Surveyors have updated their guidance on invasive species such as Japanese Knotweed when valuing property, but landowners and homeowners should continue to keep on top of their responsibilities in controlling this and other invasive, non-native plants.
One of the most common reasons for garden-related legal action is when Japanese knotweed has taken root. This highly invasive, aggressive and fast-growing plant can cause structural damage to building structures, with roots that can spread seven metres.
Even the smallest amount of root material is enough to allow new growth, meaning removal usually involves costly specialist waste disposal. Classified as hazardous waste, landowners can be fined up to £5,000 or sent to prison for two years if they allow contaminated soil or plant material from Japanese knotweed to spread in the wild.
Property values may be downgraded significantly where knotweed is present, and a landmark ruling in 2017 established that landowners are responsible if they do not prevent the plant from spreading from their land to adjoining properties. Here, a group of homeowners in South Wales took action against Network Rail after Japanese knotweed grew into their garden from adjoining railway sidings. In spite of there being no physical damage, the court ruled in their favour saying that the presence of Japanese knotweed was sufficient reason for compensation, as it had the potential to seriously affect the market value of a property. The judgement was later upheld by the Court of Appeal.
A further case in 2019 saw a £50,000 compensation pay-out being made after a surveyor failed to tell a buyer about knotweed at a £1.2 million flat.
And in one of the latest cases to reach the courts, the owners of a property in north west London are claiming £250,000 in compensation from their neighbours, saying that a failure to deal with knotweed has devalued their house, which would otherwise now be worth £1.67 million.
Typically, mortgage lenders have restricted their lending on properties that are affected and homeowners have found themselves having difficulty in selling, or finding the value of property significantly reduced.
But there may be a shift in attitude in future. For this year the Royal Institute of Chartered Surveyors (RICS) has issued new guidance for valuing property where knotweed is present. The RICS guidance for its surveyor members on how to assess the impact of any infestation suggests that previous parameters were overly strict and marks the end of the so-called “seven metre rule”. It also marks a shift in stance on managing any infestation, from permanent removal to achieve eradication towards management of the problem through herbicides.
Conveyancing expert Richard Joy commented: “While there may be a shift in future, until we see clear evidence of a greater acceptance of knotweed from surveyors and lenders, the message has to be to keep on top of any infestation, whether on your own property or in a neighbouring garden.
“If it’s on your land, while there is no legal requirement to remove Japanese knotweed unless it’s causing a nuisance to neighbours, inaction is likely to result in a bigger problem in future.
“Where you know it to be present on adjoining land, you should get a request on record for the neighbour or landowner to ensure it does not spread over the boundary. And once there is evidence of it crossing the boundary to your property, you may have grounds for a nuisance claim, and to ask for an eradication programme and guarantees from a specialist company, as well as seeking compensation. We have a Dispute Resolution team here who can help with this.”
He added: “Your home is usually your biggest asset, so it’s important to protect it - whether you’re planning on moving in the near future or not. Certainly, when a property is being sold, part of the conveyancing process includes a comprehensive questionnaire for the owner, which includes asking whether Japanese knotweed has ever been found on the property.”