Japanese knotweed’s fearsome reputation among property owners and mortgage lenders could be reassessed following research from Leeds University and engineering firm AECOM.

Japanese knotweed is an invasive species, which has been linked to significant structural damage to properties.  It has been classified as ‘controlled waste’ under the Environmental Protection Act 1990 and must be disposed of securely if found. 

Some lenders will not offer mortgages on properties where Japanese knotweed has been found.  Otherwise a condition of a positive mortgage decision, is usually evidence of treatments that will eradicate the plant.

But now ecologists have identified no evidence that Japanese knotweed causes significant damage to buildings or that it is any more harmful than other species such as buddleia, trees and climbers.

Dr Karen Bacon, University of Leeds, School of Geography, said: “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.”

The research studied 68 residential properties where Japanese knotweed had been found and a further 81 sites where knotweed had been removed by excavation.

Property owners who discover Japanese knotweed on their land are not out of the woods yet,” said James Burgoyne, Director – Claims & Technical, Brunel Professions. “They could face legal action if it spreads to neighbouring land and they may find it difficult to sell their property or find its value significantly impaired.”

But these findings could be the start of a reassessment of the danger posed by Japanese knotweed.  They may be welcomed by property owners, and certainly by property professionals and their insurers given past issues involving the discovery of Japanese knotweed post purchase by a property buyer.”

Leeds University and engineering firm AECOM have published the findings on their websites.  Reports on the study have been published by Today’s Conveyancer and law firm Stephensons. Key facts about Japanese knotweed have been published here by the RHS.

Brunel provides a wide range of Professional Indemnity Insurance broking services to property professionals.  Click here to find out more, or call Mark Sommariva on 0203 475 3275.