Insurance Post

Subsidence - A growing problem

Rising subsidence costs may be attributable to planting decisions made in the past, but will today's planting habits cause similar problems? Jane Bernstein looks at the evidence

As subsidence costs soar, trees remain one of the major culprits.

Many of the problems emerging now can be blamed on poor planting decisions made in the past, but there are also trends today that are storing up trouble for the future. The good news is that subsidence caused by trees is an issue that can be risk managed - but is the insurance industry being sufficiently proactive to take advantage of this and are homeowners and local authorities prepared to take advice on board?

Many of the subsidence problems in the UK today, and particularly in London, can be traced back to trees planted in the Victorian era. Ian Brett Pitt, technical manager at InFront Solutions, explains that the Victorians tended to plant large forest trees. "When they were planted, no one really took into account the size the tree would get to or the longevity of the house itself," he comments, adding: "To complicate matters further, the majority of Victorian houses have relatively shallow foundations compared to modern property."

Shallow foundations

Tony Boobier, director of building services at Capita Insurance Services, also emphasises the problems caused by shallow foundations, although he believes it is unfair to entirely blame the Victorians for the current subsidence problems. He explains: "Subsidence occurs due to the influence of trees on clay, and usually affects shallow foundations. Where the Victorians got it wrong was in building houses with shallow foundations, which are more vulnerable to movement. In older houses, this can be balanced out by the more robust nature of the superstructure, and the construction materials used, both of which are usually more accommodating to slight movement."

In addition, it is believed that the Victorians did not intend for the trees to reach today's troublesome proportions. As Richard Rollit, Crawford's implementation manager, national building services, points out: "Trees planted in that era were generally well maintained up until the 1960s, but as funding has gradually been reduced, trees have started to grow."

Most agree that we are far better informed today about which trees to plant and where. However, there are some worrying trends that could well prove costly in the future. Gary Strong, UK subsidence director at GAB Robins, is concerned that developers "aren't all that interested in potential subsidence problems", warning that new housing estates where trees have been planted incorrectly will have problems in 20 or 30 years' time.

Ian Gammans, loss control manager at Zurich Municipal, comments: "It must be kept in mind that building areas have expanded in recent years and this can result in more buildings being exposed by existing trees." However, he adds: "I am not aware of any authority that does not have a policy of sorts to ensure that the correct trees are planted."

John Wickham, head of property claims at Norwich Union, points in particular to the problems caused by leylandi planted too close to a property. "There is a trend towards leylandi and they need to be planted a safe distance from the property (at least 10 metres or twice the height of the tree) with allowances made for potential growth."

Mr Boobier is confident there is an increasing awareness of the impact of trees on buildings among building professionals, explaining that for new buildings, codes of practice and design guides for foundations are reducing the likelihood of future damage. But he adds that there will still be a legacy of problems in houses already built with trees nearby.

"Equally of concern," says Mr Boobier, "should be the recognition that poor management and pruning of existing trees can also cause problems."

Michael Lawson, managing director of OCA, which is part of Cunningham Lindsey's subsidence alliance, is concerned about the ease with which anyone can buy and plant trees. "You can go into your local Woolworths and buy a tree. The trend today for planting in ignorance is extremely worrying." He also explains that with many of the species being planted today, we do not know how they will behave. "With global warming, people can now plant exotic trees in their gardens but we have no idea how they will behave on clay soil."

David Clifton, technical manager at Munters, is more optimistic. "I don't believe today's tree-planting trends are storing up trouble for the future.

People are becoming much more aware of the issues and problems regarding planting trees and subsidence. They understand that the impact of climate change means the drier the soil the more the roots will extend to seek out water."

Risk management

Certainly, a greater understanding of the problems is emerging but is this translating into effective risk management? Mr Brett Pitt comments: "We now have the technology to start predicting subsidence in advance.

We are in a position to tell insurers where the high-risk areas are going to be." He is quietly confident that insurers will become more proactive on the risk management side but warns that the industry may lack the resources to be sufficiently proactive. In particular, because subsidence surges are relatively infrequent, it is difficult to maintain the right staff for the job.

