Japanese knotweed is knocking £34bn off UK property values

The invasive weed puts properties at risk of damage and can knock thousands of pounds off the value. Photo: Clive Gee/PA Images via Getty Images

Infestations of Japanese knotweed are wiping 10%, or £23,530, off the average UK property’s value, new analysis has found.

Over 5% of UK homes are affected by the fast-spreading weed. This equates to 1,450,000 properties impacted, with £34.12bn ($44.76bn) in total knocked off in value, according to the research by tradespeople comparison site HaMuch.com.

Areas with higher house prices stand to lose more from knotweed infestation with homeowners in London in danger of losing an average of £47,546. In the south-east property values could fall by £32,664, followed by the east of England (£29,128), and the south-west (£25,976).

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With the highest house prices in the country, homeowners in Kensington and Chelsea risk losing £119,162 on the price of their property if they find it has been infested with knotweed. Westminster and Camden see the next biggest price losses, facing a drop of £93,860 and £86,280 respectively, while South Bucks is the sees the greatest loss outside of London at £59,792.

The average cost of treating Japanese knotweed with herbicide is £2,500 to treat Japanese and the average homeowner would have to shell out over £5,000 to excavate it, according to Japanese knotweed removal specialists, Environet UK. Infestations can take as long as five years to treat fully, racking up costs of tens of thousands of pounds.

Ignoring the problem is not a good idea as it may become difficult to sell a house affected by knotweed and homeowners are also liable if the plant spreads to a neighbouring property.

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The invasive weed puts properties at risk of damage as it can grow through cracks in concrete, brickwork, patios, asphalt, cavity walls, gutters, and drains, eventually forcing walls to break apart.

Mortgage lenders now require people selling properties affected by knotweed to provide evidence of a professional treatment plan along with an insurance-backed guarantee for the work, before they will offer a loan. Sellers are also required by law to inform buyers if a property is or has been affected by Japanese knotweed, as a specific question is now included on the TA6 conveyancing form.

Tarquin Purdie, Founder and CEO of HaMuch.com, said: “Knotweed is a homeowner’s worst nightmare and there really is no DIY fix for this aggressive backyard vandal. It can take months on end to ensure it has been properly disposed of but can be more costly should you decide to turn a blind eye.

“The quicker you can get on top of the problem, the better, as a house with knotweed will not only drop in value but will also struggle to find a buyer.”

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The plant dies back to ground level during winter but begins to reappear around March. Experts at Environet UK advise tackling the problem as soon as possible