Diagnosis without foundation?: Roger Trapp talks to an engineer who wants a rethink on subsidence claims

MILLIONS of pounds are being wasted every year in unnecessary underpinning because of misdiagnosed subsidence, an engineer claims.

Nick Maclean, a civil and structural engineer who has spent nearly 20 years investigating defects in commercial and domestic buildings, has written to 11 insurance companies calling for a change of approach. But nine months later he has received no response.

'In recent months I have been asked to look at a number of buildings in the South-east which have suffered from cracking and where the assumption by owners, surveyors and engineers is that foundation subsidence is the cause of the problem. However, in an alarmingly significant number of cases subsidence clearly has been only a small contributor to the cracking and in some cases not a factor at all,' he said.

Nevertheless, underpinning is still being carried out - sometimes for a second time. In one case, at a terraced house in north London, there have been three insurance claims for subsidence in six years.

Mr Maclean, who has spent 20 years with the consulting engineers Ove Arup & Partners, believes a 'subsidence bandwagon' has started to roll, with everybody jumping on it because it was originally the most convenient short-term way of dealing with cracks in buildings.

The householder complained about a crack, a surveyor or engineer decided it was caused by subsidence, the insurer paid up, the work was done and the householder moved on, unaware that the problem was recurring later.

Now that claims are running at more than pounds 1bn a year, insurers are more reluctant to pay out. Excesses of pounds 1,000 and higher premiums are the norm, and certain postcodes are rated danger areas. But there is no apparent willingness to take a fresh look at the problem, said Mr Maclean, who regards the postcode policy as ridiculous since geology does not follow such divisions.

Mr Maclean believes many of the problems are caused by thermal expansion resulting from excessive heat in hot summers that typically occur in the UK every 10 years. He says subsidence cracks develop more slowly than those caused by horizontal movement, where sudden movements can follow long periods of hot weather. 'I'm applying schoolboy physics, not engineering.'

In many cases, there is no need for remedial work because the buildings are in no danger of falling down. Instead, if the householder waits for a return to more normal temperatures the cracks will probably close up. If repairs are required, underpinning is not the answer. The correct action ranges from inserting metal rods to restrain bowed walls to rebuilding them.

He believes Victorian properties may be particularly susceptible because the front and back walls were erected first, with the internal partitioning only coming later. But he has also seen the problem in long lengths of brickwork that receive the full force of the sun.

'I have found an overwhelming understanding of the technical issues from reasonably intelligent lay people,' he said, 'but a great deal of understandable reluctance on the part of my colleague engineers and surveyors to accept that they have got it wrong.'

Commercial Union, one of the insurers contacted by Mr Maclean last September, would not comment on the technicalities of subsidence claims, other than that it relied on expert evidence from surveyors and engineers.

CU's figures for the first quarter of this year - showing the number of insurance claims down 11 per cent and the value down 42 per cent at pounds 2.7m compared with the same period last year - suggest a continuing downward trend, thought to be largely due to the return to a wet, cool climate.

A spokesman for another insurer had no recollection of receiving a letter from Mr Maclean, but said the company received many suggestions for dealing with house damage claims. Both insurers said they had learned a lot about subsidence since the summer of 1976.

(Photograph omitted)