Some insurers are beginning to send information to their policyholders.

Norwich Union's Home Doctor guide, for example, gives homeowners advice regarding the planting of trees and approximate safe distances from the property. Mr Wickham says: "Homeowners do need advice on this and the Association of British Insurers is undertaking research at Cambridge University regarding the appropriate methods of tree management. Local Authorities should have the required knowledge."

According to Mr Clifton, local councils provide "excellent advice" for householders that are planting trees, taking into account whether they could put a property at risk of subsidence. But it is questionable how far homeowners are willing to take risk management advice. Mr Lawson does not believe that warning homeowners about the extent trees can grow will help the situation. "If you put a label on a tree saying this tree grows too fast for a small garden, then it will actually encourage people to buy it - what people want is fast-growing large trees that will cover their neighbour's fence or obscure an eyesore."


Nigel Barham, part of Cunningham Lindsey's senior management team for project-managed subsidence, is more confident. He comments: "Most homeowners are keen to avoid damage occurring to their homes and will take notice of straightforward, well-promoted preventative advice."

Mr Barham adds: "When dealing with existing trees, particularly mature trees, protected trees or third-party trees, more expert advice can be required. On the drains front, while most homeowners can ensure the visible drainage systems are functioning properly, few would want to undertake purely precautionary underground service testing."

Robert Withers, managing director of, doubts it is feasible to expect policyholders to take on risk management advice. He says: "It assumes that most homeowners are some sort of expert with regard to their property. Most go to work to pay their mortgage and insurance and expect the policy they have put in place to react if they have a problem, whether that be fire, flood or subsidence."

Garry Stone, director, Building Risk Solutions, says policyholders have been fearful of approaching their insurers with a potential problem. "It is one thing reporting a claim, it is another telling your insurer that you think your property is at risk - and the impact on premiums or not being able to get cover. Local Authorities have access to the necessary understanding but have limited resources to spread across many urban trees."

One of the most high-profile debates concerning trees and subsidence is the question of whether to get rid of a nuisance tree completely or try to manage it through pruning and maintenance. Most within the insurance industry are now convinced of the view that in most cases felling a problem tree is the only effective way to ensure the problem disappears. Mr Brett Pitt says claims that were handled in 1995, where trees were not cut down completely, are now coming back to haunt insurers with further associated claims.

Mr Withers explains: "The trouble with reducing a tree by pruning is that it becomes a regular maintenance item, which after a couple of years tends to get forgotten. Thereafter, the problem can come back and start a fresh insurance claim all over again."

The 'safest' option is to remove the trees, says Mr Boobier. "However, we have an obligation for the future and cannot afford to have a scorched earth policy. We have to leave some trees for future generations but we can be cleverer in what we do. Some forward-thinking initiatives undertake to restore the balance by replanting new trees in public spaces, which goes some small way to compensating for the environmental effect of tree removal."

Informed approach

Mr Lawson comments that insurers are too often made to feel guilty for having to cut trees down. He points out that trees are felled for many reasons other than subsidence. For example, to make way for highway developments, hospitals, railways and airport runways. He says: "If an insurer fells a tree because it is causing a problem then there is huge guilt surrounding that action."

The good news, according to Mr Lawson, is that insurers are becoming much better informed. "I think in terms of getting the message across, the past five years have been a revelation." He singles Norwich Union out for praise but adds that others are investing resources in investigating the problem and approaching it in an informed and responsible manner. "Insurers have grown up," he says.


To minimise problems, Zurich Municipal recommends that regular risk assessment and management measures are in place, which include:

- Check that trees are placed at a safe distance apart and away from buildings.

- Check that the appropriate type of trees are planted for the local environment (some require more water than others, for example, willows, oaks and cedars).

- Carry out regular pruning and thinning (care should be taken as chopping a tree back can stimulate a tree into new growth, encouraging it to consume more water than before).

- Undertake root pruning and install root barriers to limit growth.

- Carry out pollarding (where all the growth is removed back to the bole or trunk of the tree).

- As a last resort assess if problem trees should be removed.

- Regularly monitor and review all sites.

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