At SE Knotweed, we explain that Davies v Bridgend [2024] UKSC 15 held a residual fall in value is not recoverable in nuisance where the encroachment happened before the defendant was in breach of any duty, an important limit we state plainly rather than promising a payout.
At SE Knotweed, we explain that Japanese knotweed can reduce a property's value while it is untreated, because buyers and lenders price in the cost of treatment and the perceived risk, but a completed plan and an insurance-backed guarantee usually restore most of that value.
The size of the effect depends on the RICS category, the proximity to the building and whether a plan is in place. We give an honest reading rather than a headline scare figure, and legal advice is needed for any claim over a fall in value.
Knotweed diminution in value is the fall in a property's market value attributable to the plant, made up of two parts: the cost of treating the stand, and any residual diminution, the discount that lingers after treatment because of the stigma buyers attach to a property that once had knotweed.
The distinction matters in law, because the courts treat the two very differently, as Davies v Bridgend made clear.
In Davies v Bridgend County Borough Council [2024] UKSC 15, the Supreme Court decided that a homeowner could not recover residual diminution in value from the council, because that loss had arisen before the council was in breach of any duty in nuisance, making it pure economic loss the tort does not compensate.
Knotweed had encroached from the council's land for years, but the breach only began once the council failed to treat after 2013 guidance, and the value was already affected by then. The residual diminution was therefore not caused by the breach.
You can still claim losses caused by a neighbour's breach, but Davies v Bridgend means a residual diminution that predates the breach is not recoverable, so a claim for a stigma discount on the price will usually fail where the encroachment came first.
What remains recoverable is the cost of treating the live nuisance and related expense. We state this limit plainly, because overstating a value claim sets an expectation the law will not meet.
Residual diminution is the value that stays lost even after the knotweed is treated, reflecting the discount some buyers still apply to a property with a knotweed history despite a clean survey and a guarantee.
Because Davies v Bridgend put it beyond most nuisance claims, its practical significance is now about pricing and negotiation rather than a claim. A strong treatment record and an insurance-backed guarantee are what reduce it in the market.
A commonly cited figure is roughly 5 to 15 per cent off the value while a stand is untreated, narrowing sharply once a management plan and an insurance-backed guarantee are in place, though estimates vary widely and are not fixed.
Treat any percentage as indicative, because the real figure depends on the property, the location, the RICS category and the buyer. A valuer's opinion on your specific property is the only reliable number.
Treatment and an insurance-backed guarantee restore most of a property's value, because they remove the two things that worry a buyer and lender: the unpriced cost of dealing with the stand, and the risk that it returns with no cover in place.
Once the risk is underwritten and lending can proceed, the property competes with comparable homes again. The guarantee is the instrument that carries that confidence to the market.
For any claim touching value you need a survey confirming the knotweed and its source, a costed treatment plan, and a valuer's evidence on the effect on price, alongside legal advice on what Davies v Bridgend allows in your circumstances.
We provide the survey and the treatment figure; a chartered valuer and a solicitor address the value and the law. Book a survey to establish the facts a claim or a negotiation is built on.
Tell us the address and what a surveyor flagged. We confirm the plant, record the RICS category and set out the figures.