British homeowners plagued by Japanese knotweed have seen £20 billion in total wiped off the price of their homes, according to new research.
Analysing data of its knotweed removal project over the past 20 years, Environet UK, the Japanese knotweed removal firm, estimates that between 4% and 5% of properties are affected by knotweed, directly through problems affecting neighbouring properties.
It calculates that between 850,000 and 900,000 homeowners in the UK will have seen their property values slashed by 10%, knocking £19.8 billion off property values.
Japanese knotweed was first introduced into the UK from Japan in the 1850s as an ornamental plant, but it is top of the Environment Agency’s list of the UK’s most invasive plant species, described as “indisputably the UK’s most aggressive, destructive and invasive plant”.
It can spread rapidly, blocking drains and ruining concrete drives and brick paving, and damaging conservatories and outbuildings.
Lenders are likely to reject mortgage applications for buyers of affected properties unless there is a professional knotweed management plan in place with an insurance-backed guarantee.
Sellers are also required by law to inform potential buyers when there is, or has been, a problem with knotweed.
Nic Seal, managing director of Environet, says: “Japanese knotweed is the problem that just keeps growing. For most people in the UK, their home is their biggest asset and often the ‘pot of gold’ they are relying on in retirement, but Japanese knotweed is having a serious impact on values by deterring buyers and making homes difficult to sell, even if the knotweed has been successfully treated.
“Several high-profile legal cases this year, whereby landowners were successfully sued for allowing Japanese knotweed to encroach on to neighbouring properties, have led to greater awareness among the general public of the damage Japanese knotweed can cause to homes and house prices.
“Those affected by knotweed should seek to resolve the issue as quickly as possible by appointing a professional removal firm and securing a 10-year insurance-backed guarantee for the work, which will can be passed on to a buyer and their mortgage lender. DIY attempts at treatment will usually only make things worse and can even hasten the spread of the plant.”
Mark Montaldo of Cobley’s Solicitors, which specialises in Japanese knotweed litigation, adds: "In legal cases, relating to diminution in value due to knotweed, we typically see claims for around 10% of the property’s value. This is due to the stigma attached to knotweed impacting on its future sale price.”