Robbins v London Borough of Bexley

In tree-root subsidence claims, liability is determined by the ordinary principles of negligence and nuisance. Where the possible causes are confined to identified vegetation, the court must select the most probable cause, or the least unlikely of the available causes. The presence or absence of roots beneath a property is not conclusive of causation.

Foreseeability depends on the defendant’s knowledge of the risk in the circumstances. A local authority aware that mature trees may cause subsidence within a defined distance should adopt reasonable preventive measures. On the evidence, regular crown reduction was an appropriate response before later research showed that severe pruning, rather than ordinary pruning, was required to materially reduce moisture extraction.

The claimant owned a house adjoining a park containing mature hybrid black poplars. Seasonal movement and cracking affected a rear extension, and the claimant claimed the cost of repair, underpinning and general damages.

The parties agreed that the damage resulted from moisture extraction by vegetation from clay subsoil. The central disputes were which trees caused the damage, whether the Council reasonably ought to have foreseen the risk, what preventive measures were required, and whether those measures would have avoided the loss. The claim had begun in the County Court and was transferred to the Technology and Construction Court during trial. The resumed trial was heard by Edwards-Stuart J.

1. Liability and causation. The claim succeeded. The Council was liable for the agreed damages and the court reserved costs and interest. The damage was caused principally by poplar T2, with a material contribution from T1. The sharply reduced movement in 2007 resulted from the severe pruning of T2, to a lesser extent T1, together with substantially higher rainfall.

2. Where the court must choose between a limited number of identified potential causes, it should select the most probable cause, namely the candidate that is least unlikely. The apparent presence or absence of roots in trial pits or boreholes does not, by itself, establish whether a particular tree materially caused the damage: [2011] EWHC 2847 (TCC), at paras 216–219.

3. The court adopted the NHBC approach for immature trees. Where a tree has reached more than 60% of its mature height, it may be treated as mature for assessing its likely zone of influence. Below that threshold, the factor of 1.25 is applied to the actual height. This supported the conclusion that the other suggested trees were unlikely to have caused the relevant damage.

4. The Council had been on notice by early 1998 that the Danson Park poplars could extend roots to approximately 35 metres and cause subsidence beneath shallow foundations. It should therefore have implemented a structured programme of crown reduction, with pruning at three- or four-year intervals. It was not liable merely because it failed to fell the trees; regular pruning was an objectively reasonable response on the knowledge then available.

5. The Hortlink evidence showed that ordinary pruning does not reliably reduce moisture extraction. Severe crown reduction of approximately 70–90% of crown volume may reduce soil drying, but the effect may last no more than two seasons. The Council negligently failed to ensure that crown reduction ordered in 2004 and 2005 was carried out promptly. Had it been performed before the summer of 2006, the significant further damage would probably have been avoided.

6. Where a defendant is already shown to have breached its duty and the injury is of a kind likely to result from that breach, the defendant may bear the evidential burden of showing that the damage would probably have occurred in any event: [2012] EWCA Civ 349, at para 90. The Council adduced no evidence sufficient to establish that result.

7. The Court of Appeal’s decision in Berent v Family Mosaic Housing and the London Borough of Islington confirmed that tree-root cases are governed by the general law of negligence and nuisance, without special legal principles: [2012] EWCA Civ 961, paras 19–24. The court’s conclusions were consistent with that approach.

The claim was commenced in the County Court and was transferred during the trial to the Technology and Construction Court. The judgment does not state any appeal from the present decision.