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Japanese knotweed insurance

How Japanese knotweed affects your home insurance

published: 31 January 2023
Read time: 10 minutes

Japanese knotweed can cause massive structural damage to your home – and affect your ability to claim on your home insurance

Left unchecked, Japanese knotweed can destroy your home’s foundations, drainage systems, and walls.

It grows incredibly fast – up to 20cm a day – and has deep, wide-ranging roots that can tunnel through tarmac, making it extremely difficult to kill. In short, it’s one plant you definitely don’t want in your garden.

Find out how to spot and tackle this vegetative threat to your property, and learn more about its impact on home insurance, mortgages, and house prices.

What is Japanese knotweed?

Japanese knotweed is a herbaceous plant with a bamboo-like stem and large green leaves. Introduced to the UK in 1825 as an ornamental plant, it spreads very quickly and can grow more than two metres high. Homeowners dread finding Japanese knotweed near their homes because its extremely strong and fast-growing roots can spread seven metres in all directions and cause massive damage to walls and buildings. You won’t be covered by Japanese knotweed insurance within your home insurance policy, so maintenance is important to avoid running into a problem.

Japanese knotweed

What does Japanese knotweed look like?

It’s easy to confuse this plant with other types of plants, so ask an expert before you panic about not being covered by Japanese knotweed insurance. You can check if you have Japanese knotweed by sending a photo to the Royal Horticultural Society.

Japanese knotweed features to look out for include:

  • Red or purple shoots that appear in March or April

  • A hollow, bamboo-like stem that shrinks and turns brown in the autumn months

  • Large, smooth, heart-shaped leaves that zigzag up the stem

  • Clusters of small, creamy white flowers that appear between July and October

How can Japanese knotweed damage my property?

Japanese knotweed can take over your garden and cause significant structural damage to your home, so maintenance is essential, as you won’t be covered for Japanese knotweed insurance within your home insurance policy. It spreads via its roots, which are extremely tough and can shoot out by up to seven metres in any direction. These roots penetrate tarmac and can therefore rip through drainage systems, cause walls to crumble, destroy outbuildings like sheds, and even compromise the foundations of your home.

That’s why the Royal Institution of Chartered Surveyors views knotweed as a potential risk if found within seven metres of your house. The potential for damage is so severe that you could be sued if Japanese knotweed is found to have spread from your garden to your neighbour’s land. However, the good news is, you can prevent Japanese knotweed from causing damage by taking action to remove it.

How can I get rid of Japanese knotweed?

Japanese knotweed is notoriously difficult to destroy, and as you won’t be covered by Japanese knotweed insurance, you want to avoid reaching the point of attempting to kill it by keeping an eye out. It also dies back to ground level in the winter, meaning it can be hard to tell whether it’s really gone or not. But if you want to try to tackle it yourself, you can use a glyphosate-based weed killer designed to target Japanese knotweed (the Royal Horticultural Society suggests Roundup Tree Stump). However, be prepared to keep treating the plant for several years to kill it completely.

Other Japanese knotweed removal options include:

  • Hiring a professional contractor – this is the easiest way to ensure you get rid of Japanese knotweed for good. It’s also the only way to get an insurance-backed guarantee or residential Japanese knotweed indemnity insurance policy, which you’ll probably need to get a mortgage if Japanese knotweed turns up on your property survey. Methods include excavation and spraying with professional-grade glyphosate weed killers, with costs ranging from about £3,000 to £10,000 or more.

  • Digging it out yourself – this will not only be hard work, but it’s also unlikely to provide a lasting solution. You’ll also have to dry it out and burn it or dispose of it at a licensed landfill site because Japanese knotweed is classified as ‘controlled waste’ under the Environmental Protection Act 1990. If you choose to put it in a landfill site, you’ll have to pay the government’s landfill tax and use a specialist company to transport it. Again, this could cost several thousand pounds.

Does my home insurance cover Japanese knotweed?

Most buildings insurance policies exclude damage caused by Japanese knotweed. If the knotweed problem comes from your garden, any claim is likely to be refused, as you’ve been negligent by failing to take measures to protect your home. If your home is affected by Japanese knotweed on adjacent land, your insurer will probably pursue the land’s owner for the related costs.

You’re also unlikely to be able to make a claim for treating or removing knotweed unless you take out a specialist Japanese knotweed insurance policy prior to spotting the plant. But don’t delay getting rid of Japanese knotweed – as the plant grows, both the cost of treatment and the likelihood of bigger problems will increase.

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

You don’t have to tell your insurer there is Japanese knotweed on your property unless they ask – in which case, you must tell the truth. If you don’t, you could invalidate your entire home insurance policy.

Will Japanese knotweed increase my insurance premiums?

Most insurers will refuse to pay out for Japanese knotweed claims anyway, so having the plant growing on your land shouldn’t affect how much you pay for home insurance. However, your insurance company will expect you to take measures to protect your home and other people’s property by keeping the plant in check. That’s why removing it completely is the most suitable option.

Will Japanese knotweed affect the value of my home?

Rampant Japanese knotweed will almost certainly reduce the value of your home. So, if you’re hoping to sell, you have yet another reason to remove the plant from your land. Just cutting it back isn’t enough, as it will usually be spotted on the surveys conducted for potential buyers and their mortgage lenders; the only real solution is to get to the root of the problem.

Will Japanese knotweed affect my mortgage?

You may struggle to get a mortgage if you live in, or are hoping to buy, a property affected by Japanese knotweed. If, for example, the plant is spotted on the property survey completed as part of your mortgage application process, your bank or building society will probably insist a professional attend to remove it before approving your mortgage. As a buyer, you could use this as a bargaining tool to reduce the price you pay for the property. Just remember to double check that the plant has been totally removed before going ahead with the purchase.

Is it illegal to have Japanese knotweed in my garden?

It’s not illegal to have Japanese knotweed growing in your garden, but you could have problems if you fail to take action to control it. You might even be issued with an ASBO ordering you to ‘control or prevent the growth of Japanese knotweed’. Failing to act on this order would be a criminal offence and could even result in a £2,500 fine.

If you’re caught spreading Japanese knotweed in the wild, meanwhile, you could face a £5,000 fine and up to two years in jail.

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

You’ll be held responsible for any damage caused by Japanese knotweed that spreads to other people’s property from yours. This means that your neighbours can seek compensation for any damage caused by the weed, as long as they can prove it came from your property. These claims can be worth thousands of pounds, so it’s a good idea to act quickly if you spot Japanese knotweed in your garden.

If you have legal expenses cover alongside your home insurance, you may be able to claim for the legal costs involved in a neighbourly dispute about Japanese knotweed – just make sure you check what’s covered before you start.

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