06 July 2018

Landowner liability for Japanese Knotweed

Landowners have a measured duty of care to ensure that Japanese Knotweed does not spread from their land, following the Court of Appeal decision in Williams v Network Rail Infrastructure Limited. Even in cases where no actual physical damage has been caused, the court decision opens up claims by neighbours for loss of amenity value due to the hazard created by the mere presence of the plant’s rhizomes under their property.

The judgment makes it clear that landowners must take reasonable steps to prevent or minimise the spread of Japanese Knotweed across the boundary. Whether a defendant has taken ‘reasonable’ measures is determined on a case by case basis but guidance can be found in the long line of nuisance cases where the interaction between neighbouring landowners is assessed on a ‘give and take’ basis.

Our experience from numerous environmental nuisance cases is that there is no 'one size fits all' test for reasonableness in nuisance, and landowners will need to be careful that their actions (or inactions) fall the right side of the line.

However, for many landowners who have been following these proceedings, the Court of Appeal judgment may be welcomed for re-establishing well understood principles of nuisance, and rowing back from the rather more bullish decision at first instance.

In the Cardiff County Court decision, the mere presence of Japanese Knotweed on one’s land could lead to successful nuisance claims from neighbours whose property value was diminished by the proximity of the plant. That judgment was viewed as paving the way for a broader interpretation of the law of private nuisance than had previously been seen, and created a degree of anxiety in the industry.

Case analysis

The claimants owned bungalows next to land on which grew a large stand of Japanese Knotweed, a non-native invasive species known to cause significant damage to buildings when left unchecked. This land was owned by Network Rail, who had carried out sporadic herbicide treatment to the Japanese Knotweed but no comprehensive treatment plan ensuring the thorough removal and destruction of the plant.

The claimants argued that they had:

  1. an "Encroachment Claim" against Network Rail in so far as Japanese Knotweed roots (known as "rhizomes") had spread underneath their properties
  2. a "Quiet Enjoyment/Loss of Amenity Claim" on the basis that the presence of Japanese Knotweed on Network Rail's land was a serious interference with the quiet enjoyment or amenity value of their properties, such as to constitute an actionable nuisance.

The recorder did not agree with the “Encroachment Claim”, stating that while the presence of the rhizomes under the claimants' properties was established, a claim in nuisance for encroachment necessarily required some physical damage. In this case, neither side's experts had identified damage to the properties or any change in the soil structure.

However, the recorder found favour with the claimant’s “Quiet Enjoyment/ Loss of Amenity Claim”. He considered that the amenity value of a property could include the ability to dispose of that property at a proper value, and that the presence of untreated Japanese Knotweed on Network Rail’s adjoining land constituted:

  1. a stigma which diminished the property value (lenders usually require insurance-backed guarantees of effective treatment of the Japanese Knotweed and even then the value is diminished)
  2. a blight which caused the property owner to suffer "loss of enjoyment" from the uncertainty that the property may not be as valuable as it was thought to be.

This was akin to actionable damage, rounding off the requisite elements of a nuisance claim.

Having established that a cause of action had arisen under the “Quiet Enjoyment/ Loss of Amenity Claim”, the recorder went on to assess whether Network Rail had breached a duty of care and caused the diminution in value. He held that Network Rail had sufficient constructive knowledge of the presence and risks associated with Japanese Knotweed, and that it had not done all that was reasonable to prevent or minimise interference with the claimants’ use and enjoyment of their properties.

What did the Court of Appeal decide?

The Court of Appeal took a different view, considering that the recorder's decision in respect of the Quiet Enjoyment/ Amenity Claim "extend[ed] the tort of nuisance to a claim for pure economic loss" which would "not be an incremental development to the common law by way of analogy, but a radical reformulation of the purpose and scope of the tort". The judge was of the view that the purpose of the tort of nuisance was not to protect the value of a property as an investment or financial asset, but to protect the use and enjoyment of land "as such".

However, the judge also disagreed with the recorder’s view that a nuisance claim on the basis of encroachment necessarily required “actual” physical damage. He took the view that encroachment of Japanese Knotweed rhizomes imposed an immediate burden on any owner of land wishing to develop it, making this a "classic example of an interference with the amenity value of the land".

Japanese Knotweed was pernicious and carried with it the risk of future physical damage, and methods of eradication imposed difficulties and increased costs for landowners wishing to develop their land (Japanese Knotweed is classified as "controlled waste" and treatment methods require excavation of knotweed affected soils, installation of a root barrier membranes and other expensive measures).

Encroachment of rhizomes on the claimant’s land, in the context of constructive knowledge and failure to act reasonably by Network Rail, did constitute an actionable nuisance claim. The decision of the recorder to award damages to the claimants was upheld.

What does the decision mean for landowners?

While the Court of Appeal's decision steers away from an implication that the mere presence of Japanese Knotweed on one's land might give rise to private nuisance claims from neighbours, it nevertheless consolidates the view that landowners must take reasonable steps to prevent or minimise encroachment of Japanese Knotweed on adjoining land.

The development of private nuisance law (in particular in Leakey v National Trust for Places of Historic Interest or Natural Beauty [1980]) indicates that "doing nothing" to prevent a nuisance is not a viable option. Landowners need to consider what steps to take to address Japanese Knotweed on their land and decide whether active steps are required to prevent rhizomes extending under the boundary fence.

Key contact

Michael Barlow

Michael Barlow Partner

  • Head of Environment
  • Head of Water
  • Head of ESG

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