Japanese knotweed has long been a concern for homeowners, but the recent judgment in Downing v Henderson, which hit the headlines this week, highlights some of the problems it can cause particularly when it comes to buying and selling a property.

In this latest case, purchaser Jonathan Downing successfully sued the seller of a £700,000 house in South West London for misrepresenting whether there was knotweed at the property when he sold it.

Jeremy Henderson had answered ‘no’ to the question on the property information form (TA6 form) asking if the property had ever been affected by knotweed. Yet when Downing moved in, he found knotweed at the rear of the property. In court, Henderson claimed that he couldn’t see the knotweed due to a large bush, but actually, it had previously stood up to 2m tall and there was evidence it had been treated with herbicide. His defence was dismissed, with the Judge finding that he didn’t genuinely believe that the property was unaffected by knotweed at the time it was sold. Henderson now faces a legal bill of £200,000.

Knotweed is a significant problem across the country. It spreads quickly and can grow up to 10cm a day with the roots extending up to three metres deep and seven metres laterally. It is strong enough to break through concrete and causes considerable damage to buildings and infrastructure. It’s estimated to be the cause of circa £170 million of home repairs every year and the government estimates the cost of eradicating it would be £2.6 billion. Moreover, it can devalue properties by 5-15% and in extreme cases completely devalue a property rendering it unmortgageable.

What should a homeowner do when selling or buying a property?

Sellers are obliged to respond to an enquiry on whether or not their property is affected by knotweed on the TA6 form as part of the sale process. This enquiry was revised in February 2020, so now homeowners can only answer ‘no’ if they are absolutely certain there is no knotweed in, or within 3 metres of, the property boundary. If a seller is unsure if knotweed exists or previously existed they should always tick ‘not known’ on the TA6 form.

If the property has been or is affected by knotweed, the seller must declare it on the TA6 form. As Downing v Henderson confirms, the court will not look favourably on a seller dishonestly answering this enquiry.

A buyer should always get a survey carried out and ensure it includes the garden and, where possible, gardens of adjoining properties. This applies to flats as well, since the presence of knotweed could affect the structure of the building and the cost of remedial works could result in a significant increase in service charge payments. Recent case law has strongly reinforced the legal precedent that surveyors must fulfil their duty of care to a buyer by identifying the invasive plant and if they fail to do so, they could be sued for negligence.

However, developers and builders are not obliged to complete the TA6 form so if they are the seller, the buyer should make sure their solicitor asks specific enquiries to get confirmation of the current and historic knotweed position.

Are homeowners liable for knotweed spreading to adjoining properties?

Knotweed must be dealt with straight away. If a homeowner fails to do this, they could face a hefty claim from adjoining landowners. This claim could be for the costs of removing the knotweed but also for the decrease in value of the adjoining property.

In the recent case of Clarke & Kaye v Abbasi, a couple were sued by their neighbour for £250,000, with the neighbour claiming that knotweed from the couple’s house had affected the footings of their property. They sought ‘damages for nuisance for the encroachment of knotweed’ on their land. They argued it devalued their property and they were unable to obtain mortgage finance because of the knotweed.

We are seeing an increase in these types of cases and recent judgments raise the possibility of similar claims being made more frequently in the future.

Can homeowners get insurance against knotweed?

Whilst most buildings insurers don’t ask about knotweed, they may not cover any treatment so homeowners should check their insurance policy carefully to see if it is covered. A mortgage lender may also not be willing to lend if the buildings insurance policy doesn’t cover knotweed.

Indemnity insurance cover can be taken out to provide protection for buyers and mortgage lenders if knotweed is discovered. This will generally only be available if no knotweed is present or if it’s been successfully treated in the past. This insurance could cover the cost of a survey report to confirm the presence of knotweed, the cost of treatment, repair of any damage and could extend to defending any legal proceedings in the event of any third party being affected.