It is becoming widely publicised that Japanese Knotweed has the potential for catastrophic destruction, but is it really as bad as it seems?

Well, the answer to that is….. thorny. Physical destruction may be a bit of a myth, whilst Japanese Knotweed cannot break through concrete according to Environet UK Ltd it can certainly grow through existing cracks, gaps or joins in property pavements, pipes, walls, foundations, fences, out-buildings and conservatories.

However, the main impact on a property caused by this invasive weed is the stigma surrounding it. The mere presence of Japanese Knotweed can significantly affect the value, marketability and insurability of land and buildings; it can be incredibly costly and particularly difficult to eradicate; and, it seems, it can now give rise to an actionable nuisance.

The landmark Court of Appeal case of Williams v Network Rail Infrastructure Limited 2018 clarified a number of issues that were left uncertain at first instance.

It was ruled that physical damage, e.g. damage to foundations, was not a necessary requirement as the mere presence of Knotweed rhizomes (roots) in the soil imposed an immediate burden/restriction on a landowner. Knotweed, the Court of Appeal said, was a classic example of interference with the amenity of land. It is a natural hazard, which if it encroaches on your land will restrict your use and enjoyment by limiting your ability to develop the property and by placing on you an immediate burden to take steps to eradicate it. The mere presence of Japanese Knotweed on adjoining land may not be enough to succeed in a claim for damages, in which case a preventative injunction requiring appropriate treatment can be sought.

Nevertheless, in cases where adjoining properties are affected by Japanese Knotweed, it is highly likely that the underground rhizomes may have encroached onto a neighbouring property if the visible Knotweed growth is within 4m to 7m of the boundary.  This is where expert evidence to determine if encroachment has taken place will be crucial.

Japanese Knotweed claims are heavily reliant on expert evidence and ultimately it will come down to whose evidence is preferred by the Judge. It is therefore extremely important to have on board a credible and CPR compliant expert report to support your case.

It is advisable that a report is obtained early in the claim to ensure that there is a cause of action and it is within limitation. Where there is a continuing nuisance, i.e. Knotweed remains on a potential Claimant’s property, then the Limitation clock will not have started ticking, but where the Knotweed has been treated/eradicated then Limitation will expire 6 years from the date the encroachment took place.

It is also likely that a valuation expert will be required to assess any diminution in value to properly assess the “stigma” damages that have been awarded in such claims. There will of course be a pre-treatment and post-treatment valuation which could have significant implications on the overall value of the claim.

A more recent unreported case of Ryb v Conways Chartered Surveyors (2019) found a RICS surveyor negligent in carrying out his Level 3 survey and inspection. This case is of particular interest in its approach to calculating the diminution in value figure as Judge HHJ Luba QC considered particular characteristics of the property as follows:

• desirability of the property;
• extent of the infestation and size relative to the size of the garden;
• likely use for the affected land;
• proximity to a built structure;
• and the risk of the plant spreading to neighbouring land.

It is important to note that the surveyor in this instance did not take any photographs and could not support his defence. The case relied heavily on expert evidence and whilst it was accepted that there could be a margin of error depending on the scope of the survey, the location and extent of the knotweed and the time of year, the main question was - Would a reasonably competent surveyor have noted it? This case is the first to have looked at the facts of an individual case and the property itself, rather than estimate a generic percentage diminution in value.

Other points to consider: What is the client seeking to achieve? Will damages for treatment be awarded if permission to access the Defendant’s land is required? Would a mandatory injunction be more suitable?

Questions, questions, questions but all very relevant as these can ultimately affect the level of damages being claimed.

It is important to ensure that all funding options have been considered as it is highly unlikely that a claim of this nature will be covered by a home insurance policy. Here at Box Legal we can now arrange After the Event Insurance for Japanese Knotweed claims so if you operate in this field, do get in touch to find out more about our ClaimSafe After the Event Insurance for Japanese Knotweed claims.