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Japanese Knotweed – What you need to know

Japanese Knotweed – What you need to know

Japanese Knotweed is a fast-growing invasive plant which can grow up between 10 - 20cm a day. Due to its rapid and aggressive growth, it has been known to cause damage to building structures and can exploit existing weaknesses in a property such as underground services, foundations, fences, out-buildings and conservatories.


The presence of Japanese Knotweed brings a number of potential liabilities for property owners, particularly structural risk to property. Identifying whether Japanese Knotweed has previously affected or currently affects a property is a difficult question for a Seller (as a non-expert) to answer and as a result 'Not Known' is an extremely common answer in conveyancing transactions.

If Japanese Knotweed were to be found on the property following completion it would (in most circumstances) become the responsibility of the Buyer. This may then require a treatment plan which, depending on the type of treatment and extent of the growth, could cost anywhere from £3,000.00 - £20,000.00 and take 3 - 5 years to complete.

Points to be aware of when selling a property/ replying 7.8 of the Property Information Form

As a Seller, if you are unsure whether Japanese Knotweed exists above or below ground or if it has previously been managed on the property, you should indicate your response as 'Not Known'.

If 'No' is chosen as an answer, this would indicate that the Seller is certain that no rhizome (root) is present in the ground of the property, or within 3 metres of the property boundary, even if there are no visible signs above ground. If this response is provided and evidence of Japanese Knotweed is then found, there may then be course of action against the Seller for the provision of misinformation.

Points to consider when buying a property/replies to question 7.8 of the Property Information Form

We would strongly recommend that a Buyer obtains a Homebuyers Survey prior to exchange and completion. In addition, the Buyer should also check whether the Survey terms and conditions include or exclude investigating the presence of Japanese Knotweed, to ensure that they are adequately protected in this regard.

Furthermore, where a Seller has answered 'Not Known' in respect of knowledge regarding Japanese Knotweed, we would then suggest that you consider whether a Japanese Knotweed Legal indemnity insurance Policy would be suitable, which would provide up to £20,000.00 cover for treatment costs and remedial work to the property (be it buildings or gardens) in the event that Japanese Knotweed is found on the property.

For individual advice and assistance please contact our Residential Property Team to find out how we can help.

This is not legal advice; it is intended to provide information of general interest about current legal issues.

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