More than the eye can see
An interesting - and little known - statistic is that the average Victorian semi is made up of around 40,000 individual elements, including bricks, timbers, tiles, pipes and wiring. Of these, only in the region of 10,000 are visible, so how can a building surveyor be certain about the extent of any problem when it's only possible to see a quarter of the building during a survey?
Training and experience are vital in this area as is modern equipment such as damp meters, thermal imaging and endoscopes. But there's one area where statistical analysis can also play a part, and that is in structural movement. The starting point for this is BRE Digest 251: Assessment of damage in low-rise buildings.
Following a study of 130 properties suffering from subsidence, five kinds of crack were identified, categorised primarily by width. In simple terms, the study found that categories 1 and 2 - cracks of less than 5mm - were essentially aesthetic problems and were therefore unlikely to indicate a significant structural issue. Cracks in categories 3 and 4 - cracks of between 5mm and 25mm - were found to cause serviceability issues, such as sticking doors or penetrating damp. Anything in category 5 - cracks of over 25mm - was considered to require structural intervention.
As experienced building surveyors, we know that if we see a 4mm crack, statistically speaking it will be safe, but of course statistics only take you so far. What if the crack has developed over a short space of time and is increasing in size? What if there are a lot of 4mm cracks? What are the chances that there are other cracks hidden in the three quarters of the building that are hidden from view? It is at this point that a building surveyor's skills, experience and judgement come in. If you know how the property is constructed, understand the nature of the sub-soil beneath the property and consider other additional factors, it's possible to figure out the likely cause of the cracks. A professional surveyor will then be able to make a judgement about the extent of any problem and advise on suitable next steps.
Anglian Home Surveyors are specialist building surveyors in Cambridge and Haverhill, so to book a building survey please call Raphael Stipic on 01223 661439 or complete our enquiry form.
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