This article is the first of two and is a general introduction to tree related subsidence and discusses mitigation. The second article looks at the recovery of the insurer’s outlay.
What is subsidence?
What is subsidence you may ask, especially those that don’t live in the South East of England – this is because it predominantly affects properties in the south of England, particularly London and the Home Counties.
Why is that? It is because the underlying geology in those areas is predominantly London or Oxford clays. Clay soils are prone to shrinking and swelling due to moisture content. More sedimentary rocks, such as Sandstone, don’t have this characteristic and don’t shrink and swell. It is the downward movement of the clay soils where there is a moisture deficit that allows the property to sink and causes cracking in the walls etc.
This is why those living in properties founded on clay soils are most at risk and why the damage is usually first noticed in the summer months or into autumn. During the growing season, trees take moisture from the soils and if they are in close enough proximity to property that can cause the property to sustain damage as the foundations move downward. Claims are then presented to insurers.
Insurers appoint loss adjusters to investigate the cause of the damage and where subsidence is suspected various investigations are carried out to determine the cause. These include:
- Site investigations – boreholes are excavated to assess foundation depth, soil consistency, identify roots and whether the soils are desiccated (moisture deficiency).
- Engineering evidence – an engineer will comment on whether the damage is caused by foundation movement. An indication of this is the nature of the cracking (tapered).
- Arborist evidence – a tree expert will review the site investigations and location of any trees and comment on whether the trees are having an influence on the soils below the foundations and are causative of the damage.
- Monitoring – property will be monitored by placing studs at strategic locations to see whether the property moves up and down over a period of time. You will really want to be looking at monitoring over at least one full season, but more can provide stronger evidence. You would be looking for downward movement in the summer months and upward in the winter months (cyclical movement). This is cyclical and is only caused by the influence of vegetation. Continuing downward movement may be an indication of drains being the cause rather than vegetation.
All the evidence should then be assessed together and if this points to the cause of the damage being tree root subsidence it will be necessary to consider how to stop and prevent further damage occurring (Mitigation) and whether insurer’s cost of repairing the current damage can be recovered from a third party tree owner (Recovery).
Mitigation
To achieve mitigation, it is necessary to engage with the third party tree owner to see if they will be willing to remove the tree that is believed to have caused the damage, if that is what the expert arborist recommends. They may sometimes recommend that the tree is reduced and maintained but usually they recommend that the tree is removed.
Third party tree owners can be domestic or commercial neighbours or local authorities and whether a tree will be removed and mitigation achieved will depend on who owns the offending tree. Local authorities are very reluctant to remove trees and before they do they have to follow a local consultation process where there are likely to be objections from members of the public. They will require strong causation evidence. Domestic and commercial third parties are more likely to remove their tree, even with fairly limited evidence, maybe just an arborist report. They need to be careful though and consideration should always be given to whether a tree is protected by a Tree Preservation Order (TPO) or by being in a conservation area – the arborist should advise on this in their report. It is a criminal offence to maintain or remove a tree with a TPO without a formal application to the local authority for permission. Stiff penalties apply for not complying and insurers should avoid encouraging a third party to remove a tree that is protected. The arborist will advise whether a TPO is in place or not.
Mitigation may or may not be achieved and where it isn’t, it is crucial that the tree owner is placed on notice that if there is further movement causing further damage a claim will be made to recover those further repair costs. Achieving mitigation, that is, tree removal is important because not only does it mean that further damage can’t be caused (the cause has been removed), it negates the need for more drastic engineering solutions such as installing a root barrier or underpinning the property to prevent further damage. Engineering solutions are very expensive and much more damaging to the environment than the environmental benefit of the tree remaining. To achieve mitigation will save insurers tens of thousands of pounds and potentially in excess of £100,000 if they have to underpin a property.
When seeking mitigation tree owners will often cite the environmental benefit of keeping the tree and it is good practice to advise them that this would be negated if an engineering scheme such as underpinning is required.
Loss adjusters will usually agree to plant another tree elsewhere to replace the one that is removed and this and the environmental impact should be mentioned when seeking to obtain mitigation.
