Knot my problem? Surveyors and the curse of Japanese knotweed

We review the obligations on surveyors with regard to Japanese knotweed when carrying out residential property inspections.

Among the growing number of invasive non-native species found in the UK, Japanese knotweed reigns supreme. Introduced in the 19th century as an ornamental plant, it was not recognised as a severe threat to indigenous flora until the early 20th century. A perennial plant that spreads rapidly by its roots, knotweed can grow up to 10cm a day between April and October, and roots can be found as much as three metres deep and up to seven metres laterally. This can result in damage to drains, patios, boundary and retaining walls and outbuildings. In extreme cases, foundations and concrete walls have been damaged as well. It was only in 1981 that the plant was included in the Wildlife and Countryside Act, making it an offence to “plant or otherwise cause Japanese knotweed to grow in the wild”.

Impact on residential property purchasers

UK residential mortgage providers have been reluctant, and in some cases have outright refused to lend on knotweed-affected properties. Most lenders will require as a minimum a commitment to an effective long-term treatment plan, backed by insurance, as a condition of lending. Building insurance policies also generally do not cover damage and problems caused by knotweed, requiring a purchaser to seek out cover from a specialist provider before entering into a mortgage.


From a surveyor’s perspective, the pre-sale residential property inspection represents a challenge to identify the presence of knotweed, particularly when it is within the confines of a limited inspection for a mortgage valuation. If identified, mortgage lenders will expect the presence of knotweed to be noted on a mortgage valuation report. This puts an additional burden on surveyors to ensure that they are aware of the relevant risk factors and confident in their ability to identify the plant.

In 2012, RICS published an information paper, Japanese knotweed and residential property, providing detailed guidance and a standardised methodology for assessing the risks and quantifying the costs associated with knotweed on residential property when carrying out valuations and surveys. This is to be read in conjunction with the Red Book (Appendix 10) which sets out the standard for the external element of the residential mortgage valuation:

“although personal judgment has to be used, this inspection should include all of the property that is visible when standing at ground level within the boundaries of the site, and adjacent public/communal areas, and when standing at the various floor levels.”


“Where there are locational factors that may impact value they should be recorded and reported. Certain problems, such as…invasive vegetation…are particularly prevalent in certain districts. If appropriate, the valuer should make some reference to these defects, even if the subject property does not appear to be affected at the time of the inspection.”

The 2012 information paper identifies a number of useful factors to aid the surveyor in identifying whether knotweed may be a relevant issue for a particular inspection. Knotweed is typically found in the presence of:

  • Local water sources, such as culverts, ponds, canals and lakes
  • Public and private paths, cycle-paths, roads, railway or underground railway embankments, dual carriageways and motorways
  • Large open spaces, car parks and cleared sites
  • Commercial and industrial buildings, workshops, storage depots and similar

If a purchaser elects to commission a HomeBuyer’s Report, the 2012 paper provides further specific guidance:

“Although these are not specialist Japanese knotweed services, the inspection of the property and its grounds will be more comprehensive than with a mortgage valuation inspection and there will thus be a greater opportunity to identify any growth. In these cases, inspection along and over the boundaries is important especially where those features listed [above] are present.”

Legal implications

Rule 4 of the RICS Rules of Conduct requires members to carry out their professional work with due skill, care and diligence and with proper regard for the technical standards expected of them. This mirrors the duties imposed by law. RICS members will be expected to have maintained their professional competence by having knowledge of information papers within a reasonable time of their coming into effect.

A surveyor carrying out a property inspection will be judged according to the professional standards and knowledge at the time the inspection took place. RICS practice statements, guidance notes and similar documents are likely to inform that duty, but so will the type of inspection the surveyor has contracted to carry out. There are undoubtedly issues for the courts to address relating to the acceptable extent of an inspection in the time-limited context of a mortgage valuation report in particular, and also where the grounds of a property are extensive. However, while the primary focus must remain on the structure of the property, a surveyor ignores garden land at his peril.

Our content explained

Every piece of content we create is correct on the date it’s published but please don’t rely on it as legal advice. If you’d like to speak to us about your own legal requirements, please contact one of our expert lawyers.

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