Can You Sell A House With Japanese Knotweed?

Japanese Knotweed (Fallopia japonica) is an invasive non native plant introduced to the UK as an ornamental in the nineteenth century. It spreads aggressively through rhizomes (root structures) that can grow up to three metres deep and seven metres wide. It can cause structural damage to lightweight buildings, paving, and drainage, though the actual structural risk is often exaggerated.

The TA6 Property Information Form (the standard pre contract form completed by every UK seller) includes question 7.8: "Is the property affected by Japanese Knotweed?" The three answer options are:

• ●Yes
• ●No
• ●Not known

If you knowingly answer "No" when Knotweed is present, you can be liable for misrepresentation. The buyer can sue for damages or in some cases rescind the contract entirely. The 2018 Court of Appeal case Williams v Network Rail confirmed that even the presence of Knotweed within seven metres of a property (not on it) can affect property value and may need disclosure.

"Not known" is the safest answer when you genuinely do not know. Most buyers will then commission a survey or specialist inspection.

Most high street lenders will lend on a property with Knotweed provided three conditions are met:

• ●A professional management plan is in place from a registered Knotweed contractor (PCA or INNSA accredited)
• ●The plan includes an insurance backed guarantee of at least five years (some lenders require ten)
• ●The Knotweed is being actively treated, not just monitored

Without these in place, most lenders refuse the mortgage outright or attach significant retention conditions. A specialist or cash buyer may still proceed, but the buyer pool shrinks significantly.

There are three main treatment approaches:

• ●Herbicide treatment over three to five years, with annual visits and a final dig. Typical cost £2,500 to £6,000 with a ten year insurance backed guarantee.
• ●Excavation and removal, where the affected soil is dug out and removed to a licensed landfill. Faster (one to two weeks) but expensive: £15,000 to £40,000.
• ●Cell burial or root barrier, where the Knotweed is buried on site with a root membrane. Mid range cost: £8,000 to £15,000.

For most sellers, herbicide treatment with an insurance backed guarantee is the cost effective answer and meets all mainstream lender requirements.

If you have a management plan, attach it to the TA6 response when your conveyancer sends it to the buyer's solicitor. Include:

• ●Date Knotweed was first identified
• ●Name of treatment contractor
• ●Plan details and ongoing visit schedule
• ●Insurance backed guarantee certificate
• ●Any planned dig out date

A buyer with this information up front is far more likely to proceed than one who only finds out via the survey.

Studies by RICS and the Property Care Association suggest a typical value impact of five to ten percent for a property with active Knotweed, falling to one to three percent once a treatment plan is in place. The biggest discount applies where the seller has done nothing. A seller with an active, insured treatment plan loses far less value than a seller who tries to hide it.

Buyer's surveyors are trained to spot Knotweed. The RICS HomeBuyer Report (Level 2) and Building Survey (Level 3) both include Knotweed inspection. If your buyer's surveyor identifies Knotweed and you have not disclosed it, the sale will almost certainly fall through.

The 2023 Davies v Bridgend County Borough Council case clarified that landowners can claim damages for Knotweed encroachment from neighbouring land for a longer period than previously assumed. This makes disclosure more important than ever, because failure to disclose can have legal consequences extending years past the sale.

If you are selling a property with known Knotweed, instruct your conveyancer the day you list. We can recommend specialist Knotweed contractors with insurance backed guarantees that are accepted by all mainstream lenders, and structure the disclosure documents so the sale is not derailed by surprise findings later.