Study claims risk to homes from Japanese knotweed ‘overstated’

THE POTENTIAL risk posed to properties in the UK by Japanese knotweed is overstated, according to a study by Yorkshire academics.

Research concludes that automatically refusing mortgages on homes where the notoriously invasive weed is found is often out of proportion to the risk posed to property.

Ecologists from the University of Leeds and global infrastructure firm AECOM have completed extensive research to assess the potential for Japanese knotweed to cause structural damage.

The plant is a notorious nonnative species in the UK, and elsewhere in Europe and North America. Now recognised as one of the most problematic weeds, it is known to have a range of negative environmental impacts.

In the UK, Japanese knotweed is widely believed to pose a significant risk of damage to buildings that are within 23ft of the aboveground portions of the plant due to its underground shoots, known as rhizomes.

The stigma associated with the plant means that property values can be affected, even after action is taken to control it.

Research included assessing 68 residential properties where Japanese knotweed was found and data collected when it was removed from an additional 81 sites.

Dr Karen Bacon, a co-author of the study, from the University of Leeds’ School of Geography, said: “The negative impact of Japanese knotweed on such factors as biodiversity and flooding risks remains a cause for concern.

“But this plant poses less of a risk to buildings and other structures than many woody species, particularly trees.

“Japanese knotweed is capable of damaging built structures, but where this occurs, it is usually because an existing weakness or defect has been exacerbated.”

Professor Max Wade, technical director for ecology at AECOM, added: “We hope our research will inform discussions around the advice currently offered about Japanese knotweed.”