Weed all about it: Japanese Knotweed and Professional Negligence

This article looks at the typical issues involved in professional negligence claims against surveyors in respect of property damage caused by Japanese Knotweed.

Japanese Knotweed, commonly known as Asian Knotweed, is recognisable by its pretty heart-shaped green leaves and red stems. Yet, Japanese Knotweed’s extraordinary powers of growth (the weed can grow 20cm in one day) and ability to penetrate concrete have caused havoc for property owners and the foundations of their homes. In some cases, mortgage lenders have even refused loans to anyone looking to purchase a property with the invasive weed on its land. Consequently, Japanese Knotweed has been the subject of a great number of professional negligence claims made against surveyors.

Surveyors’ Negligence

Typically, in cases involving Japanese Knotweed, a surveyor faces the accusation that their report omitted the existence (or understated the extent) of Japanese Knotweed on the purchased/neighbouring property and the likely cost of remedying the situation.

As this is a claim for professional negligence, any claimant would need to prove that the (1) surveyor owed a duty of care to identify the Knotweed; (2) this duty was breached; and (3) the claimant’s loss was caused by the surveyor’s breach of duty.

The primary question is whether the surveyor’s duty of care extended to identifying the existence of Japanese Knotweed in the claimant’s property. This issue was addressed in Davis v Marshalls (Plumbing and Building Development) Limited & Connells Surveying and Valuation Limited [2018]. The court held that the surveyor was not under a duty to identify Japanese Knotweed as the claimant had only instructed the surveyor to undertake a basic mortgage valuation. In other words, the scope of the surveyor’s duty will depend on the standard of survey that the claimant asked the surveyor to provide. Where, for example, a surveyor is asked to carry out a comprehensive structural building survey, the surveyor will likely have a duty to identify Japanese Knotweed on the property (and, most probably, on any neighbouring property too). On the other hand, as Davis v Marshalls demonstrated, a duty to identify Japanese Knotweed is less likely to exist with respect to a standard mortgage valuation.

Where a duty to identify Japanese Knotweed does exist, the surveyor will have been under a duty to carry out a “reasonable” investigation. What this means in practice will, of course, be a matter of contention. A surveyor would never be under a duty to excavate a property, but a reasonable investigation will be more involved where Japanese Knotweed is likely to be hidden (for example, during summer, when the weed’s rate-of-growth is significantly reduced). This very point was made in Ryb v Conway Chartered Surveyors [2019], where the court also held that the surveyor’s investigation was inadequate (and therefore a breach of his duty) because the claimant’s poor-sight meant he was particularly reliant on the surveyor for an accurate identification of Japanese Knotweed. The court’s reasoning would suggest that the scope of a surveyor’s duty to identify Japanese Knotweed may depend on the claimant’s particular situation.

Where a surveyor has a duty to identify Japanese Knotweed but fails to carry out an investigation (or a reasonable investigation), the surveyor will have breached their duty of care to the claimant. The court will then turn to the issue of causation.

A claim for professional negligence will fail if the claimant is unable to prove that a surveyor’s breach of care caused the claimant to suffer loss.

A key issue in such disputes has been whether Japanese Knotweed existed when the surveyor carried out their investigation. Plainly, if there was not any Japanese Knotweed on the purchaser’s property at the relevant time, the surveyor’s failure to carry out the required investigation would not have caused the claimant loss. Conversely, if there was Japanese Knotweed at the relevant time and the Japanese Knotweed subsequently damaged the claimant’s property, the surveyor’s negligent investigation is likely to have played a causative role in that loss. (Note that the “relevant time” is the surveyor’s investigation and not the completion of the survey; this is important because Japanese Knotweed’s extraordinary growth means that the weed may have be visible at the time of the survey but not during the earlier investigation.) In disputes centring on issues of causation, a Japanese Knotweed removal survey becomes an extremely important piece of evidence, as does any photographic evidence and notes taken by the surveyor at the time of their investigation.

Recoverable Loss

Where a claimant successfully establishes their claim, the final hurdle will be to persuade the court as to the amount of loss suffered. Typically, the loss claimed will be the diminution in value of the claimant’s property, which may include the fact that the property cannot be mortgaged, along with the costs of remedial work.

In response, a surveyor can make several arguments. First, effectively treating the problematic Japanese Knotweed will ordinarily rectify any diminution in a property’s value. Consequently, any loss attributable to Japanese Knotweed will be minimal with respect to diminution and largely consist in the cost of remedial work. Second, cases where mortgage lenders have refused to lend because of the existence of Japanese Knotweed are few and far between. Usually, a mortgage lender is willing to lend if an appropriate treatment is implemented. Third, a governmental report in 2019 found that Japanese Knotweed may be no more harmful to a property than other invasive plants. This report challenges the current RICS assessment framework for surveyors, issued in 2012. The existing RICS framework is currently being reviewed and an updated guidance is anticipated soon. A more evidence-based understanding of the harms attributable to Japanese Knotweed may well result in reduced negligence claims and/or claims of lower value.

Contact our Real Estate Dispute Resolution  team today

If you would like to discuss any issue relating to Japanese Knotweed affecting your property or want advice on bringing/defending a negligence claim, please do not hesitate to contact a member of the Real Estate Dispute Resolution Team on 01895 207835 or 01895 207295, or email us at propertydisputes@ibblaw.co.uk.