Japanese Knotweed has historically been known to negatively impact the valuation and marketability of those properties affected by it. The issues it can cause, such as a threat to the structural integrity of buildings were thought to be understood. In England & Wales this concern could impact a buyer's ability to mortgage property. But, is it really any more of a threat than other plants and trees?

Comprehensive professional knowledge of the plant has developed in recent years. Importantly, it is now understood that Japanese Knotweed:

  • poses less of a risk of causing damage to substantial buildings in comparison to many trees or woody shrubs.
  • rarely causes structural damage to substantial buildings such as dwellings. It may, however, cause damage to light weight structures, freestanding walls, hardstanding, drains and other ancillary features where it is left unmanaged.

This knowledge has created a shift in focus, away from the potential risk of buildings and more towards the loss of amenity caused by Japanese Knotweed which, in itself, may impact upon the valuation assigned to a property. This change is now reflected in the new guidance from the RICS on dealing with Japanese Knotweed in residential property.

The new guidance

Defining measurement

  • In assessing the potential risks of Japanese Knotweed, the defining measurement will now be 3 metres from the nearest visible knotweed (rather than 7 metres from a building or boundary per previous guidance).
  • When assessing risks posed by Japanese Knotweed on adjoining land, the defining measurement will again by 3 metres from the boundary of the property.

Management category assessment process

The guidance sets out four categories – A, B, C and D – of severity of the plant, aiming to provide a consistent approach by lenders across the market where certain circumstances are found on site.

Management and control, not eradication

  • Following a report by DEFRA, it is now recognised that methods used to physically remove Japanese Knotweed can be costly and cause significant disruption. Eradication methods should, therefore, be used sparingly; the default position should, instead, be management and control.

Mortgaging property

Individual lenders will always determine their own policy responses to the different levels of risk posed by Japanese Knotweed. The updated guidance should, however, be welcomed by borrowers and lenders alike, not only giving greater clarity on this knotty issue, but also looking in the round at all permissive plants and trees.