The presence of small cracks in block walls and brickwork is not usually something to be too concerned about. We look at the limits of what cracking should be considered acceptable and when your home might require building repairs or an assessment from a property professional.
There are a number of reasons for brick or concrete block walls to develop cracks, and perhaps the most concerning of these for the home owner are subsidence or movement in the foundations. However, there are several reasons why cracks might appear in a building, some more serious than others:
- Ground movement as a result of clay shrinkage, settlement, land slip, vibration, subsidence, etc;
- Failure of the foundations;
- Moisture changes that cause the building materials to expand or contract, for instance sustained periods of dry weather or heavy rainfall;
- Thermal changes;
- Excess load;
- Tree roots (including trees being removed);
- Lack of suitable foundations (particularly in older properties);
- Alterations to the building or neighbouring properties.
What degree of cracking requires action?
In 2014, the Building Research Establishment (BRE) assessed a sample of 130 low-rise buildings which led to the identification of six categories of cracking under BRE Digest 251: Assessment of damage in low-rise buildings. The research identified what might cause the level of damage and what steps you might need to take to remedy the situation.
The first three categories of cracking (categories 0, 1, 2) were considered simply to be “aesthetic” issues, that generally only require redecoration:
0 – Hairline cracks less than 0.1mm: Hairline cracks are classed as negligible.
1 – Fine cracks of up to 1mm: Fine cracks can be treated easily using normal decoration. Damage that is generally restricted to internal wall finishes; cracks rarely visible in external brickwork.
2 – Crack widths up to 5mm: Cracks easily filled. Recurrent cracks can be masked by suitable linings. Cracks not necessarily visible externally; some external repointing may be required to ensure weather-tightness. Doors and windows may stick slightly and require easing and adjusting.
Categories 3 and 4 should generally be regarded as “serviceability” issues, which might affect the weather-tightness of the building or the operation of doors and windows:
3 – Crack widths of 5mm to 15mm (or several of e.g. 3mm): Cracks that require some opening up and can be patched by a mason. Repointing of external brickwork and possibly a small around of brickwork to be replaced. Doors and windows sticking. Service pipes may fracture. Weather-tightness often impaired.
4 – Crack widths 15mm to 25mm. Extensive damage which requires breaking-out and replacing sections of walls, especially over doors and windows. Windows and door frames distorted, floor sloping noticeably. Walls leaning or bulging noticeably, some loss of bearing in beams. Service pipes disrupted. Typical crack widths are 15mm to 25mm, but also depends on number of cracks.
Category 5 is considered a “stability” issue which would be likely to require structural intervention:
5 – Structural damage, cracks greater than 25mm. Structural damage that requires a major repair job, involving partial or complete rebuilding. Beams lose bearing, walls lean badly and require shoring. Windows broken with distortion. Danger of instability. Typical crack widths are greater than 25mm, but depends on number of cracks.
An independent Chartered Surveyor can inspect your property to assess the level of cracking in your home and advise you on the best method of dealing with the issue.