Should I Buy A House With Japanese Knotweed?

By Paolo Martini on 16th June 2020 (updated: 17th February 2023) in Japanese Knotweed News | Knotweed Help

Japanese Knotweed continues to cause structural damage to homes across the country. Japanese knotweed causes damage to houses as it forcefully grows through cavities and cracks in asphalt concrete and walls. This causes Japanese Knotweed to devalue homes that possess it by up to 15%.

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Japanese knotweed has been estimated to affect up to 1.45 million homes throughout the UK [1], which amounts to approximately 5% of residential properties; with that in mind homebuyers have a distinct possibility of being presented with a home that is either currently affected by the invasive plant or has been in the past. Whether buyers are told about a property’s checkered past upfront or are left to make their own discovery after a survey has been taken, it’s worth understanding how Japanese knotweed affects homeownership and a property’s value.

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What is Japanese knotweed?

Japanese knotweed is an invasive plant that originates from Japan, China and Korea. After being discovered by European horticulturists in the 18th-century [2], the plant was imported into mainland Europe. The plant is known for being fast-growing and rhizomatous, meaning that it can grow from fragments of rhizomes that make up its root system. This rhizome dispersal has allowed it to spread throughout the UK and Europe.

What does Japanese knotweed do to a house?

In rare cases, Japanese knotweed has been known to cause structural damage to houses. The plant is more likely to damage outbuildings and ancillary features such as drains, greenhouses, pavement or patios.

The plant is known to spread very quickly between houses, it is difficult to eradicate and can also exploit existing weaknesses in buildings [3]. Buying a home with Japanese knotweed means taking on the responsibility of controlling it, and ensuring that it does not spread outside of your boundaries.

You’ll also want to ensure that the plant doesn’t get out of control to the point where it threatens your physical property and enjoyment of your home. The severity of the infestation will dictate how much time, effort and money you will need to rectify the situation, this is why it’s also crucial to understand how to get rid of Japanese knotweed effectively, as mistreatment can cause the knotweed to spread and cause further damage.

How much does Japanese knotweed devalue a house?

Japanese knotweed can devalue a house between 5-15% [4], however, in some more extreme cases, the plant has been known to almost completely devalue properties. The amount that a home is devalued by will depend on the severity of the infestation and its proximity to any buildings. For example, a small infestation that has yet to properly develop and is found at the back of a garden, over 7 metres from a building, may only devalue the property by 5%. Whereas a mature infestation less than 7 metres away from a building, could devalue the property much more.

Careful consideration of the severity of the infestation and its impact on the property’s value is needed when buying a property affected by Japanese knotweed. The seller may wish to downplay the severity of the infestation, in a bid to keep their selling price as high as possible. Getting an outside opinion, preferably from an expert Japanese knotweed surveyor, will give both parties a clear understanding of the realistic costs needed to rectify the infestation.

The extent to which properties are devalued may be decreased in the coming years. The RICS published new Guidance Notes on Japanese knotweed and residential property in 2022, with the aim of changing public perception of the plant’s ability to damage property. As this new, scientifically-backed information is disseminated to the general public, the impact that the plant has on housing prices should lessen.

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How are buyers notified about Japanese knotweed?

Buyers are sometimes notified about Japanese knotweed on a property by the estate agent or by the sellers themselves. In some cases, the property listing will explicitly mention that it’s affected by Japanese knotweed, in others a seller may go out of their way to avoid mentioning it. In a typical property conveyancing exchange, your solicitor should ask the seller to fill out a TA6 Property Information Form [5]. This covers the history of the property and gives the seller the opportunity to provide the unvarnished truth about the property they are selling.

Do estate agents have to declare Japanese knotweed to buyers?

Estate agents are required by law to honestly present properties to buyers [6], which includes being upfront about Japanese knotweed infestations affecting land. Should an estate agent choose to lie or omit knowledge of an infestation to a buyer, then they risk being reported to the National Association of Estate Agents. They may be banned from the profession if it can be proven that they have acted outside of the Consumer Protection from Unfair Trading Regulations. Despite the repercussions of doing so, this hasn’t stopped estate agents from downplaying or lying about the Japanese knotweed in order to make a sale.

Do home sellers have to declare Japanese knotweed to buyers?

