Selling a House with Japanese Knotweed: Facts, Costs and Options

The current position (RICS 2022 guidance onwards)

The property industry's approach to Japanese knotweed has softened significantly. The RICS 2022 assessment framework replaced the old blanket "within 7m" rule with a risk-graded system:

• Management Category A — small infestation, no damage to property, no risk of encroachment. Impact on value is often nil to minor.
• