Why is Japanese Knotweed such a problem?

There have been a recent spate of prominent media stories about the perils of Japanese Knotweed and how it can adversely affect a house sale. But what is this reportedly pernicious plant, and why is it such an issue when it comes to property?

David Keighley, Brevis Director & Head of Residential Property, shares his view.

Japanese Knotweed was introduced by botanists into Britain in the 19th century as an ornamental plant. It is widely believed that Victorian engineers used it to stabilise railway embankments. It is completely safe to touch and is edible. In fact, it is said to have quite a pleasant taste, reminiscent of lemony rhubarb. In Japan it is called itadori and is a prized spring delicacy.

So why is it now regarded as such a problem for home owners?

Knotweed spreads quickly and can grow up to 10cm a day with the roots growing up to three metres deep and seven metres across. It is strong enough to break through concrete and can cause considerable damage to buildings. It is estimated to be the cause of around £170 million of home repairs every year in the UK and the government estimates the cost of eradicating it would be £2.6 billion. So it is significant.

Knotweed is legally classed as a controlled plant under the Wildlife and Countryside Act 1981. It is not illegal to have Japanese knotweed on your property but you can be prosecuted if you allow it to spread outside your boundaries.

When you sell your house, you are obliged to answer questions on whether or not your property is affected by knotweed. This is covered by a question in the ‘TA6 Property Information Form’, which includes this note:

‘Japanese knotweed is an invasive non-native plant that can cause damage to property if left untreated. The plant consists of visible above ground growth and an invisible rhizome (root) belowground in the soil. It can take several years to control and manage through a management and treatment plan and rhizomes may remain alive below the soil even after treatment.’

The question then asks: ‘Is the property affected by Japanese knotweed?’ As a seller, there are three possible answers you can give: yes, no or not known.

If you are aware of knotweed on your property when you are selling, you are legally obliged in the TA6 form to answer ‘yes’. Your buyer must then be given a copy of any knotweed management plan you have in place, and evidence of any insurance cover. Knowing there is Knotweed present on your property may of course affect your buyers’ decision on whether to proceed with their purchase of your property or not. Or it could prompt them to ask for a reduction in the purchase price.

As a property seller, you can only answer ‘no’ if you are absolutely certain that there are no knotweed roots in the ground of your property or within 3 metres of its boundary. This is the case even if there are no visible signs above ground. So most sellers choose either the ‘yes’ or ‘not known’ options on the form.

But how serious can it be if you answer incorrectly? The answer is – very.
In fact, a recent court decision highlights how some judges will not look favourably on a seller if they dishonestly answer the knotweed question. When Mr Downing purchased a house in London from Mr Henderson, the TA6 form for the property included the answer ‘no’ to the knotweed question. But when Mr Downing moved in, he found knotweed in the garden. He therefore sued Mr Henderson for misrepresentation during the property sale.

As part if his defence in court, Mr Henderson claimed that he couldn’t see the knotweed due to a large bush in front of it. So he did not know of its existence. But during the case, experts proved that it had previously grown up to c. 2 metres tall. There was even evidence that it had been treated with herbicide.

The Judge therefore ruled that Mr Henderson had indeed misrepresented the facts when he said the property was unaffected by knotweed at the time it was sold. And Mr Henderson now faces a legal bill of £200,000.

So the message is clear – always answer truthfully on the paperwork when you’re selling your property!

And for buyers, make sure you get a survey carried out, and ensure it includes the garden. Where possible your survey should even include the gardens of adjoining properties too, to check for knotweed. The surveyor may not be able to categorically establish whether or not knotweed is present, so you may also need a specialist expert to get involved.

And for homeowners, whilst most buildings insurers don’t ask specifically about knotweed on or near your property, they may not cover any treatment if it is found. So you should check you insurance policy carefully to see if it is covered.

For further help and advice on the process of buying or selling a house, visit the Brevis Home Movers’ Guide.

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