Home sellers have to declare Japanese knotweed to buyers. Home sellers are legally obliged to fairly present their property to potential buyers, as they are bound by the same Consumer Protection from Unfair Trading Regulations that govern estate agents. The TA6 Property Information Form is the piece of paperwork that is most commonly used to inform buyers of any negative issues affecting the home, including Japanese knotweed. There is a specific question on the form that pertains to Japanese knotweed, which leaves very little room for sellers to manoeuvre. If your seller lies about Japanese knotweed then this can be used as evidence in a claim for misrepresentation against them in the future.

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Should Japanese knotweed always be mentioned on the TA6 Property Information Form?

The Japanese knotweed question is a standard part of the TA6 Property Information Form and can be found at 7.8. The question cannot be ignored and reads:

“Is the property affected by Japanese knotweed?”

The options to respond are either ‘Yes, No or Not Known’.

“If Yes, please state whether there is a Japanese knotweed management and treatment plan in place and supply a copy with any insurance cover linked to the plan.”

The options to respond to this sub-question are: “Yes, No, Not known, Enclosed and To follow”.

Will a surveyor check for Japanese knotweed?

A property surveyor might not always check for Japanese knotweed. Although chartered surveyors are trained to identify the plant, they will not necessarily go out of their way to look for it, especially if you have only commissioned a basic Condition Report, as opposed to a more thorough HomeBuyer Survey [7]. There have been cases where surveyors have missed Japanese knotweed when undertaking a Level 3 Survey, in these cases, the surveyor has been found negligent for missing the plant and not informing the buyer.

How much does subsidence from Japanese knotweed devalue a house?

Subsidence as a result of a serious Japanese knotweed infestation could devalue a house by 20% [8], and up to 80% in the worst-case scenarios. Subsidence is treated with heavy caution by mortgage lenders, who will often not lend at all if a property has been affected by it. In rare cases where Japanese knotweed has infested and compromised the land beneath a property, homes have seen drops in value from over £300,000 to just £50,000 [9]. Homes badly affected by subsidence are often only fit for cash buyers who are willing to take on the risk themselves but will therefore do so at a lower price.

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Can I get a mortgage with Japanese knotweed?

Getting a mortgage on a property with Japanese knotweed is not straight forward, and in some cases impossible. Banks and building societies are well aware of how Japanese knotweed affects property value. Although their stances on the matter vary, many lenders will flat-out refuse to deal with properties that have an ongoing Japanese knotweed infestation. In historic cases, some organisations will lend if it can be proven that the plant has been taken care of.

Paule Raine BSc FRICS MEWI from Expert Surveyors Limited said:

“In nearly all cases where a property has a knotweed infestation, a mortgage will only be available if you put in place a professional Knotweed Management Plan provided by an approved contractor – i.e. a contractor who is a member of the Property Care Association and who can provide a 10-year insurance-backed guarantee on completion of the treatment.”

Related: Getting A Mortgage With Japanese Knotweed

Does house insurance cover Japanese knotweed?

You can still get home insurance if you buy a home with Japanese knotweed, however, these will not cover the cost of removal or eradication of the plant [10]. Although it’s possible to buy Japanese knotweed-specific insurance for your home, you will not be able to do this if you are already aware that the plant is present on the property. The presence of the knotweed should not, however, affect your premiums.

Related: How Japanese Knotweed Affects House Insurance: Are You Covered?

How do I check if there is Japanese knotweed in the area?

Check if there is Japanese knotweed in a particular area by looking at a Japanese knotweed UK Map, this will give you an idea of how badly the chosen area has been infested with the plant. Bear in mind that these maps have been constructed with the help of volunteer data. Just because an area appears free of Japanese knotweed does not mean that it’s necessarily the case. The best way to make sure is to properly look for whilst visiting properties and pay close attention to public footpaths and nearby waterways in the surrounding area.

Can I kill Japanese knotweed myself after buying the house?

Killing the Japanese knotweed after buying the house is an option that you could take, however you must factor in the costs of doing so and also consider that the property will always be stuck with this stigma, regardless of if you fully eradicate it or not. By taking this approach you run the risk of making a purchase that is not in your best interests, which could also lead to mortgage lenders simply refusing to lend you the money needed to complete the transaction.

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Should you buy a house that used to have Japanese knotweed?

Buying a house that used to have Japanese knotweed should not be discouraged altogether. Due to the widespread nature of this plant, millions of homes of all varieties have now been tarred with the same brush. In the case where you have found a home that was once affected by the plant, you should demand to see documents that prove that proper treatment has taken place before you think about making an offer.

