Japanese Knotweed

Even the smallest amount of root material is enough to allow new growth, meaning removal usually involves costly specialist waste disposal.  You do not legally have to remove it from your land unless it is causing a nuisance but, 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 northwest 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.