Should I buy a house with Japanese knotweed?

Key takeaways 

• Japanese knotweed is a fast-spreading plant that can cause significant damage to properties 

• Most buildings insurance policies exclude damage caused by Japanese knotweed. 

• RICS categorizes the severity from A to D; more severe cases (A or B) may hinder mortgage approval without a management plan 

• Eradication can cost between £950 and £4,000 and take 3 years or more 

Should I buy a house that has Japanese knotweed? 

You should get a Japanese knotweed survey done before buying a house with Japanese knotweed. You should use the information in the survey to make an informed decision about buying the property. 

The severity of its invasion can affect how likely you are to get a mortgage. You should also be aware that home insurance is unlikely to cover damage by Japanese knotweed. 

Sellers must disclose if there is a Japanese knotweed problem. And if there is, they must also provide a plan from a specialist detailing how bad it is and how it can be dealt with. 

Will Japanese knotweed affect my mortgage? 

Yes, Japanese knotweed can affect a mortgage or remortgage application.  

Mortgage companies are concerned about Japanese knotweed because, over the course of a mortgage’s life, it could cause substantial damage if not controlled. 

Getting a mortgage with Japanese knotweed on the property isn’t impossible but you will usually need to have a comprehensive plan for its removal in place.  

What is Japanese knotweed? 

Japanese knotweed – aka fallopia japonica or reynoutria japonica – is a plant native to Japan, China, and Korea. 

It was brought to and planted in European gardens years ago because it’s a rather pretty bamboo-like plant. But unfortunately, it’s one of the world’s most invasive species, and is now controlled under UK law.

This can present a few problems if you’re buying or selling a home that has Japanese knotweed. It can also affect the cost of your home insurance.  

You can recognise Japanese knotweed by its big, heart-shaped leaves, and tall stalks that look a little like bamboo with ‘knots’ along them, which have a pink or red tint. It casts strong roots in the ground and can grow over seven feet tall. 

See a gallery and read more on the Royal Horticultural Society website. 

Why is Japanese knotweed bad? 

Japanese knotweed is invasive, fast growing, and very difficult to get rid of. And, worst of all, it can cause damage to your home and to the ground. 

Its roots are large, strong, and grow very quickly – and where they spread out, they can damage walls, floors, foundations, and even roads.

It also suppresses other plant life where it grows, which can be a problem for gardens and for basic biodiversity. 

Most buildings are safe from damage, as are the kind of substantial foundations you find on a house. But Japanese knotweed can still cause problems for less robust structures and foundations, such as greenhouses, conservatories, boundary walls, garages, and sheds.

All of which can be costly to deal with. Thankfully, Japanese knotweed isn’t quite as dangerous as we once thought, so rules have relaxed a bit in recent years.

But UK law still lays out how it must be controlled, as it’s still a weed known for being invasive and causing issues – not least because it’s so tough to remove. See the full guidance and rules for Japanese knotweed on Gov.uk. 

What is a Japanese knotweed survey? 

A Japanese knotweed survey is a specialised inspection that identifies the presence, extent, and potential future risks of Japanese knotweed on a property. 

RICS, the organisation that sets the standards for home surveys,  set out new guidance on how surveyors should report Japanese knotweed in 2022.

It’s a sliding scale that tells you how bad the invasion is, and gives buyers (and mortgage lenders) an indication of how tough it might be to manage. A survey will categorise knotweed in the following ways: 

If the survey reports category A or B, lenders will be reluctant to offer a mortgage on the property until there is a plan in place to manage the infestation.

The seller will need to arrange a specialist’s report. Category C or D is less likely to affect your ability to get a mortgage.

But you should still pay attention to what it says, and be prepared to tackle the problem. Ask for your solicitor’s advice – you may be able to negotiate a lower price, or require that the Japanese knotweed is dealt with before you move in. 

Remember that if it’s present on your property, you’re legally required to do what you can to keep it under control. 

Can I sell my house if it has Japanese knotweed? 

You can sell a house with Japanese knotweed without falling foul of the law. But you’ll need to disclose the problem as honestly as you can. 

There’s a section on the TA6 form where you can fill this out. 

A good course of action is to hire a specialist and get a full report and plan, detailing how bad the problem is and how it can be dealt with. Buyers will most likely require this in order to get a mortgage anyway. 

A better course of action is to start dealing with knotweed before you put your house on the market. This can be costly – usually between £950 and £4,000, depending on the scale of the problem – but can raise the value of your property overall. 

How to get rid of Japanese knotweed 

You shouldn’t treat knotweed yourself unless you have the appropriate skills and experience. You can find companies that specialise in treating knotweed. 

Experts will normally use glyphosate-based weed killers to treat knotweed and stop it spreading.  

It usually takes at least 3 years to treat Japanese knotweed. Knotweed rhizome can remain dormant in the soil for many years and will regrow if disturbed or if the soil is relocated. 

Japanese knotweed requires careful disposal due to legal regulations surrounding the plant, as Japanese knotweed is classified as ‘controlled waste’ under the Environmental Protection Act 1990. 

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