Expert Insights

Expert Insights

Knot in my back yard: Japanese knotweed and damages

Network Rail’s most recent round of litigation with two homeowners in Wales has seen its attempt to avoid liability for Japanese knotweed fail again. However, the Court of Appeal’s reasons for upholding the neighbours’ claim differed from those in the county court and explored the types of damage that give rise to an actionable claim for private nuisance, confirming that Japanese knotweed is a classic example of an interference with the amenity value of land.

The root of the issue

The Japanese knotweed in Williams and another v Network Rail Infrastructure Ltd [2018] EWCA Civ 1514; [2018] PLSCS 120 had been present on Network Rail’s embankment for at least 50 years. Two neighbouring homeowners brought claims in private nuisance on the basis that the invasive plant had caused damage to their properties. They sought an injunction to require Network Rail to treat and remove the knotweed on its land, and damages under various heads of loss.

At first instance, the court rejected the claim for private nuisance based on encroachment. Although it was satisfied that the roots of the plant were likely to have grown below the foundations of the claimants’ properties, it found that no physical damage had been caused by the encroachment. It also concluded that the diminution in the value of the claimants’ properties did not constitute damage. It therefore concluded that the encroachment did not give rise to a claim in private nuisance.

However, the claimants succeeded in persuading the court that the weed had unlawfully interfered with the “quiet enjoyment” or “amenity value” of their properties. The court agreed that the amenity value of a property could include the ability to dispose of it at a proper value. The court accepted evidence that the “stigma” of the plant’s presence affects the ability to sell a property at its market value, even after treatment to remove the weed, the securing of mortgage funding being one difficulty.

Having satisfied itself that there had been a breach of duty by Network Rail and that this had caused a continuing nuisance and damage, the court held that the claimants should recover the costs of treating the invasive weed plus damages for the diminution in the residual value of their bungalows (ie the reduced value even after the plant is treated, to reflect the stigma attaching to the properties), as well as general damages. The court decided that it was inappropriate to grant a mandatory injunction to treat the knotweed, because it would be vague and uncertain.

Digging into the detail

Network Rail appealed against this judgment. The grounds included a challenge to the finding that the pure economic loss suffered by a homeowner when their property value reduces as a result of the presence of Japanese knotweed constitutes an actionable private nuisance on the basis that it interferes with the quiet enjoyment of property.

The Court of Appeal noted that it is well-established that physical damage is unnecessary to complete the cause of action for nuisance through interference with the amenity of a claimant’s land. For example, loss of amenity resulting from noise, smoke, smell or other emanations may not cause any damage to the market value of the land such as you would get with tangible physical damage. Despite this, damages may be awarded for loss of the land’s intangible amenity value. The court noted that the relevant point is the objective effect on the amenity value of the land itself. It concluded that a party need only show a sufficiently serious interference with amenity – according to the character of the locality and the objective standard of the average person – for there to be an actionable private nuisance.

Nonetheless, the Court of Appeal held that it had been incorrect for the first-instance court to find that the presence of knotweed on Network Rail’s land was an actionable nuisance simply because it reduced the market value of the claimants’ properties.

The court explained that the tort of nuisance is not designed to protect the value of property as an investment or financial asset and it does not extend to a claim for pure economic loss. Instead, its purpose is to protect a landowner in their use and enjoyment of the land.

Despite allowing this part of Network Rail’s appeal, the court disagreed with the first-instance decision to reject the claim for private nuisance based on encroachment, namely the spread of the knotweed rhizomes (underground plant stems) on to the claimants’ properties from Network Rail’s land. The court stated that the difficulties associated with Japanese knotweed meant that it could fairly be described as a “natural hazard” and burden that can affect an owner’s ability to use and enjoy his land fully.

The court noted the findings at first instance as to Network Rail’s actual and constructive knowledge of the presence of the knotweed and the potential risks arising to adjoining properties. It also accepted that Network Rail had failed reasonably to prevent the interference with the claimants’ enjoyment of their properties. The court therefore concluded that Network Rail should be liable for the interference with the amenity and utility of the claimants’ properties from the presence of the Japanese knotweed rhizomes and it declined to interfere with the awards of damages made at first instance.

A growing problem?

Williams is the latest case to examine the implications of Japanese knotweed and the court’s approach drew heavily on various sources of guidance, although not all of them are now current. The court noted that the Council of Mortgage Lenders’ policy states that the presence of Japanese knotweed might affect the valuation of a property. Valuers who inspect property for mortgage purposes are generally instructed to report to lenders where knotweed is present and action is usually required if the plant is found within 23ft of a structure.

In terms of legislation, there is the risk of criminal and civil liability. For example, it is an offence under the Wildlife and Countryside Act 1981 to plant or otherwise cause the species to grow in the wild. Failing to control the plant can lead to a community protection notice being served under the Anti-social Behaviour, Crime and Policing Act 2014. Japanese knotweed is also classed as controlled waste under the Environmental Protection Act 1990 and must therefore be disposed of safely at a licensed landfill site according to the Environmental Protection (Duty of Care) Regulations 1991.

Until fairly recently, anyone with Japanese knotweed was advised to consult the code of practice published by the Environment Agency (EA) in 2013. This document gave advice on removal of the plant but it was withdrawn in July 2016 (although it is still on the website) because “the Environment Agency no longer provides best practice guidance”. There is a general guidance note available from the EA on preventing harmful weeds, but this is nowhere near as detailed as the original code.

In addition, the RICS published the professional guidance Japanese Knotweed and Residential Property in 2012 (amended in 2015). This paper outlines the problems caused by the plant, including to drains, patios, paths, drives, boundary walls, outbuildings, conservatories and gardens. The note details effective treatment and states that “eradication requires steely determination”. The RICS website now states that the document is “no longer current” but can be referred to for information.

Interestingly, it seems that the RICS may have shown support for a recent research report by the University of Leeds and infrastructure services firm AECOM which suggests that Japanese knotweed is relatively harmless (see The Telegraph, 7 July 2018).

Although it has previously been suggested that the roots of the plant can crack concrete and damage foundations, the research found that knotweed cannot grow through concrete and there was no evidence to suggest that it causes significant damage to buildings, even when growing close by. The report did acknowledge that knotweed can worsen existing cracks in structures. However, it also found that the plant prefers to grow around obstacles rather than burrow through them.

In view of the findings of this recent report, the Council of Mortgage Lenders may now be encouraged to change its policy on Japanese knotweed. If so, it may be that the courts’ recent protection of homeowners affected by knotweed will only need to be short-lived.

This article was written by Emma Humphreys. For more information please contact Emma on +44 (0)20 7203 5326 or

This article was first published in the Estates Gazette.

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