal and external walls meet or around ceilings and openings. NHBC guidance recognises that minor cracks can occur as a home dries and its materials adjust.
A cosmetic crack is usually fine, stable and limited to the surface finish. Structural cracking is different. It may indicate movement in the masonry, foundations, floors, roof or other load-bearing parts of the property. Approved Document A covers the structural stability of foundations, walls, floors, roofs and chimneys.
Warning Signs That Need Professional Attention
Consider arranging a structural inspection when a crack:
is getting longer or wider;
appears suddenly without an obvious reason;
runs diagonally from a door or window;
continues through brickwork or blockwork;
is visible in a similar position inside and outside;
is accompanied by bulging or leaning walls;
reopens soon after repair;
appears after structural alterations or nearby construction;
occurs with sticking doors, uneven floors or distorted windows.
Diagonal cracks around doors and windows, combined with difficulty opening or closing them, can be signs of subsidence or other movement. The Institution of Structural Engineers identifies these as warning signs that should be investigated by an experienced professional.
Seek urgent advice if a wall appears unstable, masonry is loose, a ceiling is noticeably sagging, or the structure has shifted after an impact, fire, flood or major building work. Keep people away from the affected area until it has been assessed.
Common Causes of Cracks in Walls
Drying and Shrinkage
Plaster, concrete, timber and masonry contain moisture when installed. As they dry, they can shrink slightly, causing fine cracks in new homes, extensions and newly plastered rooms.
Thermal Movement
External walls experience changing temperatures throughout the year. Repeated expansion and contraction can produce cracks where materials with different movement characteristics meet.
Settlement
A building may settle slightly as the ground and construction materials adjust to new loads. Minor settlement is not necessarily the same as ongoing subsidence, although the pattern and timing should be assessed when there is uncertainty.
Subsidence
Subsidence is the downward movement of the ground supporting the foundations. Possible causes include shrinkable clay, leaking drains, nearby trees, poorly compacted ground or historic ground disturbance.
RICS advises that fewer than 5% of properties affected by subsidence require underpinning. The cause of the movement should therefore be properly diagnosed before expensive or disruptive remedial work is considered.
Structural Alterations
Removing a load-bearing wall, forming a large opening, altering a chimney breast or completing a loft conversion changes how loads travel through the building.
Cracks may develop if a replacement beam, bearing, connection or temporary support is inadequate. They may appear above an opening, close to the end of a steel beam or in the walls and ceilings of the rooms above.
Cracking following structural work should not be dismissed as normal decoration damage without first checking that the new support has been properly designed and installed.
Deterioration of Building Materials
Corroding steel lintels, wall ties or embedded steelwork can expand and force masonry apart. Water penetration, timber decay and prolonged damp may also weaken building elements and contribute to movement.
Horizontal cracking above windows and doors can sometimes be associated with lintel deterioration, while cracking or bulging across a larger wall area may require investigation of wall ties or other restraints.
Nearby Construction Work
Excavation for an extension, basement or drainage installation may affect the ground supporting an existing wall. Vibration or inadequate temporary support can also cause local movement.
Cracking that starts during nearby construction should be photographed and investigated promptly. Record when it appeared and whether the neighbouring work involved excavation, demolition, piling or structural alterations.
What Will a Structural Engineer Do?
A structural engineer will usually begin by asking when the cracks appeared, whether they have changed and whether any construction, drainage or tree-related issues are known.
Previous drawings, photographs, structural reports, insurance records and details of earlier alterations can be helpful. The age and construction of the property will also be considered.
During an inspection, the engineer may examine:
the direction and pattern of the cracks;
the condition and alignment of the walls;
doors, windows and structural openings;
floors and ceilings;
the roof structure;
visible beams, columns and lintels;
accessible foundations or subfloor areas;
signs of moisture or defective drainage;
movement elsewhere in the property.
The cracking may be diagnosed as cosmetic and suitable for normal repair. Alternatively, monitoring may be recommended to establish whether movement is active.
Further investigation could include trial pits, a drainage survey, level monitoring, soil testing, crack monitoring or opening-up works to expose concealed structural elements.
Where a structural defect is identified, the engineer can recommend a proportionate repair. This might involve masonry repair, crack stitching, replacing a lintel, improving wall restraint, repairing drainage or strengthening a floor or roof.
Structural engineers can also produce calculations and drawings for beams, columns, foundations and other load-bearing elements where Building Control approval is required.
Monitor a Crack
Take clear photographs from the same position and include a ruler or another suitable scale. Record the date and lightly mark the ends of the crack with a pencil.
Check the crack periodically rather than relying on memory. Keep a simple record of any change in its width, length or appearance. Also note whether nearby doors and windows have become more difficult to operate.
Do not repeatedly fill and repaint the crack before its cause is understood, as this may hide useful evidence. A crack gauge can help record movement, but its readings must be considered alongside the building’s construction and the wider pattern of damage.
Where subsidence is suspected, speak to your buildings insurer before arranging major investigations or repairs. The insurer may have a specific claims procedure and may appoint its own surveyor or structural engineer. The Institution of Structural Engineers recommends contacting the insurer as an early step where subsidence may be involved.
Call a Structural Engineer
Call a structural engineer when a crack is progressive, unexplained, extends through structural masonry, appears with distortion elsewhere or follows work affecting a load-bearing element.
An early assessment can prevent unsuitable repairs and provide reassurance when the cracking is harmless. It may also identify a relatively simple problem—such as a defective lintel or leaking drain—before it causes more extensive damage.
A structural inspection does not automatically lead to major strengthening or underpinning. In many cases, the most useful outcome is a clear diagnosis and a practical, proportionate repair plan.
Reno Consulting provides structural inspections and engineering advice for residential properties across London. If you have discovered cracking in a wall, ceiling, extension or around a structural opening, our engineers can assess the likely cause, identify whether further investigation is required and recommend the next practical step.
