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How Japanese knotweed affects your home insurance

Learn how Japanese knotweed can affect your property, what to do if you find it and which type of insurance might help.

Eve Powell
Eve Powell
Updated 26 November 2021  | 4 mins read

What is Japanese knotweed?

While it was originally brought into the UK as an ornamental garden plant, Japanese knotweed is now a well-known stubborn and destructive weed.

This plant pest can grow more than 20cm a day and can reach up to 10 feet high. Its deep roots can also stretch more than seven metres wide - making it very difficult to get rid of.

Its speedy growth can cause a whole host of problems from damaging tarmac, paving, and drains, to making the walls of your home unstable.

Key points

  • Japanese knotweed is a fast growing, invasive plant that can cause expensive structural damage
  • You’re legally responsible for ensuring it doesn’t spread to neighbouring properties
  • Without effective treatment it can reduce the value of your home and you could be liable for compensation claims from neighbours
  • It pays to act fast and use specialists to remove and safely destroy all plant waste

What does Japanese knotweed look like?

The plant starts out with small fleshy reddish purple shoots poking out of the ground. These grow into tightly packed together purple-flecked canes that look similar to bamboo.

Lush green shield-shaped leaves form that grow to around 12cm long, and these are topped with white feathery flowers in August and September.

The stems die back in winter but the dry canes stay around for several months.

What do I do if I find Japanese knotweed?

If you find Japanese knotweed on your property you don’t have to declare it or even treat it, but you are legally responsible for making sure it doesn’t spread onto any neighbouring land.

Acting fast can help minimise the damage and if you’re selling your property you’ll need to have a treatment plan in place.

It’s such an invasive plant that if it spreads into the wild you could face a fine of up to £5,000, or be sent to prison for up to two years.

For these reasons it’s best to get expert advice on how to control it and assess how your home may be affected.

How can I get rid of Japanese knotweed?

Its extensive root system means simply digging it out rarely works - even a tiny amount left in the soil can start the growth cycle over again.

Plus there are strict rules about how and where Japanese knotweed waste can be taken for disposal.

For these reasons, the safest and most effective way to get rid of Japanese knotweed is to use the services of a specialist.

Several applications of chemical herbicide will also need to be used. And to make sure the plant is completely destroyed, treatment and monitoring plans will usually span many years.

Can Japanese knotweed cause property damage?

Yes it can. As it seeks moisture, its roots can get into and expand small cracks in your brickwork, pipes and masonry.

Targeting your home’s weak points can cause damage to its foundations and retaining walls, making them unstable.

Japanese knotweed’s rapid growth can also swamp the other plants in your garden and greatly reduce the usable area of your outside space.

Does home insurance cover damage from Japanese knotweed?

Standard home insurance policies don’t typically cover the costs of repairing damage caused by Japanese knotweed.

Although you may be covered if you have a comprehensive buildings insurance policy and there’s damage to the structure for your building. For example, if it causes subsidence.

However, if it came from your garden, it’s unlikely you’ll have a valid claim if you hadn’t tried to treat and remove the Japanese knotweed before the subsidence happened.

Will my insurance provider pay for treatment of Japanese knotweed?

It depends on your policy, but most home insurance policies don’t cover the costs of treating or removing Japanese knotweed.

Typically, it’ll be down to you to organise and pay for the plant infestation to be dealt with.

Do I need to tell my insurer I have Japanese knotweed?

You won’t need to tell your insurer unless they specifically ask you. But if you’re asked it’s important to tell the truth so you don’t invalidate your policy.

However, as Japanese knotweed isn’t typically covered by home insurance, it’s unlikely you’ll be questioned about it.

Will Japanese knotweed increase my insurance premiums?

Because most home insurance policies won’t cover Japanese knotweed, having it at your property shouldn’t affect your premiums.

Bear in mind that if you make a successful claim for subsidence caused by Japanese knotweed, it’s likely your premiums will increase the following year.

And it might be difficult to get cover for subsidence at the same property in the future.

Will it affect the value of my home?

You’re legally obliged to say if there’s Japanese knotweed at your property when you’re selling it, and mortgage lenders will usually impose strict conditions if this is the case.

This might lead to buyers reducing their offer and it may even cause your sale to fall through.

However, putting in place an effective treatment plan by expert professionals can often bring your home’s value back up close to its market price.

What about my mortgage?

The risks to property posed by Japanese knotweed, and the chance of it growing back even when it’s thought to have been destroyed, can mean your mortgage application is declined.

Each lender has their own criteria for assessing the risk and severity of the problem.

This can range from the plant only being found at a nearby property, to it being within a few metres of your home and causing damage to paths, walls or foundations.

The lender could ask for a bigger deposit, charge a higher interest rate, or hold back money until it’s treated by an accredited specialist providing a 10-year insurance backed guarantee.

What if my Japanese knotweed damages my neighbour’s house?

You’re legally responsible for preventing the spread of the plant to your neighbour’s property. This means you’re also responsible for its effective removal and paying for any repairs.

It’s possible your neighbour could also claim compensation for their loss of enjoyment of their land or garden.

These costs could add up to thousands of pounds, so it pays to learn how to recognise Japanese knotweed and act quickly if you discover it on your property.

Will my insurance cover legal expenses if my neighbour takes action?

Some home insurance policies offer legal expenses cover as a standard feature. And if yours doesn’t, you can usually buy it as an optional add-on to your policy.

This cover might help with legal expenses if your neighbour tries to claim compensation for the spread of Japanese knotweed onto their property.

What insurance do I need to cover me against Japanese knotweed?

If Japanese knotweed hasn’t been discovered at the property before, it’s possible for you to take out indemnity insurance.

This type of insurance can provide protection against future infestation of the plant, and can include cover for the costs of a specialist survey and treatment.

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