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japanese knotweed devalues property


Japanese knotweed can decrease a property’s value by up to 20%, but the actual impact varies on a case-by-case basis. If only a small stand is present, the property value may only decrease by 5%. A larger infestation, however, could completely devalue a property! 


Why Does Japanese Knotweed Devalue Property?

Any infestation of Japanese knotweed makes a property less desirable for several reasons:

treatment costs
the potential for fines if the weed spreads
• property damage caused by the plant’s roots.

Under the Wildlife and Countryside Act of 1981, it is an offence to allow Japanese knotweed to spread from your property into the wild or to another property. This makes treatment an urgent priority.

The cost of treatment for even a small stand of Japanese knotweed could knock the asking price down quite seriously, because treating the plant is costly and can take several years. A buyer willing to purchase the house with knotweed present may want to set some money aside for professional Japanese knotweed removal, and so they might offer less for the property itself.

So, how do you know if your property value will be affected by Japanese knotweed?

Enter the chartered surveyor.

Selling a House With Japanese Knotweed

If you want to sell your property, it’s worth having a chartered surveyor fully examine it to determine how much the property is worth. There are various factors they look at to determine a property’s value, one of which is how much maintenance work needs doing.

In 2022, the Royal Institute of Chartered Surveyors (RICS) updated its Japanese knotweed guidance.

There are now four management categories, A – D, each with its own advice to mortgage lenders on whether they should offer a mortgage on a property with Japanese knotweed.

Category A is the most severe, where the knotweed is on-site and causing material damage. Lenders are advised not to lend a mortgage until a specialist report is obtained and a remedial plan is agreed. Category D is the most relaxed: the knotweed is within three metres of the site boundary but is not present on the site itself, so a mortgage can be offered in full except in exceptional circumstances.

If mortgage lenders can withhold some or all of the mortgage they might otherwise have given to a prospective buyer (known as mortgage retention), this can bring down the property value. The full value of the mortgage being unavailable to a prospective buyer means they may be forced to offer less than the desired asking price. If this happens with just one prospective buyer, it may not make a difference to the asking price. If mortgage retention forces multiple prospective buyers to make offers lower than the desired asking price, the seller may have to reduce the asking price in order to sell the property.

A chartered surveyor armed with the latest RICS guidance and the knowledge of treatment costs can advise a potential vendor on whether any Japanese knotweed on their property will affect its value.

If you are concerned about Japanese knotweed on your property, don’t hesitate to get in touch. We can survey your property to determine whether you have Japanese knotweed in your garden.

Book a Free Japanese Knotweed Survey

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