Specialist underpinning contractors and consultants have had their work cut out in recent times as varying weather patterns have impacted badly on ground conditions. Many report that enquiries from householders continue to rise as increases in rainfall followed by sustained dry periods weaken soil strata, leading to subsidence.
Abbey Pynford's marketing manager Andrew Tear says the demand for underpinning is traditionally weather driven. 'Over the last three or four years we have had fairly dry summers and as a result we have been busy.
'When we experience sustained periods of rain the demand dips slightly because increased moisture in the ground helps to stabilise buildings. When this happens the problem of unstable properties does not usually get any worse, but it does not get any better either,' he said.
Exterior brickwork is one of the first indicators that subsidence is affecting the property. Cracks running through mortar or through the bricks themselves are two common telltale signs that the ground on which the building stands is not firm.
Soil type is also an important factor in the stability of buildings. A deficit in rainfall can often lead to subsidence in clay, whereas granular material is loose in the ground and does not usually react so heavily to a reduction in moisture.
Force Foundations' director Mark Cogan says: 'A common scenario occurs after a dry summer when small cracks up to half an inch wide appear in brickwork, usually due to moisture depletion in clay soils. The cracks might close up again in the winter and may reopen the next summer if it is very
dry. In extreme cases, this opening and closing can weaken the brickwork or structure severely.'
Such cracks often go unnoticed. If they are found, homeowners should be encouraged not to ignore the problem but to make enquiries, Cogan says. 'Obvious deterioration to brickwork is a cause for concern and a structural engineer should be contacted as soon as possible. A problem which is left over many years can be much more costly to rectify.'
Consultant Nicholson Jones Partnership says it is important to determine the effect subsidence has had on a property thoroughly before specifying a solution. 'The majority of our work involves partial under- pinning using mini-piles because subsidence problems are usually localised. If used correctly, mini-piling can be as reliable a solution as traditional mass concrete underpinning and is considerably more economic,' says partner Mike Catris.
Payment for nearly all underpinning work comes from insurance companies, which are often alerted by loss adjustors when the customer has one plan in mind - to sell their house. 'Insurance companies pay for 95% of domestic underpinning and between 15% and 20% of underpinning takes place when a house is being bought or sold.
'A buoyant housing market usually stimulates further activity as problems which homeowners may not have been aware of come to light,' said Catris.
Once a problem has been reported, a house is usually monitored over a period of six months by an independent structural engineer which will analyse the rate of movement. In the usual course of events, the engineer and a quantity surveyor pass their findings on to a loss adjuster, who then draws up a report. Insurance companies are then contacted for authorisation to begin remedial work.
This chain of events is widely regarded as a necessity but it is time consuming and can cause reimbursement problems to contractors, for example, if they are engaged at an early stage. Abbey Pynford's Andrew Tear says: 'Monitoring is seen as a low cost measure, to analyse what actually needs to be done and make sure that underpinning is the right solution. 'As the process involves many different parties, it is often long and drawn out, with some claims not coming to fruition for a year or more.'
Charterhouse Underpinning's managing director Charles Dixon says a more streamlined process could be of benefit to the customer. 'Payments from insurance companies need to be faster, but there is often a delay if they are inundated with claims.
'As a contractor you are carrying costs on a contract which can take some considerable time to complete. Those costs have to be covered. If the payment process was quicker, costs would fall. Everyone involved in a claims procedure needs to be made more aware that greater co-operation between each other could lead to a fall in the final cost,' says Dixon.
'It is important to determine the effect subsidence has had on a property thoroughly before specifying a solution. '