Japanese Knot Weed RICS Update 2022

If you haven't heard about Japanese Knotweed, it is a non-indigenous, fast-growing perennial plant with seasonal canes above ground and a substantive network of below-ground roots known as rhizomes. Dense clusters of Japanese knotweed canes known as "stands" can grow as much as 3 meters in 10 weeks, while it was previously believed that rhizomes could grow up to 20 meters.

Japanese Knotweed can grow through and exploit defects and weaknesses in concrete and cause various degrees of damage which, if not controlled, can lead to significant repair costs.

Japanese Knotweed started to gain bad press and had been cited as being able to cause structural damage to properties. To eradicate it quickly and effectively would mean significant excavation of the soil around the rhizome, and under the Environmental Protection Act 1990, Japanese Knotweed contaminated soil is designated as a controlled waste; therefore, only licensed organisations can remove it and have it disposed of at an appropriately licenced landfill site, increasing the costs of remediation.

A 2012 RICS information paper set out a strict framework on how its members should report on Japanese Knotweed and ultimately to the mortgage lenders. This was based on a 7m rule defining various measures regardless of the size and impact of the stands. As a result, several loans on properties affected by Japanese Knotweed were declined, resulting in property sales failing and increasing the plant's bad press.

Since its publication in 2012, research into Japanese Knotweed has influenced a review by the Government on the way surveyors report on its presence.

New research identified that rhizome growth was nearer to 3m than the 7m on which the 2012 paper was based. Further investigation determined that damage to a structure was only likely when Japanese Knotweed was immediately adjacent to susceptible structures. Further research identified an optimum method of controlling Japanese Knotweed with a correctly administered herbicide rather than deep excavation.

As a result of the extensive review, the RICS published a new Guidance Note setting out an approach to help RICS members determine the appropriate method for managing Japanese Knotweed. This is based on the surveyor's judgement rather than a defined framework. The new guidelines also aim to reduce the stigma associated with Japanese Knotweed.

To be continued……