If you’re buying a property where the seller or agent have highlighted the presence of Japanese knotweed, or if it’s something that a property survey has uncovered as part of a survey, you should seriously think about the implications of proceeding with your purchase.

It is described by the Environment Agency as “indisputably the UK’s most aggressive, destructive and invasive plant”.

This highly invasive plant is extremely difficult to remove completely, it thrives in almost any condition, and can cost thousands and take a great deal of time to have it eradicated by professionals.

Even when all the evidence suggests it has been removed completely, the smallest of remnants can see it return with just as much aggression.

It is also the property owner’s legal responsibility to ensure it doesn’t spread to neighbouring properties – the implication of not adhering to this could mean facing a substantial legal fine.

What is Japanese knotweed?

For those unfamiliar with this plant, Japanese Knotweed is an incredibly aggressive weed that spreads rapidly, can cause structural damage to property and can grow by up to 10cm every day.

The bamboo-like plant is native to Japan, China, Korea and other Asian countries and was brought to the UK in the early 19th century.

While the presence of Japanese knotweed doesn’t have to be a deal-breaker when buying a property, you should be aware of the task in hand should you take it on.

If you’re looking to sell a property that is known to have an infestation of Japanese knotweed you should seek a professional service to carry out a treatment plan. As with any property related transaction, you should ensure that you do your research before agreeing to anything. More information on Japanese Knotweed can be found here.

Furthermore, you will also need to prove to prospective buyers as well as their mortgage lender that you have a professional, insurance-backed, management plan in place to ensure the complete eradication of the weed.

As a buyer, you should be aware that lenders are very cautious when lending on a property that has Japanese knotweed.

How does Japanese knotweed affect a property?

The risks to a property if left untreated can be costly, as Japanese knotweed can cause damage to a building’s structure, breaking open cracks in foundations, brick walls, and causing damage to sewage and drainage works.

It can also hinder future development work carried out on a property (for example, an extension), as only properly licensed organisations may remove contaminated soil waste from a property with a Japanese knotweed infestation, and it must be disposed of at an appropriately licensed waste facility. This would of course incur additional costs to any proposed project.

What’s more, because of the stigma and associated problems associated with the removal of Japanese knotweed, its presence is known to hurt house prices.

As a seller you are required to declare it to a buyer on a TA6 form. It is imperative that you make sure you are upfront with your estate agent from the outset as to the presence of Japanese knotweed. They will need to make any potential buyers aware of the presence of Japanese knotweed – it is a known cause for buyers pulling out of transactions if it is identified further down the line in the transaction.

How does the presence of Japanese knotweed affect a person’s ability to secure a mortgage?

Most lenders have a policy in place if Japanese knotweed is present, either within the grounds of the property you’re purchasing or nearby. However, mortgage lenders typically use a four-tier framework created by RICS to weigh up their decision to offer you a loan.

Risk category What this means for your property


Risk category What this means for your property
1 Knotweed is found more than seven metres away in a neighbouring property, or an empty space like a railway bank or wasteland.
2 Knotweed is within seven metres of your property but not within it.
3 It is within the boundaries of the property but is within seven metres from a living space. You will need a professional opinion.
4 The worst. It is within seven metres of the living space and/or causing damage to walls, paths or foundations. This needs immediate professional intervention.

*Source: www.which.co.uk

If the risk category falls within the 1-2 bracket you may find the number of lenders available to you decrease. While risk 3-4 would see more lenders withdraw their offer or ask for a bigger deposit/charge a higher interest rate.

If a lender were to accept you for a mortgage on a higher risk category as part of their lending criteria, they may also ask for an independent examination to be carried out as well as an ongoing treatment plan to be put in place.

Potential changes to the framework in the future:

As a result of an independent report, in 2019 the government’s Parliament’s Science and Technology Committee issued a report suggesting lenders are being too harsh about the weed.

The independent research concluded that Japanese knotweed may not be any more harmful than other plants or trees that don’t have the same controls.

Therefore, there could potentially be an update to the framework used by lenders to decide on a mortgage for a property that has Japanese knotweed.

For more information, we suggest a look at the current report and guidelines issued by the Royal Institution of Chartered Surveyors (RICS) on the Japanese knotweed and its impact on properties.

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