Japanese knotweed: a knotty problem?

Favourite of Victorian horticulturalists, adventurous foragers and railway embankment engineers, Japanese knotweed has had an interesting history in Britain since its introduction in the 1840s.

In recent years it has become most famous for being the bane of many homeowners, because of the impact it can have on the valuation of a property. However, this could be changing with the release of new guidance from the Royal Institution of Chartered Surveyors (RICS) which came into force on 23 March 2022.

It is a decision for individual firms to take, but to date the approach of most mortgage lenders has largely been driven by 2012 RICS guidance which had strict views on how valuers and surveyors should approach Japanese knotweed.

This guidance stated that if knotweed was present and closer than seven metres to a building, it was a significant risk. Most lender policies reflected this thinking, and required a long-term, funded and insured treatment plan from suitably qualified experts to be in place before they would consider lending.

It has since become clear that this guidance is out of touch with the latest scientific research on both the threat knotweed poses and the way it can be treated. Essentially, although it can damage walls and outbuildings it does not seem to affect buildings as much as previously thought. And while it is a menace for homeowners looking to enjoy their gardens when present in large clumps, not least because of the rules about how invasive weeds and the soil they grow in can be disposed, a blanket approach to every small appearance is disproportionate.

The updated RICS guidance recommends that valuers take a more nuanced approach. It suggests that knotweed in a neighbouring property is unlikely to have an impact on value except in exceptional cases where it is present in large volumes.

When it is present on a property it asks valuers to consider any damage it is causing to structures, and if it is having a significant impact on the use of an amenity (like a garden). This sensible advice will help valuers assess more clearly the impact of knotweed on a property. We anticipate that lender policies will soon follow suit.

It is very good news for homeowners who will not have property sales put on hold because of small patches of this pernicious weed.   

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