What to check before buying a home with Japanese knotweed.

Close-up of Japanese Knotweed leaves

Property affected by Knotweed could stop you from getting a mortgage, and can be difficult to insure or sell. There are solutions, however.

This article looks at the issues involved with buying a house with Japanese Knotweed, and considers the impact of the new guidance issued in 2022.

See also:

Japanese Knotweed? What to do before selling your home.

What is Japanese Knotweed?

Japanese Knotweed ('Fallopia Japonica' to botanists.) is a highly invasive plant that has received much negative press over the past decade.

The plant's roots can cause damage to property, so its presence nearby is a concern to home buyers and mortgage lenders.

Reported problems with Japanese Knotweed include:

  • Damage and blockage to drains and other buried services.
  • The collapse of boundary or garden walls.
  • Buckling and other damage to drives, patio and similar paved areas.
  • Damage to the foundations of conservatories, outbuildings and even house foundations (especially older properties which often have shallow foundations).

Bamboo like plant

Japanese Knotweed is a bamboo-like plant that was introduced into the UK in the 19th century as an ornamental plant. It became popular with landscape gardeners because it grows rapidly, covering large areas quickly.

It spreads by its underground rhizome system and can quickly travel from one garden to another. It is no longer confined to the large country gardens where it was originally introduced and can now be found in ordinary suburban gardens in many parts of the country.

Difficult to eradicate

Japanese Knotweed is extremely difficult to eradicate. Standard weed killer won't be enough to kill it.

It is very difficult to dig up. If a small piece is left in the ground it will rapidly spread again.

The Royal Institution of Chartered Surveyors (RICS) states that it would be necessary to excavate the ground completely up to 3m vertically and up to 7m horizontally from the above-ground growth, resulting in large volumes of waste soil.

Cost aside, excavating a large amount of soil is impractical in a typical residential garden - especially if the plant has spread to several properties.

The plant, together with the excavated soil, must be disposed of as 'controlled waste' in accordance with relevant regulations.

The alternative method of eradication is a chemical treatment, using a specialist herbicide applied by an approved contractor. However such treatment can take three years or more to be totally effective.

As the new owner, you will inherit the responsibility

There are potential legal consequences of owning a home with Japanese Knotweed. It a criminal offence under the Wildlife and Countryside Act 1981 to knowingly allow Japanese Knotweed to spread from your property.

Furthermore, the Anti-Social Behaviour, Crime and Policing Act 2014 provides that community protection notices can be used to force landowners to control non-native invasive plants (which includes Japanese Knotweed) on their property. Fines can be imposed for non-compliance with such notices.

You might not be able to get a mortgage

Most lenders simply won't lend on a property affected by Japanese Knotweed, unless certain criteria are met.

Individual lender requirements are published in the UK Finance Mortgage Lenders' Handbook.

At the time of writing. for example, the HSBC requires any property with Japanese Knotweed within the boundary or on neighbouring land within 7 metres of the habitable space to have:

  • A fully paid up treatment plan which has commenced with an appropriately qualified person or company such as an accredited member of an industry recognised trade association such as the Property Care Association and the Invasive Non-Native Specialists Association
  • A minimum 10-year insurance backed guarantee can be provided on completion of the works.

2022 - Japanese Knotweed update

Following a House of Commons report published in 2019, The Royal Institution of Chartered Surveyors (RICS) has published a new 2022 guidance note for chartered surveyors.

The guidance note abolishes the ‘7 metre rule’ used by surveyors and valuers, when assessing whether the presence of Japanese Knotweed poses a threat to a property.

The RICS guidance states that:

“The so-called ‘seven-metre rule’ focused more on what has been demonstrated to be an overstated risk of Japanese knotweed to buildings, rather than its sometimes-serious impact on amenity.”

“Research has demonstrated, and it is now generally accepted, that Japanese knotweed poses little or no risk of structural damage to robust buildings with substantial foundations such as dwellings, as opposed to less sturdy structures with shallow foundations, such as conservatories, garages or boundary walls,”

RICS have moved the dial and are now recommending that, in many situations, effective control can be achieved by the managed application of herbicides.

Valuers and surveyors are encouraged to consider potential Knotweed management outcomes, as opposed to the more rigid building proximity rules.

It is anticipated that mortgage lenders will revise their lending criteria accordingly.

Buildings insurance

It is also likely that any damage to buildings and drains will not be covered by buildings insurance. If there is Japanese knotweed on your property, you don't have to disclose it to an insurer, unless asked. However, it would invariably be a better policy to address the problem then contact your insurer for clarification.

Identifying Japanese Knotweed at a property before you buy it

Thoroughly inspect the garden

Make sure you are able to access the garden on any viewings and see if you can see any obvious infestations. If the agent or seller is with you on the viewing, ask if there are aware of the presence of Japanese Knotweed. They may just come clean at this point. If the vendor isn't there, ask the agent to ask the seller.

Bear in mind that its appearance changes over the seasons.

It is therefore recommended that you specifically ask sellers whether they are aware of the plant growing on their property or on neighbouring property.

Sellers are legally required to disclose Japanese Knotweed on the TA6 Property Information Form. However, you typically won't receive this form until you are weeks into the conveyancing process.

Get a survey

RICS Building surveyors have been advised to be 'alert' for the presence of Japanese Knotweed.

If you have concerns, it is that you commission a full building survey rather than a Homebuyer Report.

Be warned...

Some surveyors have been slow on the uptake where Japanese Knotweed is concerned. Some RICS surveyors are seemingly oblivious to the risk and still do not inspect the gardens thoroughly. It is advised that you commission a full Building Survey. Never rely on the mortgage valuation as a survey. In some cases, further inspection by a suitable expert may be required.

Before you instruct the surveyor, confirm that the garden will be inspected on the survey.

Should you pull out?

The existence of Japanese Knotweed does not necessarily mean that you shouldn't buy the property.

If there is an approved knotweed management and treatment plan in place, then there should not be any problem in getting a mortgage.

However, most lenders will also require:

  • A fully paid up treatment plan which has commenced with an appropriately qualified person or company such as an accredited member of an industry recognised trade association such as the Property Care Association and the Invasive Non-Native Specialists Association
  • A minimum 10-year insurance backed guarantee can be provided on completion of the works.

As soon as you discover Japanese Knotweed at the property, you should call your lender and ask what their position is. You can also check the UK Finance Mortgage Lenders' Handbook.

What if there isn't an approved knotweed management and treatment plan in place?

You can insist that the seller initiates and pays upfront and in full for the treatment program before exchange. The treatment company should be able to issue a 10-year insurance guarantee from the date of initial treatment. However, some firms still only issue guarantees after completion of the treatment plan, which may be 3 years in the future. This is a key point and you should ask the seller to check when the guarantee will start from

Alternatively (and assuming the lender agrees), it may be a question of agreeing on a reduction in the asking price to cover the cost of future treatment.

Speak to your solicitor

Get advice from your solicitor at the earliest possible stage. Solicitors deal with Japanese Knotweed situations all the time and their advice tends to be pragmatic. Early advice can save you a significant amount of time money in the long run.

Article by Completely Moved authors

The Completely Moved team have years of experience helping home buyers, sellers and owners, answering questions and providing property advice.

Share this article:

Sale & Purchase Conveyancing

Know exactly how much you'll pay, with an all inclusive, no move, no fee solicitor quote.
Get quotes for our services