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Ignore Japanese knotweed at your peril!

07 July 2017

Japanese knotweed is an invasive non-native species and is problematic because it can cause physical damage to land and buildings, particularly through spreading roots. During the summer months, it can grow up to 10 centimetres a day and roots can extend to a depth of three metres and up to seven metres laterally. The presence of knotweed can have a significant and detrimental effect on the marketability and insurability of property and may also adversely affect value.

In the recent County Court case of Williams v Network Rail Infrastructure Limited 2017, the claimants brought a claim in private nuisance against Network Rail. Private nuisance involves the unlawful interference with the use and enjoyment of a claimant’s land.

The facts

The claimants were adjoining freeholders of two bungalows in Maesteg, South Wales. The bungalows abutted a railway embankment owned by Network Rail. Japanese knotweed had been present on the embankment for at least 50 years.

The claimants argued their private nuisance claim in two ways:

  1. encroachment on the claimants’ land (i.e. Network Rail was liable as the owner of the embankment where Japanese knotweed was present for its encroachment onto the claimants’ land); and
  2. presence on Network Rail’s land (i.e. the presence of Japanese knotweed on Network Rail’s land was an interference with the quiet enjoyment and amenity value of the claimants’ land because it affected their ability to sell their properties at market value).

It is the second limb which is interesting. Before the decision in this case, the commonly held view was that a claimant could require the removal of Japanese knotweed which had spread on to its land, but could not require its removal from any adjoining land.

The evidence produced to the Court indicated that the roots of the Japanese knotweed had encroached onto the claimants’ properties up to the foundations and underneath the bungalows. Satisfactory evidence that physical damage had been caused to the properties as a result of the Japanese knotweed was not presented to the Court. However, expert evidence did confirm that even if the Japanese knotweed was treated, the saleable values of the claimants’ properties would be below market.

The decision of the Court

The Court held that:

  1.  the encroachment argument failed: the claimants had argued that in encroachment cases, the tort of private nuisance did not require proof of damage to the claimants’ property. This was not the case; in line with previous case law, physical damage to the property must be proven.
  2. the presence argument succeeded: the presence of Japanese knotweed on the defendant’s land had unlawfully interfered with the claimants’ quiet enjoyment and amenity value of their properties. The amenity value of the property includes the ability of a claimant to dispose of its property at market value. As the diminution in the value of the property arising from the Japanese knotweed had been proved in evidence, the claim succeeded.

On the facts, the Court was satisfied that the claimants had shown that the interference was reasonably foreseeable and that Network Rail had failed to do all that was reasonable in the circumstances to prevent the interference. The Court awarded the claimants damages for:

  • the cost of treatment programmes and insurance backed guarantees to eliminate the Japanese knotweed;
  • the residual diminution in value of their properties after the treatment had occurred; and
  • general damages for loss of amenity and interference with quiet enjoyment.

What is the significance of this decision?

The presence of Japanese knotweed on land may now be an actionable nuisance even before it causes physical damage to neighbouring land because of its effect on the amenity value of the neighbouring land, as a result of the diminution in its value. Careful management of Japanese knotweed (and indeed other invasive species) is therefore paramount.

While it may more often be found at residential properties, remember it can appear in any open land.

How can you protect yourself as a landowner?

As a current landowner:

Acquiring a property with open land:

  • Careful pre-contract inspection of the land;
  • Make sure your surveyor checks for Japanese knotweed or other invasive plants. If not qualified to advise, you may need to commission a separate report;
  • If you have any doubts, tell your lawyer of your possible concerns, so that additional due diligence can be carried out to clarify the position; and
  • Check the guidance via the above links.
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