Assessing cracks in houses
Everyone is familiar with cracks in the brick or concrete block walls of houses. Rupert Pool explains how cracks in houses are assessed and what level of cracking is normal and to be expected.
What causes cracks in buildings.
Cracks in brick or concrete block walls can be caused by a number of factors. One of the most unnerving for the occupants in subsidence or foundation movement. Changes in the ground conditions under and around a house can cause it to move slightly, which can lead to cracks developing in the walls.
Historically, claims on household insurance policies for repairs to buildings after subsidence have increased after periods of very dry weather. This prompted the industry to look in detail at how cracks were assessed and what repair works were necessary.
How cracks are assessed
In order to help building surveyors to identify when ground movement had occurred and when structural intervention was necessary, BRE carried out an assessment of 130 properties that had suffered from subsidence.
The results of the study enabled a way of categorising cracks to be developed, which would help building surveyors and insurance assessors to determine whether the cracks were likely to affect the property – and what repairs were appropriate. The results of the study and the conclusions were published in BRE Digest 251 Assessment of damage in low-rise buildings.
Six categories of crack were identified, which linked the width and number of cracks to the type of repair that was appropriate.
When to consult a professional
In general, categories 0, 1, and 2 with crack widths up to 5mm can be regarded as ‘aesthetic’ issues that require only redecoration. Categories 3 and 4 can generally be regarded as ‘serviceability’ issues, that is, they affect the weather-tightness of the building and the operation of doors and windows. Category 5 presents ‘stability’ issues and is likely to require structural intervention.
It should be stressed that these comments are a simplification of the assessment needed to properly classify damage to housing. Several factors, including whether the widths of the cracks are increasing with time, can affect the classification. BRE Digest 251 should be consulted when carrying out any assessment and a building professional should be consulted where damage is significant.