Japanese Knotweed and Buildings, Mortgages and Insurance

What is Japanese knotweed, how does it affect my property, can I get insurance if my house has Japanese knotweed, can I get a mortgage if a house has Japanese knotweed

This news article is intended to provide general advice about insurance of property affected by Japanese knotweed and the effect it can have on mortgages and insurance. WE DO NOT PROVIDE QUOTATIONS FOR THIS CLASS OF BUSINESS but the information contained in this article may assist you in finding a buildings insurance policy for your property.

What is Japanese knotweed?

Since its introduction to the UK in the 1840’s, Japanese knotweed (initially considered an ornamental plant) has been quietly spreading throughout the UK. Now the true extent of the invasion of this plant is known and pretty much the whole of the UK has an infestation.

Japanese Knotweed and buildings, mortgages and insurance

How does it affect my property?

Japanese knotweed is an arguably attractive plant that can grow at a phenomenal rate. It can grow a meter in height in only 3 weeks and is in the top 100 of the World’s most invasive plants! Eradication efforts in the UK alone cost £150m per year so this is no walk in the park. The root systems for a plant 2 meters high can spread 2-3 meters under the ground laterally.

Clearly not good for the native plants it annihilates but what does it mean for property owners?

Can I get a mortgage if a house has Japanese knotweed?

If you are considering purchasing a property with a Japanese knotweed infestation, or even a single plant for that matter, you may not be able to secure a mortgage. Because of the ferociously invasive nature of the plant, if the infestation is left untreated this plant will take over your garden and damage your property. Lenders have been known to withdraw a mortgage offer if signs of knotweed are visible at the property citing insurance problems as the main reason for their reluctance to lend. There is no doubt that a severe infestation of this plant will significantly reduce the market value of any property it blights and surveyors now look for signs of this plant during their property inspections.

Can I get insurance if my house has Japanese knotweed?

If you are looking for buildings insurance for a property with Japanese Knotweed, you need to be cautious about the extent of the plant growth and whether it has caused, or is causing damage to the property. You need to take advice as to whether or not is is a requirement to disclose the existence of the plant to your insurer (unless specifically asked) but you are under an obligation to do everything you can to prevent damage to your property caused by the plant. In the event of a claim, your insurer may investigate this and if you have not done everything possible to prevent the loss occurring then they may refuse to pay a claim citing that your inactivity to control a plant on your property led to the damage occurring.

If an insurer learns of an infestation of Japanese Knotweed they may either cancel the insurance, not invite renewal of a policy or simply exclude the peril of subsidence, heave & landslip. The insurer we use for this class of business will (depending on the extent of the infestation) often provide quotes but will exclude subsidence, heave and landslip cover. Most lenders will insist on insurance cover for subsidence, heave & landslip as a condition of the mortgage so our policy will NOT be sufficient for the requirements of a mortgagee.


For any new requests for buildings insurance many insurers will very likely decline to offer a quotation altogether.

Do not underestimate the damage this plant can do to your property. It can grow through concrete, it can find a way through your floorboards inside your house, it can grow through a tarmac driveway. This plant is a true survivor and you must take every step possible to eradicate it if you suspect it is growing in your garden.

Control and Management of Japanese Knotweed

There are some specialist companies who can put in place a management programme for Japanese Knotweed which can be a very effective way of either eradicating it or preventing further growth. It is without doubt a very difficult plant to destroy but the key to solving this is speed. Don’t put off any treatment. If you suspect it, call in a specialist firm immediately, it will get much more serious if you leave it.

An internet search will provide you with a number of specialists in your local area who will be able to deal with the management of the ground. If you are unsure who to use, it may be wise to contact your local authority and ask them which specialist contractor they use for controlling the plant on their own land.

Update November 2014 – An amendment to the Anti-social Behaviour, Crime and Policing Act 2014 includes Japanese Knotweed and other invasive non-native plants. Full details of how these affect the homeowner will be published shortly

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