How Much can Japanese Knotweed Devalue a Property?

Japanese knotweed house price calculator

It’s a question we’re often asked, so we’ve teamed up with Expert Surveyors Ltd, the leading dedicated provider of RICS expert property valuation reports in the UK and created JK-VIM, a valuation impact model that gives indicative price reductions.

  • Explore how the value of a property can be reduced if it is affected by Japanese Knotweed
  • See the effect on value of a property if the knotweed is eliminated
  • Most will first require the knotweed is professionally treated
  • Most will also require the work to have an Insurance-backed Guarantee (IBG)
  • Our 2019 YouGov research revealed that half of all buyers would simply walk away from a property affected by knotweed
  • It also revealed that most others would look for significant price reductions
  • In legal cases, damages are awarded to cover the cost of treatment/removal
  • They also include diminution in value, the blight caused from the risk of knotweed re-growing
  • Read more about Japanese knotweed and the law here

JK-VIM gives an indicative valuation and includes revised valuations for the property if it has the benefit of a 10-year IBG following either herbicide treatment or physical removal. In most cases the cost of herbicide treatment or physical removal will be considerably less than the value added back onto the property by getting a professional firm to tackle the knotweed.

For high-value properties the extra cost of physical removal over herbicide treatment is often justified on purely economic grounds, when the residual diminution is considered. Removing the problem minimises the blight.

One last thing, actual market price, as opposed to a valuation, is the price that a willing buyer and a willing seller agree to – they are not necessarily the same!

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