Glossary · UK
What is Japanese Knotweed (Mortgage Risk)?
An invasive plant that can damage structures and complicate a property sale, since most mortgage lenders require evidence of a management plan or professional treatment before agreeing to lend.
Full Definition
Japanese knotweed is a fast-growing invasive plant that can cause structural damage to buildings, driveways and drains by pushing through small cracks and expanding as it grows, which is why its presence, or history, on a property is treated as a significant issue in UK residential conveyancing and mortgage lending rather than simply a gardening nuisance. A standard mortgage valuation or survey will note visible knotweed and grade the risk (commonly using a scale from the property itself to within a set distance of the boundary, such as seven metres), and most mainstream lenders will decline to lend, or require a knotweed management plan and insurance-backed guarantee from a professional treatment company, before completing a mortgage on an affected property, since an untreated infestation can reduce the property's value and, in some cases, its mortgageability. The seller's conveyancing enquiries (the TA6 property information form) specifically ask whether the seller is aware of Japanese knotweed on the property, and knowingly giving an inaccurate answer can expose the seller to a claim for misrepresentation from the buyer if the knotweed is later discovered. Treatment typically involves either an extended herbicide programme over several growing seasons or physical excavation and removal of the root system (rhizome), both usually carried out by a specialist contractor who then provides an insurance-backed guarantee that a mortgage lender can rely on, and buyers of an affected property are generally advised to obtain independent confirmation of the treatment plan and guarantee terms before proceeding, rather than relying solely on the seller's assurance that the problem has been dealt with.