There may be hundreds of thousands of properties which are damaged by last year's soil shrinkage subsidence, but as yet undiagnosed. The full picture will only emerge once the housing market picks up: most cases are only detected when a house is put up for sale and surveyed.
Subsidence is a particularly grim problem because its effects continue for years. A claim will probably take two years to process; the work can take months to complete; and the house may be subsequently unsaleable because of homebuyers' fears of the problem recurring. Indeed, many of the subsidence claims last year were for homes previously affected, and partially repaired, in the 1980s. Surveyors argue that insurers took short-sighted, ineffective and ultimately very expensive action when faced by earlier spates of claims. Only the immediately affected parts of a house were underpinned, leaving other sections to crack subsequently - as many did last year. Insurers often took action too quickly, before determining how severe the damage was.
"You need to be like a surgeon, and think long and hard before taking the knife," advises surveyor David Tuffin, of Tuffin, Ferraby and Taylor in London. "You can cause a lot of damage by taking action too early."
After subsidence work is carried out, a big increase in building insurance premiums is likely. This is unfair, argues the Subsidence Claims Advisory Bureau, because if effective action is taken a property is unlikely to be hit again. The bureau, working with Property Underwriting Services, offers a specialist scheme - Previously Underpinned Properties - backed by the US insurer, CNA International, for homeowners having difficulty obtaining insurance.
Property Underwriting Services also offers soil reports to homebuyers. These range from a basic report for pounds 12, which suggests susceptibility to subsidence (based on computer records of the area) to a site visit analysing a soil sample, at pounds 125. An associate company, Survey Sure, offers insurers and lenders access to Site Specific Underwriting Research, a database of assessed subsidence risk on each property in the country, compiled on a walk-by basis in conjunction with computer mapping.
Ventech Systems provides reports, based on computer records, of subsidence risk, which cost pounds 75 individually. A number of insurers, mortgage lenders and surveyors use the service. Water companies have also used the service to help plan their mains pipes replacement programme.
Chris Venvell, managing director of Ventech, says subsidence caused by soil shrinkage is now expanding out of its traditional southern England area and moving north. He also predicts that as more insurers use detailed survey information, so premium differentials will grow markedly, with susceptible properties costing as much as pounds 3,000 a year to insure. But Chris Jordan at the Subsidence Claims Advisory Bureau says the effects on premiums will be mitigated by fear of losing business: "The market is very competitive, as a result of direct marketing. Insurers won't go overboard on high-risk homes." And, he adds, they will become cheaper on low-risk properties.
q Subsidence Claims Advisory Bureau and Property Underwriting Services 01424 733727, Ventech Systems 01789 488707.
Getting to the source of the problem
The home owner is not necessarily a powerless victim of forces beneath the soil. The Buildings Research Establishment reports that 79 per cent of subsidence incidents are at least partly due to trees too near a property.
The traditional rule of thumb is that a tree should not be planted nearer to a building than one-and-a-half times its own full-grown height. But a study conducted for the Subsidence Claims Advisory Bureau shows that this is an incomplete guide. Broad-leafed trees are more of a problem than evergreens, and while a yew might be acceptable five metres away from a house, a willow should not be planted within 40 metres of a property.
Once a tree is there, though, killing it can cause more damage than keeping it. If a well-established tree is removed the soil may expand, or heave, and this may cause considerable damage to foundations. A tree specialist should be engaged for advice before any action is taken. It may be necessary to prune either roots or branches, but if it is not done expertly this can simply induce further growth. Remember that established trees can be subject to preservation orders, issued by local authorities.
A leaflet on trees and subsidence is available from the Subsidence Claims Advisory Bureau.Reuse content