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Subsidence and Direct Damage
| Indirect Damage to Buildings |  |
Many buildings are located upon a shrinkable soil type (such as some clays); such soils expand and contract in response to their water content. The water content of shrinkable soils increases and decreases in relation to the natural seasonal changes of the British climate. In winter the shrinkable soil is wetter and increases in volume; in summer the reverse occurs. These variations are called Seasonal Fluctuations and are quite natural.
The Seasonal Fluctuations are modified by adjacent trees (and other vegetation). These are able to abstract large quantities of water from the surrounding soil, which can then potentially increase the shrinkage rate of the localised soil. In some situations where such shrinkage is close to a building, such localised shrinkage can cause a section of building foundation to drop further than a neighbouring unaffected section; the resulting deformation and movement can cause damage i.e. subsidence.
Buildings can also experience localised lifting of foundation sections through a process called heave. In these situations a localised area of shrinkable soil has increased in volume more than a neighbouring area; such localised expansion under a section of foundation can also cause building damage. Burst water pipes, drainage leaks or the removal of a large area of vegetation (such as a tree) can be a cause of heave.
It is estimated that during the period 1988 -1992, building subsidence related claims in Britain exceeded £1.6 billion. Understandably, insurance and mortgage companies have become concerned and many will now request an inspection and report of trees located close to buildings.
Sadly, due to the lack of knowledge of some building surveyors, many trees are removed as a primary cause of building subsidence when in fact they are not. According to analysis by the London Tree Officers Association, 70% of claims made against trees were unfounded (data source AMIUG).
Direct Damage to Buildings
Trees can cause direct damage to buildings and structures through direct contact with their roots, branches and trunk. Large established buildings such as houses are not normally affected; it is the smaller structures such as walls, patios, sheds and garages, which are most at risk. The damage would normally be caused by the annual increase in girth of the root, branch or stem - as it increases in diameter, it lifts or pushes the structure. The concrete foundations of most modern buildings are able to withstand such tree activity.
What You Should Do if You Notice Damage to Your Property
Bring it to the attention of the tree owner. In the case of Harrogate Borough Council, please send all correspondence to:
The Finance Section
Harrogate Borough Council
Department of Resources
Crescent Gardens
HARROGATE
HG1 2SG
Dependent upon type and extent of damage recorded and the response of the tree owner, make your insurance company aware of the damage (consider that the costs for repair of say a minor direct damage claim may not warrant the involvement of the insurance company).
Upon request of any technical evidence required to support any claims, ensure that this is provided as soon as is practical so that a speedy decision can be made on the claim itself.
Be prepared to accept that there may be a period of monitoring required for the damage area (up to 12 months), so as to determine the extent and type of movement observed in specific areas over different periods.