The mere mention of Japanese knotweed can send shivers down the spine of homeowners and buyers. This alien plant species can make or break a sale, affect your chances of getting a mortgage and have implications for your home improvement plans.

Sounds drastic, but is this pesky plant as serious a threat as it’s painted? Should you buy a house with Japanese knotweed – if, in every other respect, it’s your dream home? And what practical steps should you take if the worst happens and you find evidence of Japanese knotweed in your garden? We investigate …


What is Japanese knotweed?

Japanese Knotweed is a highly invasive plant. Introduced into the UK in the 19th century, it was deliberately planted by landscapers and railway companies looking to cover large areas, thanks to its speedy growth. Hardy enough to grow in most conditions, the weed has even been found in the challenging interior of Japanese volcanoes.

The plant tends to be dormant in winter, coming back with a vengeance in the spring when it can grow as much as 30cm in a week. Above ground, Japanese knotweed can reach the height of an average person, strangling other plants in its path.

But it is at its most threatening underground, where its extensive root systems invade foundations, drains and boundary walls, exploiting existing cracks and even growing through concrete.


What does Japanese knotweed look like?

Buying or selling a house with Japanese knotweed

Japanese knotweed has heart-shaped leaves and strong stems, which look a bit like bamboo. There are other types of knotweed, which aren’t as invasive or difficult to treat, and they are easily confused. If you suspect you have Japanese knotweed, get advice from an expert as soon as possible.


What can be done about Japanese knotweed?

Tackling Japanese knotweed is something you can’t attempt on your own. It can be treated, but you will need the services of a specialist.

Treatment is usually carried out in three ways:

  • Specialist chemicals are used to kill the plants and roots. With a serious case, this could involve repeated applications – in some cases over the years.
  • Removing plants and roots
  • Sealing it underground with a specialist membrane.

Removal costs could be anything from a few hundred pounds to more than £10,000.


Legal responsibilities for Japanese knotweed

Japanese knotweed is classed as ‘controlled waste’, meaning that it is a criminal offence to dispose of it in your garden or household bin. You will need to use a licensed waste carrier.

It’s not illegal to have Japanese knotweed present in your garden, but if it spreads to a neighbouring property you could be held responsible and face legal action.


What if I’m looking to sell my home with Japanese knotweed?

Your buyers’ building survey may pick up on the presence of knotweed, or state if your home is close to an area where the plant is present. However, if you know your home is affected by Japanese knotweed, you must declare it to any potential buyers. The cost of disposing of the weed, and putting right any damage, may need to be reflected in the selling price.

If you are found to have lied about the presence of Japanese Knotweed, your buyer could make a claim against you for damages.


TA6 property information form – Japanese knotweed

When you complete the TA6 form for your conveyancer or solicitor, you will be asked to confirm whether Japanese Knotweed is present on your property and whether you have a management plan in place. You should include a copy of the plan with the completed form.


Should I buy a house with Japanese knotweed?

It’s a good idea to have a Royal Institution of Chartered Surveyors (RICS) Building Survey – the most extensive, full structural survey – carried out if you suspect Japanese knotweed may be present in a home you’re looking to buy. Not all surveyors look for Japanese knotweed, so check that this is included. If there are signs of knotweed, you may need to commission a further specialist survey to assess the level of risk it poses.

The main issue for buyers is that you may struggle to get a mortgage for the property. Mortgage lenders will look for an assessment of how serious a case of Japanese knotweed the property has before deciding whether guarantees of work to eradicate the plant are needed or whether to refuse you a mortgage altogether. You may also be asked for a bigger deposit or to pay a higher rate of interest.

Even if you’re a cash buyer, you still need to be careful with knotweed, as its presence could affect the value of the property and your ability to sell it on in future. Don’t accept vague promises from the vendor that they will sort the problem out. Do your research and insist on a proper survey and an expert treatment plan with full insurance-backed guarantees and removal certificates.


How do lenders judge the severity or risk of Japanese knotweed?

According to RICS, there are five categories of risk depending on how close your home is to the knotweed, whether it is on the property or land close-by. The most serious infestations – category 4 or 5 – mean a mortgage offer may be declined.


Why does Japanese knotweed affect my mortgage chances?

Mortgage companies are lending you money against the security of the property you are buying, so they need to know that the home will retain its value long-term. Japanese knotweed can affect the property by invading cracks in walls and foundations, weakening the structure. It can also prevent you from building extensions or outbuildings on the premises. Even if the plant is dormant if you build on land where knotweed is present you risk reawakening it. For some lenders, a serious case of knotweed isn’t worth the risk.


Does Japanese knotweed affect house prices?

Because of the potentially high costs of treatment – and a general sense of panic around the issue, Japanese knotweed can affect property prices – impacting on your sale price by as much as 15%, although there are other factors to consider.

Finding knotweed on a property isn’t necessarily a deal-breaker – surveys suggest around a third of buyers would go ahead if they could negotiate a discount and know a treatment plan was in place. The important thing is understanding the implications of having Japanese knotweed and knowing what to look out for.


If you are a buyer or seller in the Wimbledon area, we can advise you on all aspects of your move – Japanese knotweed included. Contact us to find out more about our services and current properties.

About the author

Nicolas Holmes

Nick joined Robert Holmes to inject fresh ideas and help grow the New Homes department of Robert Holmes as well as helping to inject technology into the business and to grow its client base. Together with one of the Directors Nick is in charge of all Development opportunities that Robert Holmes deals with along with sales. Aged 40, he provides succession together with the two existing directors. Nick has always been focused on building client relationships and sales. He built up his own gallery in Chelsea, where he had a loyal following of customers and artists.

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