Tree roots may affect neighbouring land irrespective of whether the roots themselves encroach across the boundary of that land. Not only can tree roots directly damage underground structures but also, in altering the water content of the surrounding soil resulting in ground instability and subsidence, they may indirectly damage property on the surface.
In determining whether the presence of tree roots constitute a nuisance and potential grounds for a claim, the following test set out in the leading case of Delaware Mansions v Westminster City Council [2001] should be applied.
When is there a duty between neighbours with regard to trees?
A duty of care for the tree owner to do what is reasonable in the circumstances to prevent or minimise the risk of interference with or damage to the property of his neighbour, is established when the following is satisfied;
a) The tree owner knew of, or ought to have been aware of, the encroachment;
b) There was a reasonably foreseeable risk of damage to the property or enjoyment of it, as a result of the encroachment.
It should be noted that the nuisance “continues” from the previous owner of the property on which the tree is situated, to an incoming owner, provided that the above two-fold test is satisfied.
Did the tree roots cause the damage to the neighbouring property?
The onus is on the claimant to prove that the tree roots had materially contributed to the damage to the property however, it does not necessarily have to be the sole cause of the damage. There is an obligation upon the defendant, once aware of the potential problem, to do what is reasonable to address the issue; this is likely to go beyond regular preventative pruning standards and will be judged on the facts of the matter.
Was the harm reasonably foreseeable?
The tree owner must know, or ought to have known, of the presence of the roots and the risk they pose. In addition, the risk must be one which a reasonable person in the tree owner’s position would have regarded as a real risk (i.e. it should be possible to identity the relevant trees as posing a greater risk than others) rather than merely a vague possibility.
Were there any practicable steps that could have been taken to minimise or avoid the damage?
The timing of the risk management will be taken into account; tree owners should not be expected to remove all trees on suspicion that a small number of them may cause damage. Instead, a proportionate response is expected which may include pruning and pollarding trees that have been identified as potentially being an issue. Once again, the reasonableness of the steps that have been taken will be dependent upon the degree of potential damage, the state of the tree etc.
Was there a reasonable response to the damage?
If damage has occurred, the usual course of action would be to notify the tree owner in order to enable them to take remedial action. It was held in Delaware Mansions that the tree owner is entitled to a) notice of the nuisance, and b) a reasonable opportunity to abate the nuisance, before any liability for remedial expenditure arises.
Any claim for damages must also be reasonable. For instance, if the tree that is alleged to have caused the damage is several hundred metres away, it would be unreasonable for the claimant to seek damages for the cost of underpinning where repair for the damage, insertion of a root barrier and regular pruning would be sufficient.