Selling A House With Japanese Knotweed

Selling A House With Japanese Knotweed
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For many potential vendors, they may believe that selling a house with Japanese knotweed will make their home less appealing to a potential buyer – but that’s not always the case.

While many potential buyers will undoubtedly be put off from buying a home with knotweed, it is not – according to one survey, at least – necessarily a deal-breaker for most house buyers.

However, if you know that your property or a neighbour’s property has knotweed, you must:

  • Tell the property buyer that there is Japanese knotweed present (even if it is on a neighbouring property);
  • Do not pretend your property or a neighbour’s property doesn’t have the problem;
  • You will need to declare the fact on an official form.

This final point is crucial – you need to understand that you are under a legal obligation to tell the potential buyer about the issue.

If you don’t, you may be in a similar position with the seller, who was sued for £200,000 after failing to disclose the presence of Japanese knotweed.

Why is having Japanese knotweed such a problem?

Firstly, not only was Japanese knotweed a popular plant for Britain’s gardens, but it has also grown extensively around the country.

It proved to be popular because it survives very cold winters, but with the milder conditions in Britain’s winter months, the knotweed can grow quickly.

Indeed, in the summer, it can grow by up to 20 cm each day.

The roots can go down as far as three metres, and it’s these roots that bring a risk to the property’s foundations.

Just about everyone will have heard of the problems associated with Japanese knotweed since awareness of this plant has grown substantially in recent years.

This is the country’s most invasive plant, and it can cause extensive damage to property if it is left unchecked.

To give you an idea of how extensive the problem is, around 5% of homes in the UK are believed to be affected either indirectly or directly by Japanese knotweed.

In fact, Japanese knotweed management garners an estimated annual cost of £165,609,000 (Williams et al., 2010). Other indirect costs can also be traced to property devaluation and legal counsel.

As mentioned, you are under a legal obligation to tell a buyer that Japanese knotweed exists on your property, and it will be a criminal offence not to do so.

How to identify Japanese knotweed

Japanese Knotweed Flowers

If you suspect that your property or land has Japanese knotweed, and you want to sell your home, then you need to carry out an inspection.

Try not to disturb the weeds or risk spreading them further on your property or a neighbour’s property.

The best way to determine whether Japanese knotweed is present is to hire a professional to carry out a survey.

However, if you want to do a premilinary check yourself, here’s what you need to know…

Japanese knotweed will first show itself in spring when small shoots will appear that look similar to asparagus but are red or purple. The shoots will quickly turn into green stems that look similar to bamboo and grow very quickly, up to around 3m in height.

The leaves of Japanese knotweed are bright green and heart-shaped with a smooth, rounded edge, flattened base and pointed tip. As the leaves grow on alternate sides along the branches, you’ll notice a distinct ‘zig-zag’ growth of the branch.

Once the leaves are fully grown they will remain a vivid green colour until they die off later in the year. The leaves reach a maximum of 120mm in length. If the leaves are longer than this, you probably do not have Japanese knotweed.

By early summer, the Japanese knotweed plant is usually fully grown and will begin flowering by late summer.

Japanese knotweed flowers are creamy-white in colour and develop in small clusters. Each plant can have dozens of these clusters but the seeds are rarely viable in the UK.

According to a root system growth simulation in the UK by Smith et al. (2007), each cluster can develop a rhizome network of up to 200 square metres.

In autumn, the leaves will fall to the ground and the stems will become dark brown in colour. Japanese knotweed remains dormant over winter will be come back with a vengeance in Spring if left untreated.

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Japanese knotweed look-alikes

There are a number of Japanese knotweed look-alikes that often get people unnecessarily worried. One of the most common is bamboo, since the stems bear a resemblance to the stems of Japanese knotweed.

However, unlike Japanese knotweed, bamboo shoots are hard and cannot easily be snapped and the leaves are very slender and long.

Woody shrubs and trees such as lilac and dogweed can also sometimes be mistaken for Japanese knotweed. However, leaves often grow opposite each other on such plants and so you don’t get the distinctive zig-zagging of branches like you do with knotweed.

Houttunyia is another plant commonly mistaken as Japanese knotweed. However, these plants will only reach 30cm in height so can soon be discounted once they stop growing.

