Mortgages for properties with Japanese knotweed

Japanese knotweed can cause major damage to your home. Learn how it can affect your mortgage and ability to claim on home insurance, as well as what you can do to treat it.

Eve Powell
Eve Powell
Updated 9 June 2022  | 3 mins read

Key points

  • Japanese knotweed spreads quickly and can cause major structural damage to a property
  • It’s usually more difficult to get a mortgage on a property affected by knotweed
  • Most lenders have a seven-metre knotweed rule and strict criteria you must meet
  • You’ll need to use a specialist to make sure it’s treated effectively and safely

What is Japanese knotweed?

Japanese knotweed is a type of invasive plant that grows rapidly and in doing so can ruin a garden and take over all other plant life.

Most importantly, its root structure - which goes deep into the ground and can spread out over several metres - can damage the foundations of your home, cause cracks in your brickwork and block underground drains.

What does it look like?

Japanese knotweed grows in large clumps of bamboo-like canes with purple spots and can be more than two metres high.

It has light green heart-shaped leaves and grows clusters of creamy white flowers in the late summer.

From late autumn, the plant dies back although the dead canes can take years to decompose.

In spring, Japanese knotweed starts growing fleshy reddish shoots from its roots called rhizomes. These are incredibly strong and can even break through tarmac and concrete.

If just a tiny part of a rhizome or stem is left in the ground, a whole new plant can grow and spread from it and start to wreak havoc all over again.

Can I get a mortgage on a property with Japanese knotweed?

It’s usually more difficult to get a mortgage if your home has Japanese knotweed, but it’s not impossible.

Your chances of success largely depend on the lender and the extent to which the plant causes a risk to your property.

Mortgage lenders will need to assess the suitability of your property for a mortgage based on their own policy around Japanese knotweed - and some lenders are more flexible than others.

Why does Japanese knotweed affect my mortgage chances?

Japanese knotweed can cause major damage to properties, potentially making them unstable and very expensive to repair.

And even when knotweed appears to have been destroyed, it can lie dormant only to be revived when the soil is disturbed - for example, if you started to lay a patio or build an extension.

Plus, a property with a history of Japanese knotweed can be much harder to sell.

It’s reasons like these that mean many lenders don’t view properties with a knotweed problem as good security for a mortgage investment.

How do lenders judge the severity or risk of Japanese knotweed?

Lenders differ on how they view Japanese knotweed and they’ll have their own criteria on how they assess the risk, but typically this involves a ‘seven-metre rule’.

Lenders usually have four categories of increasing risk:

  1. Japanese knotweed isn’t on the property but can be seen on a neighbouring property, or an empty space like a railway bank, which is more than seven metres away from the boundary

  2. The knotweed is within seven metres of your property boundary but not found within it

  3. It’s within the boundaries of the property but more than seven metres from a living space. If this is the case, it will need to be investigated by a qualified professional

  4. Japanese knotweed is within seven metres of the property and is causing damage to boundary walls, drains, paths and outbuildings. This is the most severe level of risk and immediate professional action will have to be taken to destroy it

Detecting knotweed in surveys and valuations

Qualified surveyors who are members of the Property Care Association (PCA) can examine the Japanese knotweed and categorise its risk according to criteria set by the Royal Institution of Chartered Surveyors (RICS).

Although not all surveys are carried out to the same standard. Generally, the more you pay for a survey the more meticulous the assessment of the property will be.

A mortgage valuation on its own won’t usually be enough to identify knotweed compared to using a registered independent surveyor. This is because its primary purpose is to make sure the property’s worth the amount of money the buyer’s asking to borrow from the lender.

This means you shouldn’t rely on a mortgage valuation to pick up any hidden problems like knotweed.

It’s illegal to sell a house with knotweed, so if your survey doesn’t detect it - but knotweed is discovered after the sale’s gone through - you could be entitled to compensation to cover the costs of removing it.

What kind of mortgage can I get if the property has knotweed?

This will depend on which of the four categories your property falls into - the more severe the category the more difficult it will be to find a mortgage.

If your survey discovers knotweed, you’ll need to have another survey done by a knotweed expert to determine the extent of the problem.

Even if the plant isn’t found on your own property but it’s on a neighbour’s land or several gardens away, a mortgage application may still be refused.

If your property is in category two or three, the lender might ask you to provide a bigger deposit or charge you a higher interest rate.

And many lenders will refuse your application if your property rates as category three or four.

Other mortgage providers will only lend on the condition that you legally agree to have the problem professionally treated, which usually includes providing a 10-year guarantee that the weed has been destroyed.

All the same, it can cost thousands, and even tens of thousands of pounds to effectively treat and destroy knotweed.

Do lenders’ policies change?

Recent research has indicated that Japanese knotweed might not be any worse for property, and may even pose less risk than many trees and woody shrubs.

In 2022, RICS published updated guidance that recommended a more lenient approach than the seven-metre rule, so that surveyors can use their own discretion.

Mortgage lenders have yet to respond to the updated guidance, but it’s hoped that in time, they’ll move their knotweed policies in line with the new advice.

How do you treat Japanese knotweed?

To treat Japanese knotweed effectively and safely you’ll need to use a specialist knotweed removal service.

There are three main levels of treatment that can be used:

Weedkiller control

This treatment can take several years as a weedkiller is expertly applied over time to kill the plant off in stages

Sealing the knotweed with a barrier

This involves partly digging out the plant for treatment, and then laying a knotweed barrier over it to prevent further growth

Root and branch removal

This involves excavating the plant completely and treating the ground using herbicides. As knotweed is classed as controlled waste, anything you dig up must be disposed of in licensed landfill sites

Does home insurance cover Japanese knotweed?

Most home insurance policies won’t cover Japanese knotweed and will exclude any damage it might cause.

Home insurance won’t cover you for problems that are a result of poor maintenance.

So if knotweed is discovered on your property, it’ll be down to you to pay for treating it and repairing any damage, like subsidence, that it may have caused over time.

However, having Japanese knotweed shouldn’t affect the cost of your home insurance premiums because your insurer’s unlikely to cover it anyway.

While you don’t need to declare knotweed to your insurer, if they ask you about it, being honest is important so that you don’t invalidate your policy.

Can legal cover help me if my neighbours take action?

If your neighbour’s property is damaged by Japanese knotweed that came from your property, you’ll be held responsible.

This means they can legally claim compensation if they can prove it came from your home.

If you’ve chosen legal expenses cover as a policy add-on, your home insurance may cover you for costs if your neighbours take legal action against you.

How can indemnity cover help with knotweed?

It’s also possible to take out indemnity insurance if Japanese knotweed hasn’t been discovered at your property before.

This type of insurance can protect you against possible future infestation and can help to pay for a specialist survey and treatment.

Does Japanese knotweed affect house prices?

Yes, because of the costs associated with Japanese knotweed - whether that’s from treating it, repairing the damage it causes, or both - property values can be affected.

Its presence on a property will likely put off the majority of potential buyers completely.

For those buyers still prepared to buy, most will want to negotiate a discount because of the presence of knotweed.