Important

Our impact calculator gives indicative valuations only and is not intended as a substitute for taking professional advice from an RICS Registered Valuer with the relevant experience in assessing the diminution in value caused by infestations of Japanese knotweed.

It is recommended that you obtain specific professional advice from an RICS Registered Valuer where you require a valuation upon which you can rely.

RICS Valuers using this tool should note this is an indicative tool only and is not a substitute for exercising their own professional judgement in all cases.

Limitations

Outputs may vary due to a number of factors outside of the scope of this tool. Specifically, but not exclusively, the tool is not suited where:

  • the property is located off mainland England & Wales
  • the property or land does not have residential land-use
  • the property is greater than 1 acre
  • the property is greater than less than £100,000 or greater than £2 million
  • neighbour disputes relating to knotweed encroachment are ongoing
  • value includes development or hope value

Please also note that the extent of knotweed is not easy to determine from visual inspection. Knotweed rhizome may be present underground but not be visible above-ground. Where the extent is estimated this does not necessarily represent site conditions.

Disclaimer

Our calculator has been developed by Environet UK Ltd, with assistance from Expert Surveyors Ltd, the leading dedicated provider of RICS expert property valuation reports in the UK.

No responsibility for loss occasioned by any person acting or refraining from action as a result of the use of this tool can be accepted by the authors/developers or Environet UK Ltd.

© Copyright Environet UK Ltd 2025

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Get peace of mind with an Instant Assessment.

KnotSure™ Property Risk Assessment

KnotSure™ is a professional report designed to assess the risk of Japanese knotweed affecting a property within 2.5 miles. It evaluates whether the invasive plant is likely to be present and provides insights into how it could impact the property’s value.

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With KnotSure™, you can confidently navigate the risks of Japanese knotweed and safeguard your property’s future.

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The Property

Our value impact calculator will assume that the property is impacted by up to 20m2 of Japanese knotweed within 3m of the boundary - it will then tell you the potential impact on the property based on - no management, a professional herbicide treatment programme and full removal having taken place.