The property seller should have admitted that the plant used to affect the property on the TA6 Property Information Form and should also attach evidence that transferable, insurance-backed treatment has taken place. Japanese knotweed can be extremely resilient, especially to DIY attempts of removal, which can lead to it lying dormant underground, seemingly dead to the world. Insurance-backed treatment certificates give you the confidence to make the purchase, knowing that if the plant does return, then a company will be legally bound to finish the eradication [11].

Should I buy a house which has Japanese knotweed on neighbouring land?

Buying a house that is threatened by Japanese knotweed on neighbouring land could lead to problems further down the line, due to the legal implications of having Japanese knotweed on your land. Legally speaking, neighbours are under no obligation to eradicate the Japanese knotweed on their own land, they are only breaking the law when they allow it to spread onto neighbouring land [12].

Choosing to buy a home that is next door to a particularly aggressive Japanese knotweed infestation could lead to the plant spreading to your own land. Whilst you could then claim for the costs of removal from your neighbour, this process could take some time and in the meantime, your property would then be classed as being affected by Japanese knotweed.

Related: Japanese Knotweed Growing In Neighbour’s Garden: Legal Implications

Will I be able to sell a property affected by Japanese knotweed?

You will legally be able to sell your property at a later date, but you will need to have proof that the infestation has been treated by a PCA-accredited firm in order for any future buyer to have confidence in starting the purchase process. Even if it has been years since the treatment took place, you would still have to be upfront about Japanese knotweed affecting the property in the past.

Related: Guide To Selling A Property With Japanese Knotweed

Can you negotiate a lower house price after discovering Japanese knotweed?

If a survey reveals Japanese knotweed on a home that you are planning on buying then you should be able to negotiate a lower price as a result. Depending on the circumstances, it may be in your interest to suggest that a Japanese knotweed survey is undertaken by professionals so that you can acquire an estimate for the cost of removal. Most mortgage lenders won’t lend on homes affected by Japanese knotweed, or at the very least will require that a treatment plan is in place. Take this into account when negotiating a lower price on your prospective home.

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Is it worth buying a house with Japanese knotweed?

You may find that, despite the drawbacks involved, buying a house with Japanese knotweed is still a viable option. For example, if you are not planning on selling the house in the future, then you can live comfortably knowing that the Japanese knotweed infestation won’t halt the selling process down the line. In some cases, you might even find that the reduction in the value of a home affected by Japanese knotweed makes it more affordable for you. Each property should be taken on its own merits and you should aim to find out as much about the Japanese knotweed infestation before making any decisions.

Should I avoid any property with Japanese knotweed?

A property with Japanese knotweed shouldn’t necessarily be avoided altogether. If you are seriously considering buying a property affected by the plant, then you should make sure to contact your lender first to see what their position is. Don’t wait for the seller’s solicitor to provide information, get a detailed survey of the affected land and insist that the seller initiates and pays for the treatment before any exchange takes place. Considering that most Japanese knotweed treatment plans take a few years to work, most mortgage lenders require proof that this has been paid for upfront.

If you’ve already bought a house with Japanese knotweed and are now wondering where you stand legally, then we may be able to help you. Get in touch with us for guidance by calling us direct on 0151 668 0551 or use the contact form to send us a message.


[1] Japanese knotweed is knocking £34bn off UK property values – Yahoo

[2] History of Japanese Knotweed in Europe – University of Leicester

[3] Japanese knotweed is no more of a threat to buildings than other plants – University of Leicester

[4] Buying or selling a property affected by Japanese knotweed? – On The Market

[5] TA6 Property Information Form Example – The Law Society

[6] The Consumer Protection from Unfair Trading Regulations 2008 –

[7] Japanese Knotweed and residential property (Information Paper) 2012 – RICS

[8] Can I Sell a House with Subsidence? –

[9] Japanese knotweed invasion causes Hertfordshire home price drop – BBC News

[10] How Japanese knotweed affects your home insurance – Money Super Market

[11] Insured Guarantees – Property Care Association

[12] Wildlife and Countryside Act 1981 –

Paolo martini cobleys solicitor
Paolo Martini

Paolo Martini is the lead solicitor for Knotweed Help and has over 30 years of experience in the field of Civil Litigation and is an expert on the legal issues faced by individuals dealing with Japanese knotweed. Now considered one of the country's leading litigators in Japanese knotweed law he works alongside the country’s top barristers and experts. His in-depth legal experience and connections to the Japanese knotweed removal industry make him uniquely suited for handling your case.