Warm weather raises the risk of earth movements

Summer is subsidence season. With hotter weather and less moisture in the soil, thousands of households across Britain will be seeing telltale cracks appearing around their windows and door frames. Repairs cost £7,000 or more on average, so it's essential you be insured.

Subsidence is the downward movement of the load-bearing soil on which a structure sits. Houses built before 1965 are particularly susceptible to it as their foundations will not have been dug as deeply as more modern properties. Subsidence is a costly business for insurers. Last year, 27,707 individual claims paid out a total of £137m to cover repair costs. "Subsidence is an insurer's nightmare," says John Sellers, a spokesman for insurer More Than. "The work to remedy it is time consuming and claims frequently cost in the tens of thousands."

Problems with subsidence are most common in the South-east and parts of the Midlands due to clay sub-soils that expand and contract depending on how much water is in the ground. London is particularly affected because of the high concentration of properties and concrete foundations making it more difficult for moisture to circulate underground. The other main culprits in subsidence cases are trees, which, according to figures from insurer Royal & Sun Alliance, are the cause of problems in between 60 and 70 per cent of valid subsidence claims. Trees absorb water in clay soils, causing them to contract. And if planted too close to houses, as is often the case in London and other big cities, the roots can grow underneath the property and undermine the foundations. Other causes are damaged or blocked drains leaking water that washes away soil with a high sand content under the foundations, and man-made excavations of soil during building work that cause problems later on.

The warning signs of subsidence are cracks in walls, often around window and door frames down to the floor, that are thicker than a ten pence piece. Cracks tend to go diagonally and there is rarely a uniform gap all the way down, it will often be narrower at the bottom. As soon as you notice cracks you need to contact your insurer which will send out a loss adjuster. Malcolm Tarling, a spokesman for the Association of British Insurers, says, "If you have a subsidence claim the insurer will not rush in. It will employ a chartered surveyor to monitor over a period of time what the movement is and ascertain what is causing the problem. You need to get the correct diagnosis in order to take the correct course of action." This can be frustrating for homeowners, and insurers have been known to stall and even try to get out of paying up if the damage is substantial. "It might feel as if nothing much is happening to begin with," says Mr. Sellers. "But in the early stages, there needs to be a certain amount of monitoring to see if the situation is deteriorating or stabilising."

Jonathan Smithers, a property spokesman for the Law Society, agrees. "I haven't come across any incidences when insurers have not paid up. However, where there are likely to be big and ongoing claims, they certainly look closely at the original insurance contract that was entered into. If there are wrongly answered questions on the proposal the contract can be void." It is essential that you disclose all information about previous subsidence problems and, if necessary, get your cover from a specialist insurer.

But even when claimants are completely honest and up front, subsidence claims can drag on and on. "Our claim stretched over about three years as the insurer could not decide upon exactly how much work was necessary," said Margaret Town, a homeowner from west London. "We received tenders ranging from a few thousand up to £40,000. Eventually, though, the insurer decided that it was necessary to do work in only two rooms. All in all, it was an incredibly long-winded process".

If you haven't had any previous history of subsidence, all standard household insurance policies should cover you, but the usual industry excess sits at £1,000. If the remedy for the subsidence is fairly straightforward – you might, for example, just need to remove a tree planted too close to your property – then the work may cost less. Although subsidence is covered as standard, you will also need to check the small print to see exactly what work and repairs are included and up to what amount.

For those properties with a history of subsidence the outlook is less clear. "Property that has a history of subsidence is not necessarily uninsurable," says Mr Tarling. "Premiums may be more costly, but it depends on when the subsidence occurred and why." There is a general agreement across the insurance market that once a property has suffered from subsidence, its current insurer is obliged to continue to cover it, even if it is sold on to another buyer.

"The theory is that it should make things simpler for the home owner," says Mr Sellers. "If work was done five years ago and then cracks appear, the insurer will know the history. It makes any further work needed much easier." However, although the insurer is obliged to insure your property, you don't have to stick with them. But, comparing prices when your home has a history of subsidence is a long process as you will have to contact each insurer directly. Gordon Maw, a spokesman for comparison site Gocompare.com, says, "Subsidence is such a scary issue that you often have to talk directly to your insurer to get the cover you need." It's important not to just jump at the cheapest price. As Mr Smithers says, "Make sure you will be fully covered. Simply going for the cheapest quote on the web may result in much bigger costs later on."

If you'd prefer to avoid a long, drawn-out insurance claim, you can take some preventative measures. We can't control the weather, but making sure drains are cleared and pruning trees in close proximity to the house can reduce the chances of your property subsiding. Avoid new planting close to your house.

If you are buying a property, you need to keep a keen eye out for any form of cracking. "If you do spot anything in a property you would like to buy," says Alan Cripps, a spokesman for the Royal Institute of Chartered Surveyors, "refer it to a surveyor to give you an assessment. You could be buying into a major problem."