In addition, red bistort, lesser knotweed, Himalayan balsam, broadleaved dock, bindweed, Himalayan honeysuckle, and Russian vine can also be mistaken for knotweed if you are not familiar with how to identify Japanese knotweed.

How Japanese knotweed affects house selling

You might need to fix your Japanese knotweed problem before selling your home.

Having mentioned that not every potential homebuyer will be put off by the prospect of having to deal with Japanese knotweed, be prepared for them to ask for a reduction in the property’s price.

And the home buyer will not be looking for a saving of a few hundred pounds, or even a thousand pounds – one survey reveals that your property’s value could drop by up to 10%, and potentially by up to 15%.

And in rare cases of severe infestation, your home may be deemed worthless until the issue is fixed.

This means it’s probably cheaper to deal with the knotweed problem yourself rather than take a hit on the value of your home.

On the bright side, however, research from Environet, a firm that deals with knotweed, found that 32% of homebuyers say they would still go ahead with purchase a property that had knotweed.

However, that was only if they had enjoyed a suitable discount on the purchase price.

Other problems when trying to sell a home with knotweed, include:

  • Mortgage lenders may be reluctant to offer a loan;
  • You will have to reveal that Japanese knotweed is on the property using the TA6 property information form.

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Removing Japanese knotweed from a property

It’s highly likely that the survey report paid for by the buyer will highlight that Japanese knotweed is present on your property.

It’s also likely that the sale will fall through because many mortgage lenders will be reluctant to lend.

Though some lenders will insist on seeing evidence that the house seller has put a knotweed treatment in place and that this is in progress for them to consider a loan.

And you may find that some mortgage lenders will not be interested in lending until the knotweed has been eradicated completely.

If your buyer is struggling to find a lender, you may need to find a cash buyer who is happy to treat and remove the knotweed.

So, if your property has Japanese knotweed, you need to remove it.

Don’t attempt to cut corners when trying to do this on the cheap because you need to be sure that the problem has been resolved.

Don’t try manually removing the plant by yourself. In some cases, this attempt can exacerbate the growth of the invasive species (Hocking et al., 2023).

Knotweed needs to be professionally removed so it does not come back.

Usually, there is an insurance-backed guarantee from the firm carrying out the work that your property’s knotweed problem has been dealt with to help protect the integrity of the vendor for a few years afterwards.

It’s at the conveyancing stage that this guarantee will help protect the seller should legal action follow after the sale.

Also, having filled in the TA6 form will help protect you if you have found and then removed knotweed so if there is a detrimental effect on the property afterwards means you will avoid legal action for misrepresentation of the sale.

It’s also worth noting that a home buyer report for new builds may also flag up issues of what a surveyor believes is an urgent and necessary action, including dealing with Japanese knotweed.

And, from a legal point of view, you may believe that you can pretend that knotweed was not present on your property when being sold but when a buyer finds out afterwards, a professional will be able to determine how old the knotweed is – and the buyer could then hand you a hefty misrepresentation claim and a court appearance.

Even if your knotweed problem was treated professionally years beforehand, there is still a legal requirement to disclose that your property has been affected by knotweed.

This is often referred to as the ‘Japanese knotweed stigma’ and for years afterwards it will have an impact on the price of the property – even after the knotweed situation has been resolved.

New claims have opened doors for buyers of properties stricken with the Japanese knotweed stigma. For example, a south Wales homeowner sued the Bridgend County Borough Council after the invasive species made its way into his property from the county-owned cycle lane.

The court awarded the homeowner £4,900 in damages, citing a valid concern over the property’s loss of value.

Who can carry out a Japanese knotweed survey?

When you need to find a surveyor who is able to carry out a Japanese knotweed survey, you should consult the Royal Institution of Chartered Surveyors (RICS).

That’s because the organisation has four categories that dictate how dangerous the presence of Japanese knotweed will be.

This is the official guidance that building societies, banks and also mortgage lenders will refer to when looking at the issues of knotweed in a property.

The guidance makes clear:

Category one

Japanese knotweed has not been seen on the property, but it can be seen on a nearby home or on land that’s more than 7 metres from the property’s boundary.

Category two

As with category one, the Japanese knotweed has not been seen within the property’s boundary but was seen on a neighbouring land or property and within 7 metres of their boundary – but not more than 7 metres from habitable space, including a garage or conservatory of the subject property.

