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Knotty no more : a common sense approach to Knotweed

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By Polly McBride


Published 04 February 2022


RICS has just released its long awaited guidance for surveyors on Japanese knotweed. The document marks a significant change in direction in terms of how Japanese knotweed is perceived and how it should be managed, noting that the existing “zero tolerance” approach does not align with weed management generally, where the aim is regular maintenance rather than permanent eradication.

The guidance confirms that Japanese knotweed rarely causes structural damage and has moved away from an analysis by reference to the 7 metre rule, focusing instead on the impact on amenity space, which will be fact-specific and depend on a number of issues including the location of the knotweed and the size of the property.

The guidance clarifies that:

  • A surveyor is not required to carry out a plant-by-plant check for Japanese knotweed;
  • Potential difficulties in inspection including dense vegetation, boundaries that are difficult to see or access and the date of inspection (whether during growing or dead season) are “fully recognised”;
  • There are many reasons why a completely competent inspection might not identify the presence of Japanese knotweed, for example small areas of knotweed could be difficult to see, it could have been cut down or cleared or it could be dormant;
  • Only if the knotweed is “clearly visible” on site during a normal inspection, will a surveyor be expected to identify it.

RICS have also produced a flow-chart designed to assist surveyors with their assessment of Japanese knotweed which results in the recommendation of 4 “management categories". If the knotweed is on site and not causing any visible damage to a structure (which has been recognised as unlikely), then the principal question is whether it is likely to prevent use of, or restrict access to, amenity space. If it does, then category B action is advised, with a recommendation that advice be obtained by the client from a specialist company and, where surveying for a lender, a mortgage retention be established pending the outcome of such advice.

If there is considered to be no effect on amenity space then category C applies, meaning no action required, although a recommendation to obtain a specialist report to consider future management is advised.

In terms of what qualifies as interference with amenity space, the guidance clarifies that such space is regarded as open areas intended for recreation, leisure or convenience within the boundaries of the property; for example, lawns, patios, paths, driveways etc. Importantly, where Japanese knotweed is present but not affecting amenity space (for example in an unused flower bed or within the land of a large country estate), it is recognised that there may be no real impact on the value of the property and it should be treated by lenders in the same way that large trees and other plants are treated – ie accepted as a normal risk.

In conclusion, while RICS confirm that there is likely to be a diminution in value for category B knotweed, any effect on value for category C knotweed is likely to be modest and limited to the cost of remediation only. This is a significant departure from the previous approach for assessing diminution in value which was applied indiscriminately for all knotweed found on site.

In respect of assessing the financial impact on the value of a property, RICS helpfully summarise how this is undertaken. This does not depart from the current widely-accepted approach which has developed from the relevant authorities but is useful as a summary and may also assist in managing claimants’ expectations when considering bringing a claim against a surveyor for failing to spot Japanese knotweed.

A further aspect also emerges which should prove extremely helpful in defending some claims of this type, if properly communicated to the client at the outset.

Whilst arguably a statement of the obvious, the guidance notes that if Japanese knotweed “is clearly visible on site during the normal course of any inspection, it is reasonable to expect, all other things being equal, that it should be identified by the valuer or surveyor and reported to the client”. Further, that seeking to exclude all liability for failing to spot the obvious is unlikely to satisfy the requirements of the Consumer Rights Act 2015.

However, the guidance recognises that most RICS members are unlikely to have the necessary skill, knowledge and training to offer “the additional service of identifying and advising on Japanese knotweed as part of a pre-purchase survey”, and should therefore instead, if a client requires such advice, recommend that the client commissions specialist advice.

In our view, all valuers and surveyors should take care to manage expectations at the outset by clear communication and terms of engagement so as to limit, if not exclude altogether, liability to only those instances where the presence of Japanese knotweed is obvious and to ensure their clients are in no doubt that only specialist advice will offer certainty.