In case you hadn't noticed, it's the height of summer – the time of year when warmer temperatures and drying ground often lead to subsidence. But given all the rain, might households be off the hook this year? Not necessarily: in 2007, one of the wettest summers on record, the Association of British Insurers (ABI) reported that its members would have to pay out £162m covering 31,895 subsidence claims.
A surveyor would define subsidence as the downward movement of the ground supporting a building, with particular problems occurring when that movement varies from one part of the building to another, producing cracks.
Homeowners who discovers subsidence may wish the ground would swallow them up, as it can take up to three years to resolve the problem even with helpful insurers. And if the cover is void for any reason, it could end up costing tens of thousands of pounds to correct.
The three main causes of subsidence are the underlying soil, the age of the house and the proximity of trees or shrubs.
Tony Fisher at the Building Research Establishment says: "The shrinkage and swelling of clay soils is the single most common cause of movement in relation to low-rise buildings."
Houses built before 1965 tend to have shallow foundations and so are more prone to being affected by subsidence. Yet trees re- moving water from under the foundations are what actually cause the clay to shrink. Figures from Halifax Home Insurance show that 60 to 70 per cent of valid claims for subsidence involve trees.
Another cause of subsidence is damaged drains, softening or washing away the soil under foundations.
"Subsidence mainly occurs south of a line between the Wash and the Severn," says Mr Fisher, "with the London area particularly prone as it has a large number of houses."
Cracks are usually the first warning signs, although most buildings have some cracks due to the natural expansion and contraction of bricks caused by changes in temperature. What you should look for are small, usually diagonal, cracks – especially around doors and windows. These will usually be thicker than a 10p coin and wider at the top.
There are some simple measures that can be taken to minimise the risk of subsidence. First, drains and pipes should be checked regularly to ensure there are no blockages or leaks. Second, trees should be pruned occasionally to reduce water uptake, and any new trees or shrubs should be planted at a safe distance from a property.
If, despite your best efforts, you suspect you may have subsidence, what should you do? The ABI says: "As soon as you believe there may be a problem, you should contact your building's insurer. A policy will normally require the insurer to be advised of any potential claim as soon as possible. That is sensible in any event because the sooner the problem is investigated, the quicker everything can be put right."
However, this is not the view of Roy Ilott, spokes- man for the Royal Institution of Chartered Surveyors: "If you are not sure about the cracks, it is best, in the first instance, to get hold of a building surveyor, who can give you some independent advice.
He adds: "In my experience, insurers are only going to remedy damage that has already been caused, and are not interested in carrying out preventive work."
If the subsidence is caused by a tree, this can often be remedied by cutting it back so less water is extracted from the soil. But if the house has been severely affected, it may require underpinning – the deepening of the building's foundations.
It can take a long time to deal with bad cases of subsidence as the cracks may need to be monitored for a year by the insurer and only then will remedial work be carried out.
If you do have to make an insurance claim, there is usually a policy excess to be paid – often of around £1,000, according to Halifax Home Insurance.
All buildings policies differ in the extent of cover they provide, so check the small print and exclusions relating to subsidence. Don't, assume, for example, that outbuildings such as garages will automatically be covered.
Neil Curling, senior structural claims manager at Halifax Home Insurance, says premiums may increase if a claim is made. He also points out that any failure to disclose "material facts", such as a history of subsidence at a property or signs of cracking or bulging walls, could lead to the policy being declared void.
Russell Conway, a partner at Oliver Fisher Solicitors in London, comments: "Insurers will do everything they can to avoid paying out for subsidence as it often costs a five-figure sum to correct. We regularly get involved in trying to enforce policies as insurers try to slide out of them."
For those buying a property, Mr Ilott advises: "Have a full structural survey carried out as it will provide more time for the investigation of existing cracks."
Mr Conway agrees: "Never, ever buy anything without a full survey." He warns that searches won't necessarily pick up subsidence as the seller's solicitor can avoid providing a straight answer. "There is an art in giving replies to preliminary enquiries."
If a survey does reveal subsidence, obtaining buildings cover will be very hard.
A spokesperson for Nationwide Home Insurance confirms: "If subsidence occurs to an existing customer, we will continue to insure them. We will also provide cover to a new owner of the property subject to a satisfactory application. As is standard in the industry, we do not offer new policies to properties that have previously suffered from subsidence and not been insured with us."
'Our insurer spent £60,000 underpinning the house'
Paddy Boyle and his partner Jackie Summerfield own a Victorian house in the seaside town of Hastings, East Sussex. They were living there as tenants 10 years ago when the landlord found it was suffering from subsidence.
"We actually sat in on the talks between the structural engineer and the loss adjuster who was working on behalf of the insurer," Paddy recalls. "The engineer wanted extensive underpinning but the loss adjuster decided it was only necessary to underpin the bay window."
The landlord's insurer paid for the work and Paddy and Jackie bought the house shortly after.
Everything was fine until about two years ago, when a horizontal crack appeared in the living room. "We contacted the original structural engineer and our insurer, Zurich. We had to pay the £1,000 policy excess and Zurich spent about £60,000 underpinning the house," says Paddy. "It took about five months to complete and redecorate but we're very happy with it."
Hastings is built on clay soil and this is slowly drying out and causing shrinkage. "There has been no problem renewing our cover with Zurich," adds Paddy, "but other insurers have backed off when we've told them the house has been underpinned."