Category three

Knotweed is within the property’s boundary. It’s more than 7 metres from a garage, habitable space or conservatory. Any damage to outbuildings and structures or paths, fences and boundary walls, is minor. This category also makes clear that further investigation by someone who is suitably qualified is required.

Category four

This is the most serious category, and the knotweed is within 7 metres of a property’s habitable space, garage or conservatory and within the property’s boundaries or a neighbour’s property. The Japanese knotweed is causing serious damage to drains, paths, outbuildings, fences and boundary walls. Again, further investigation by a suitably qualified person is required.

Getting a mortgage on a property with Japanese knotweed

Sometimes it might be hard to get a mortgage on a house that is infested with Japanese knotweed.

For a property that has Japanese knotweed, the price of that property must be established first for a mortgage to be released.

However, to help price the house, the management plan for dealing with Japanese knotweed must be prepared by a Property Care Association-approved company.

In most cases, this plan will cover five years which will include two years of assessments to ensure there is no evidence of knotweed regrowing.

It’s also important that the company dealing with the knotweed issue should offer a guarantee against their work.

This knotweed management plan will then be offered to the lender and some lenders may be expecting that the knotweed treatment begins before conveyancing – while other lenders will insist it begins at another stage in the purchase process.

It’s worth appreciating too that specialists in dealing with Japanese knotweed have lots of experience in helping homeowners through the mortgage process and onto the exchange of contracts.

The law and Japanese knotweed

When it comes to selling a house with Japanese knotweed, it’s important that you understand the law.

Firstly, Japanese knotweed is not recognised as an issue legally – but it depends on circumstances.

The Environment Agency states that ‘it is not an offence to have knotweed on your land’.

However, if a neighbour’s land or property does have a knotweed problem and they are not bothering to act on it, then your property rights can be affected.

This will be called a ‘private nuisance’ because the neighbour’s inaction will have an impact on the selling and buying process of your property, as well as affecting the mortgage application process.

How to deal with Japanese knotweed when selling your home

There are some steps you can take when selling your home and understanding how to deal with Japanese knotweed.

Firstly, though, you need to know that knotweed is very difficult to kill, and you will, most likely, need the skills of a professional.

That’s because herbicides tend not to work, and you’ll need a professional firm with heavy machinery to remove completely the knotweed because the plant can regrow from tiny pieces that are left behind.

It’s also best to be upfront with an estate agent so that they can highlight the knotweed issue with a potential buyer.

  • Establish the problem: The first step is to have a professional survey undertaken by a specialist so they can properly identify the issue following the guidance set down by RICS. They will put a plan together to deal with the problem.
  • Establish who is responsible: When buying a property that has Japanese knotweed, you need to understand what your legal responsibilities are. Firstly, you must stop it from spreading to neighbouring properties and land before it becomes an expensive legal issue for you. If the knotweed originates from a neighbouring property or land, then you need to resolve the problem amicably – so use good communication skills!
  • Understand the damage: You need to understand the extent of the damage that the Japanese knotweed has caused because this could potentially affect your property’s price – or make it unsellable. Knotweed damage can be extensive, with underground roots growing several metres into the property’s foundations and drains. Having a professional survey done will reveal the extent of the problem.
  • Find someone to deal with Japanese knotweed: Find survey experts who deal with Japanese knotweed problems, and you should choose one that is a member of the Property Care Association (PCA).

What to do when selling a house with Japanese knotweed

The most important lesson to take from this Property Road article when selling a house with Japanese knotweed is to act as soon as you can, rather than later.

Firstly, by acting promptly you will be reducing the risk of causing long-term damage to your property, as well as to your neighbours’ properties.

Leave your action too late, and you may struggle to sell your home in future.

Essentially, when selling a home, you need a Japanese knotweed treatment plan in place for its removal and to deal with experts to ensure that it is done properly so there is no risk of knotweed returning.


  • Steve Lumley

    Steve Lumley has years of experience writing about property. His output has covered everything from property investment, news for landlords and student tenants to articles on how to run a successful portfolio and starting out as a property investor. He has also written several books on the subject.

    View all posts
  • Paul James

    Paul James, is a marketing expert with a passion for property. As well as being a property investor, Paul has also worked within the marketing departments of some of the UK’s leading estate agents. Paul is the founder of Property Road.

    View all posts
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