When concrete and clay begin to crumble

Even though her conservatory seems to be making a bid for freedom, Jacqui Zinkin is trying to remain calm. When she returned home from holiday to Golders Green, north London, last July, she found that a gap of "about 20mm" had opened up between her much-loved conservatory and the rest of the house.

Even though her conservatory seems to be making a bid for freedom, Jacqui Zinkin is trying to remain calm. When she returned home from holiday to Golders Green, north London, last July, she found that a gap of "about 20mm" had opened up between her much-loved conservatory and the rest of the house.

"Part of the house upstairs is separating from downstairs, the floor has shifted and the conservatory is spinning off to the neighbours' garden," says Ms Zinkin. She has owned the property since 1992, but had never before found signs of subsidence.

Hers is not an isolated problem. A worry for homeowners and insurers alike, serious cracks in brickwork and plaster are becoming an all too familiar sight in homes across London and the South-east. The combination of last summer's heat wave and an unusually dry winter is playing havoc with clay soil, causing the ground beneath properties to move and leading to cracks in plaster and brickwork.

The problem of subsidence is no longer restricted to a handful of residents with period homes on clay soil. Ms Zinkin's house, which is built on clay, was constructed just after the Second World War. Royal & SunAlliance, the second largest provider of buildings and contents insurance in the UK, reports that claims for subsidence cost it more than £120m in 2003 - up from £50m the previous year.

One of the reasons Ms Zinkin isn't panicking is that her insurer, Legal & General, will cover the cost of sorting out her subsidence, as well as paying for her to stay in temporary accommodation while the work is carried out.

Some insurance brokers predict that the rise in subsidence claims could cause buildings insurance premiums to go up 10 per cent this year. But Richard Lowe, the head of general insurance at mortgage broker Savills Private Finance, says it is too early to put a figure on any increase.

"Last year we had all the conditions that lead to subsidence," he says. "But nobody knows how bad it will be until winter has finished."

Homeowners who find cracks suddenly appearing in their plaster or brickwork, particularly after dry weather, should notify their insurer. But remember that cracks are not always caused by subsidence: new properties take time to settle, and cracks often appear in the plaster as this happens. Telltale subsidence cracks tend to be found around door and window frames, and are usually diagonal.

Once notified, your insurer will arrange for a structural engineer to visit your home to check the type of soil it is built on, and the condition of the foundations. He or she will then make recommendations for rectifying the problem, and will also supervise the work when it is carried out.

There are no quick-fix solutions: Ms Zinkin's insurers are monitoring cracks and other signs of movement over a 12-month period to establish what is causing them. Only after this will a plan of action be drawn up.

In the past, subsidence was dealt with by underpinning the foundations, which involves strengthening or deepening them. But this is not done so much nowadays; the professional removal of trees and shrubs and localised repair to brickwork is insurers' first choice. "Underpinning can cause more problems than it solves," says Savills' Mr Lowe. "So problems are often monitored for one to two years before a decision is made on the type of repair required."

Trying to sell a home that is being monitored for subsidence is well nigh impossible, and such plans will have to be put on hold. "I can't imagine many mortgage lenders rushing to lend on a property that is subject to an ongoing claim for subsidence, or that many insurers will take it on," warns Malcolm Tarling of the Association of British Insurers.

But Mr Lowe says homeowners shouldn't think that they will never sell their property. "Provided the necessary work is done properly by a structural engineer, it should be a good risk for the next owner. A clean bill of health will be totally acceptable to a lender, and your insurer is duty bound to continue insuring the incoming purchaser."

Why your home can crack up

What is subsidence?

The downward movement of the ground beneath your home. Problems arise when movement varies from one part of the building to another.

What are the signs?

Small, usually diagonal, cracks, suddenly appear in the plaster indoors, and in bricks around doors and windows.

How can I reduce the risk?

Make sure trees and shrubs close to your property are pruned regularly. Check pipes for splits, and drains for blockages or leaks. Clear dirt and leaves from gutters.

Am I covered under my insurance?

Most buildings insurance covers damage caused by subsidence. You will have to pay the excess on any claim.

What happens if I recently changed insurer?

If a claim is made within eight weeks of the changeover, your previous insurer will deal with it under the Association of British Insurer's Domestic Subsidence Claim Handling Agreement. Claims made between eight weeks and a year will be handled by your new insurer with the cost shared by the two companies.

Source: ABI