When Is Cracking in a House Structural?
Published: 30 September 2026
By Joseph Lawson MEng (Hons), Director / Structural Engineer, Lawson Cook Limited
Cracks in walls and ceilings are common in residential properties and do not automatically indicate a serious structural problem. Buildings naturally move over time due to changes in temperature, moisture, materials and normal settlement.
However, the location, width, direction and progression of cracking can sometimes indicate movement within the structure that warrants further investigation.
At Lawson Cook Limited, we regularly inspect properties across Hertfordshire where homeowners or purchasers are concerned about cracking. This guide explains some of the signs we look for when determining whether cracking may be structurally significant.
Does Cracking Always Mean There Is a Structural Problem?
No.
Fine cracking can develop for many relatively minor reasons, including:
Drying shrinkage of plaster and other finishes
Thermal movement
Minor settlement following construction
Movement between different building materials
Changes in moisture content within timber
Previous alterations to the property
The appearance of a crack alone is therefore not enough to determine its significance.
A structural assessment considers the cracking alongside the construction of the building, its location, surrounding defects and any evidence that movement is ongoing.
What Types of Cracking Can Be More Concerning?
Some cracking patterns can warrant closer investigation.
Stepped Cracking Through Brickwork
Diagonal or stepped cracking following the mortar joints within external brickwork can indicate differential movement within the wall or its foundations.
The cause can vary considerably and may include foundation movement, nearby vegetation, drainage problems, alterations to the building or localised structural defects.
The cracking pattern needs to be considered alongside the wider building before conclusions are reached.
Diagonal Cracking Around Windows and Doors
Cracking extending diagonally from the corners of window or door openings can sometimes be associated with movement of the surrounding masonry.
However, it may also relate to lintels, thermal movement or differences in construction.
The condition of the lintel and masonry above the opening should therefore be considered as part of the assessment.
Cracks That Continue Through Several Materials
A crack that continues through plaster, masonry and external finishes can be more significant than superficial cracking restricted to plaster alone.
This can indicate that movement has occurred within the underlying structure rather than solely within the decorative finishes.
Cracking Accompanied by Distortion
Cracking becomes more significant when accompanied by other symptoms such as:
Doors or windows becoming difficult to open
Sloping or distorted floors
Noticeable movement around openings
Bulging or leaning masonry
Separation between walls and ceilings
Movement between an extension and the original building
The combination of symptoms is often more informative than the crack width in isolation.
Does the Width of a Crack Matter?
Crack width is useful information, but it should not be considered on its own.
A narrow crack in a structurally important location may warrant investigation, while a wider crack in a plaster finish may have relatively little structural significance.
During a structural survey, we therefore consider the crack width together with:
Crack pattern and direction
Location within the building
Construction type
Building age
Previous alterations
Foundation arrangement where known
Nearby trees and vegetation
Drainage
Changes in ground level
Evidence of previous repairs
Whether movement appears historic or progressive
Are Cracks Worse on Clay Soils?
Properties founded on shrinkable clay can be more susceptible to ground movement where soil moisture levels change.
Trees and other substantial vegetation can influence moisture within clay soils, while leaking drainage can also affect local ground conditions.
However, the presence of clay soil or nearby trees does not automatically mean that cracking is caused by subsidence.
The relationship between the cracking, foundations, ground conditions, vegetation and drainage needs to be considered before reaching a conclusion.
How Can You Tell Whether a Crack Is Still Moving?
This is not always possible from a single inspection.
Signs such as clean fracture surfaces, recently damaged decorations or changes reported by the occupants can provide useful information, but sometimes monitoring is required.
Depending on the circumstances, recommendations may include:
Monitoring crack widths over time
Inspecting drainage
Trial holes to establish foundation construction
Ground investigation
Arboricultural advice
Opening-up works
Reviewing previous photographs or survey reports
Further investigation should be proportionate to the nature and severity of the movement observed.
What Does a Structural Engineer Look for During a Crack Survey?
Our structural surveys are normally visual and non-intrusive unless otherwise agreed.
We assess the visible cracking together with the construction and behaviour of the building. This typically includes reviewing:
External elevations
Internal cracking
Doors and windows
Floors and ceilings
Roof structure where accessible
Extensions and structural alterations
Nearby trees and vegetation
Visible drainage features
Local ground conditions
Previous repairs where apparent
Where the cause cannot reasonably be established from the visible evidence, we identify any further investigations that may be necessary.
Should I Have Cracking Inspected Before Buying a Property?
If a building survey, mortgage valuation or your own inspection identifies potentially significant cracking, obtaining structural advice before completing the purchase can help clarify the likely significance and any further investigations or repairs that may be required.
Where you have already received a building survey report, providing this to the structural engineer before the inspection can also help focus the assessment on the concerns that have been raised.
When Should You Contact a Structural Engineer?
Structural advice should be considered where cracking is:
New or noticeably worsening
Significant in width
Diagonal or stepped through masonry
Present both internally and externally
Associated with distortion of the building
Concentrated around an extension or previous alteration
Accompanied by sticking doors or windows
Identified as a concern within a building survey or mortgage report
If you are unsure, photographs can often help establish whether a structural inspection is appropriate.
Structural Crack Surveys in Hertfordshire
Lawson Cook Limited is a structural engineering practice based in Hertford. We undertake structural surveys and reporting for homeowners, property purchasers and property professionals throughout Hertfordshire and surrounding areas.
Our work regularly includes the assessment of cracking, structural movement, suspected subsidence, alterations to existing buildings and other structural concerns.
If you are concerned about cracking to a property, please send us:
The property address
Photographs of the cracking
Any estate agent floor plans available
Any relevant building survey or previous structural reports
We can then advise on the appropriate next steps and provide a quotation for a site survey and reporting.
Lawson Cook Limited
Structural Engineers
Hertford, Hertfordshire
info@lawsoncook.co.uk
www.lawsoncook.co.uk