Japanese Knotweed

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.

09 Aug 2022

Team name
Joanne Wood

Joanne Wood

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.

M&P Commentary

Joanne Wood, Head of Property at Mullis & Peake LLP, said:

“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 ascertain firstly whether knotweed is present and secondly to keep on top of any infestation, whether on your own property or in a neighbouring garden.

You should not treat knotweed yourself unless you have the appropriate skills and experience. There are several companies that specialise in treating knotweed.

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.

Your home is usually your biggest asset. When purchasing a property; it is incumbent on a buyer to have their surveyor/a specialist check the property for knotweed and on owning a property it is important to protect it – whether you’re planning on moving in the near future or not.”


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