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Japanese knotweed and its effect on property sales

by Iain Mason

Published on 14th June 2022

Horror stories around Japanese knotweed and its negative effect on the conveyancing process have abounded in the media.

The presence of this invasive plant species can mean people wanting to buy have difficulty in getting a mortgage. Banks and building societies are often deterred from lending against a property if there is even a hint of the presence of Japanese knotweed.

But a recent re-evaluation of this plant indicates these fears may have been a little overplayed, and – if lenders agree – then the prospects of getting a mortgage should increase.

What is Japanese knotweed?

Originally found growing inside Japanese volcanoes, Japanese knotweed is very hard to eradicate. Dormant during winter, its long, bamboo-like shoots erupt in the spring and grow extremely quickly. Even if it seems the plant has disappeared over a harsh winter, it will be lying dormant in the soil, ready to spring up, stronger than ever, when clement weather conditions prevail.

How does Japanese knotweed affect buildings?

When they sprout from the underground rhizomes (or roots), the shoots can damage foundations, brick walls, sewerage or drainage works. It is this characteristic that makes lenders reluctant to grant mortgages on properties which may be affected. It also makes homeowners reluctant to build extensions, conservatories or patios, because the plant may end up causing structural damage.

What has changed?

This is definitely not a case of a total makeover for Japanese knotweed. It is still problematic if it is too near your property, or gets into or under it. However, new research has been carried out into how ‘near’ is near.

Previously, if the plant was within seven metres of a property you wanted to buy, then lenders would be concerned. Indeed, the Royal Institution of Chartered Surveyors (RICS) has five categories, which broadly fit into how lenders view each knotweed problem, each rising in severity. Category 2 is ‘knotweed is within seven metres of your property but not within it’.

However, Defra has recently published its ‘International Approaches to Japanese knotweed in the Context of Property Sales’ report, advising the RICS of revised standards, which came into effect in March this year.

The main points of the guidance are:

  • Japanese knotweed rarely causes structural damage to substantial buildings such as dwellings and is not typically associated with major issues such as subsidence, heave or impact damage.
  • The seven-metre threshold has been reduced to a three-metre threshold (based on new evidence).
  • Reporting requirements to lenders will now be more nuanced.

This latter point relates to an update made by the Law Society in 2020, enabling a seller to indicate ‘not known’ if they were unsure whether knotweed existed or whether it had been previously managed on the property. The revised guidance was given because sellers, being unable to identify Japanese knotweed or understand the implications of its presence, were frequently ticking the ‘no’ box, leading to misrepresentation claims and, in some cases, litigation.

So what does this mean for homebuyers? It is hoped that this revised RICS guidance will increase the number of mortgage offers on affected properties that have a clear knotweed management plan in place.

While Japanese knotweed is, and will probably remain, an issue, this new guidance re-evaluates the impact of its presence on a property and will hopefully allow more transactions to take place.

If you are buying or selling a house and need conveyancing for the purchase or sale, please get in touch with the property law team at Optimum. We help people moving house in Swindon, Cheltenham, and the surrounding area.

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