Property journalism ~ The roots of mass destruction

The Observer, March 2006

Have you made any sneaky trips to the local garden centre or stashed those winter wellies yet? Yes, spring is here and our thoughts are turning once again to our long-neglected gardens, plots and allotments.

But beware. Among the colourful shoots and shrubs lurk some weapons of mass destruction - the seemingly innocent willows, poplars and apple trees we plant near our houses.

The danger lies deep in the soil. During dry spells, the trees' roots snake out around a house's foundations in search of water, in some cases forcing it to move and even collapse.

The dry winter is bringing matters to a crisis. The wet spring of 2005 was followed by a summer of intermittent rainfall and then the long dry winter which has made a lot of the UK's soil very dry ... particularly in the famous clay belt that leads from Yorkshire's Humber to the west of England's Severn Estuary,' says the Subsidence Claims Advisory Council (SCAC).

So dry, in fact, that the most widespread hosepipe ban for a decade starts in the South East next month.

During these arid spells, trees that grow too close to homes can soon remove water and shrink the soil, with movement in the foundations causing the houses to slip, crack or crumble. 'It's intrusive, horrible and very, very nasty watching a house suffering from movement and subsidence problems,' says a spokesman for Hiscox, the leading home insurance company.

'They can't just be solved overnight with a large cheque for they often involve months and years of monitoring and distress before an insurance claim can be made.'

The worst culprit is the weeping willow. This tree may be renowned for its beauty 'but it can bring tears to the eyes of homeowners due to its legendary thirst and all its other destructuctive properties,' says a spokesman for Esure.

The insurer has now contacted the UK's main garden centres warning them of the perils of planting willows near residential properties and urging them to withdraw them from sale immediately.

'A willow's roots are so strong that they can force up pavements or breach water pipes, and if there is one near your home it can easily suck the soil dry and cause your house to sink,' says Nikki Sellers, Esure's home insurance manager.

Most trees should be planted as far from a house as their fully-grown height - or more. Willows, however, are different. They must be at least 40 metres away, or four times the distance of the average apple, pear or plum tree or those attractive laburnums, rowans and birches.

But if you do have a willow overhanging your patio, don't chop it down for that too could have dire consequences - another type of soil movement called heave. 'When you remove a tree, the water balance of the soild changes, causing the ground to swell which pushes up any structures that are build on top of it, such as house,' says Sellers.

There is only one short answer to a garden tree that has outgrown its welcome and that is pruning. 'If you cut away the larger branches and the extra foliage, their roots won't snake out so much as they won't need the same amount of water. It will certainly help to prevent a potential disaster,' says the SCAC.

Willows are not the only trees of mass destruction, however. Other dangerous water guzzlers are poplars, elms, oaks, hourse chestnuts, planes and ashes.

'A mature deciduous tree can draw up to 50,000 litres of water a year from the surrounding soil... Inappropriate species planted near to buildings should be avoided - the right tree for the right place should be the balance we look for,' says an SCAC booklet, Trees, Subsidence and Your Home.

The SCAC booklet also has some helpful tips for spring gardeners. 'Among the trees that can be planted nearer to your home - but not too near - are magnolia, yew, holly, laurel, spruce and pine,' it says.

While Esure advises: 'All owners wanting to put in trees should read up on the subject via planting guides on the internet or booklets. Remember, trees are not the only hazard during droughts. You should also monitor your drains and gutters by regularly clearing away leaves and debris to prevent unnecessary build-ups of water.'

Research by Zurich Insurance shows that there were 37,000 subsidence claims costing the insurance industry just under Ł200m in 2004. 'It's impossible to say how many claims there will be this year as they take months to come through after all the monitoring and checking, but there has been a real blip and, if the dry period continues, homeowners' monthly insurance premiums will increase,' says Esure.

Detection is usually the best cure, says Hiscox. 'The only way to help stem or prevent a catastrophe is to watch out for any tell-tale diagonal cracks in your interior walls - not just the hairline ones caused by new plaster drying out too quickly. If you see a crack, don't ignore it but call in a surveyor immediately and report it to your home insurance company.'

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