Is Japanese Knotweed really a problem for home owners?

Japanese Knotweed is not the demon plant that can shatter concrete and undermine buildings that everyone believes, according to new research.

In fact, Japanese Knotweed is no worse for buildings than a tree or any other shrub growing nearby.

Scientists say the plant is relatively harmless and is a victim of bad media that has fuelled a fearful reputation that is largely undeserved.

The reputation of Japanese Knotweed is so bad, that many lenders refuse to offer mortgages to buyers or owners with the evil weed growing within seven metres of their homes and demand home owners draft a professional treatment strategy to cope with the fast-growing plant.

Estate agents even point out whether a property is suffering from Japanese Knotweed intrusion due to a fear that not doing so could land them in court for flouting consumer protection rules.

Now, research by a team from Leeds University and engineering firm Aecom has declared Japanese Knotweed to be almost harmless and found no evidence that the roots can grow through concrete.

The study examined more than 60 properties contaminated by Japanese Knotweed. The stigma associated with the weed means that property values are blighted even after action is taken to control the plant.

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Dr Mark Fennell, principal ecologist at Aecom, who led the study, said: “Our research sought to broaden existing knowledge about the risk to buildings of Japanese knotweed compared to other plants.

“We found nothing to suggest that Japanese knotweed causes significant damage to buildings – even when it is growing in close proximity – and certainly no more damage than other species that are not subject to such strict lending policies.”

“The seven-metre rule, although based on the best information previously available, was not a statistically robust tool for estimating how far the plant’s rhizomes are likely to reach underground.”

Despite this new research, within the last few weeks a senior appeal court judge has ruled that neighbours could sue each other if the “pernicious weed” spreads across boundaries.

This comes after two homeowners were successful in their claim against National Rail following encroachment of the plant onto their adjoining properties in South Wales, which grew behind their properties. This ruling could have further implications for homeowners in England and Wales going forward and raises questions over how this plant should be managed. You can read more about this case here.

Master of the Rolls Sir Terence Etherton states: “Japanese knotweed, and its roots and rhizomes, does not merely carry the risk of future physical damage to buildings, structures and installations on the land.

“Its presence imposes an immediate burden on landowners who face an increased difficulty in their ability to develop, and in the cost of developing, their land, should they wish to do so, because of the difficulties and expense of eradicating Japanese Knotweed from affected land.

“In this way, Japanese Knotweed can fairly be described as a natural hazard which affects landowners’ ability fully to use and enjoy their property and, in doing so, interferes with the land’s amenity value.”

Find out more information about Japanese Knotweed here.