Protecting Surveyors Bulletin 8: RICS 2022 Guidance on Japanese Knotweed – from chilling effect to lateral thinking

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With a view to limiting the effect of Japanese knotweed on the property market, the RICS has published new guidance which requires surveyors to adopt a structured approach in assessing the impact of knotweed. The RICS publication, “Japanese Knotweed and Residential Property” (effective 23 March 2022) sets out a new assessment criterion for surveyors to follow and comments that where knotweed is within property boundaries, the diminution of value is likely to be limited to the cost of remediation only. This is a noteworthy departure from the previous approach where all knotweed caused diminution in value; causing difficulties for buyers, sellers and lenders. Supported by new research, RICS notes that “substantial structures on sound foundations are unlikely to suffer structural damage due to Japanese knotweed.” Following the new guidance, surveyors need only observe and assess the above-ground elements of the plant, its location relative to the property and whether there are any material issues to the structure.


The predecessor RICS 2012 paper on knotweed specified four risk categories, using a distance of 7m between the plant and buildings or boundaries as the defining measurement (which was considered somewhat conservative). In 2018, published research concluded that knotweed poses “less of a risk of damage” to substantial buildings than many other trees or plants and there was general consensus that 3m would be a more appropriate distance measurement of spread in the soil, instead of the 7m distance adopted for the RICS 2012 risk assessment.

The House of Commons Science and Technology Committee’s 2019 report on knotweed acknowledged the importance of the RICS risk assessment framework in providing lenders with the confidence to lend against properties affected by Japanese knotweed but described the ‘7m rule’ as a ‘blunt instrument’ that did not reflect the latest scientific evidence (please see previous Law-Now for details). Echoing that approach, in 2020, DEFRA called for RICS to reassess the risk categories to provide clarity to lenders and promote a more helpful objective in the management of knotweed.

The new RICS guidance seeks to assist surveyors that encounter Japanese knotweed when assessing residential property. The publication provides a new framework for surveyors to categorise infestations of knotweed and sets out guidance for advising clients on remediation. By doing so, it provides much needed clarity for lenders and surveyors and manages the adjustment in the residential property market to the issues posed by Japanese knotweed.

RICS 2022 report

If Japanese knotweed is identified, from March 2022, surveyors will need to consider the new management category assessment decision tree (at section 4.5 of the RICS guidance), which defines the required actions from categorising the infestation to reporting. Further investigation can then be carried out by a recognised trade body, which will produce a report to determine whether a knotweed management plan should then be prepared. Other key changes in the new RICS guidance include:

  • Surveyors will only be expected to identify knotweed if it is “clearly visible” on site during a normal inspection.
  • Surveyors are not required to carry out a plant-by-plant check for knotweed.
  • The distance between the knotweed and a property’s habitable space or ancillary structures of significant value no longer affects the risk/management categories.
  • The new assessment considers the area of visible growth, rather than the previous consideration of the rhizome zone (modified subterranean plant stem that sends out roots and shoots from its node), which was the 7m distance around the visible extent of the plant.
  • The distance of off-site knotweed to the boundary of the property has been reduced from 7m to 3m.
  • The impact of the knotweed to amenity space (including patios, paths, driveways etc.) is considered.
  • The new property lending advice based on the severity of impact.

Practical considerations

The recent RICS guidance shows a more optimistic approach to the management of Japanese knotweed in an attempt to move away from the previous effect the plant had on the residential property market. Emphasis is now placed on control, not eradication. Although the potential damage that Japanese knotweed can cause is recognised, the guidance notes that structurally sound buildings are unlikely to be affected (save for knotweed within 3m of the property boundary).

The guidance provides a new structured approach for surveyors to follow in the identification and assessment of Japanese knotweed. Whilst the new decision tree provides clarity and structure, with an added degree of flexibility with reporting duties, there remains a significant degree of subjectivity which will require surveyors to exercise their professional opinion. It will remain to be seen whether the new approach will reduce the volume of claims against surveyors arising from surveyors’ reporting of Japanese knotweed and/or whether the quantum of such claims will be lower.

Further reading: RICS Guidance Note: Japanese Knotweed and Residential Property.