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Date posted: 15/01/2021

Assessing cracks in your building

Assessing cracks in your building

Most properties will experience cracks in the walls at some point. In older houses, temperature changes and humidity levels can cause walls to swell. Equally, in new premises, cracks can easily develop as the foundations settle and plaster dries out. 

It is important to be able to identify cracks should they occur and whether you need to worry about them or not.

The BRE (Building Research Establishment) produced a useful crack classification guide, which gives guidance on the types of cracks:


  • Less than 0.1mm wide (Hairline)

These are negligible - no action is required.


  • 0.1mm to 1mm wide (Very slight)

These can be treated easily using normal decoration. The damage is generally restricted to internal wall finishes; fine cracks are rarely visible in external brickwork.


  • 1.1mm to 5mm wide (Slight)

These cracks can be easily filled. Recurrent cracks can be masked by suitable linings.


Some external repointing may be required to ensure weather-tightness as the cracks are not necessarily visible externally. Doors and windows may stick slightly and require easing and adjusting.


  • 5.1mm to 15mm wide (Moderate)

These are cracks that require some opening up and can be patched. 


Repointing of external brickwork is usually required and possibly a small area of brickwork to be replaced. Doors and windows may experience sticking, service pipes may fracture and weather-tightness in the house is often impaired.


  • 15.1mm to 25mm wide (Severe)

Classed as extensive damage, these require breaking-out and replacing sections of walls, especially over doors and windows.


Windows and door frames are likely distorted, floor sloping noticeably. Walls may be leaning or bulging noticeably, with some loss of bearing in beams. Service pipes will be disrupted.


  • More than 25mm wide (Very severe)

Classed as structural damage, these cracks will require a major repair job, involving partial or complete rebuilding.


Beams will lose bearing and walls can lean badly and require shoring. There is a danger of instability in the house.


Overall, cracks up to 5mm in width are not a cause for concern - they are regarded as aesthetic issues that can be easily fixed with redecoration. Moderate and severe cracks will start to affect the weather-tightness of your home and the operation of doors and windows. Very severe cracks will likely require structural intervention, as they present major stability issues.


If you have cause for concern about significant cracks in your home, please contact DMP on 01482 623955. Our team of chartered building surveyors are experienced and will be able to assess the situation, offer trusted advice and give you peace of mind.