When should you worry about a crack? Peter French discusses

Written by Peter French.

We all have very different thresholds when comes to what we would describe as painful. This is very much the case when people discover cracking within their property. One person’s minor crack is another’s major defect.

Firstly however, we should consider the question of what causes buildings to crack. Crack damage occurs when the fabric experiences stresses which the material cannot sustain. The fabric, often masonry, then breaks, forming cracks. If the forces applied to the structure continue, the crack may  increase in width. What might be the cause for these forces? The causes can include foundation movement, settlement or subsidence, a lack of lateral restraint to walls, roof spread, thermal movement or shrinkage.

In recently constructed properties the cause may well be due to shrinkage as part of the drying out of the property, alternatively there is the possibility of settlement of the foundations.

In properties of greater age the foundation movement could be due to subsidence. The subsidence can be the result of a number of causes; examples of which include leakage from below ground drainage or water mains, clay shrinkage or soil movements due to geological features. These causes can lead to what’s described as progressive movement, that is to say the cracks continue to get wider.

Subsidence damage will generally have a similar pattern. The cracking will be diagonal sometimes following brick and blockwork courses. Widths will vary, often wider at higher level reducing in width towards ground level. Diagonal cracking can appear above openings where lintels have either deflected or failed, so diagonal cracking can be an indication of something significant and therefore should not be ignored. Crack damage as a result of roof spread will generally be apparent by cracking at high level and usually horizontal. If walls are not tied into the structure as a whole this can lead to lateral movement. The lack of a lateral restraint to external walls can result in vertical cracking at the junction with partitions connected to an outside wall and may be apparent by a gap between floorboards and skirting boards for example. These problems may be old and not progressive. Shrinkage cracking due to thermal movement is generally internal and would not normally be considered as being structurally insignificant within a domestic property. However, they are a nuisance aesthetically. These cracks are often vertical. These types of cracks often occur where two different building materials meet. They can generally be dealt with during the normal course redecoration.

Peter French, managing director of Canham Consulting, is on 01603 430650.

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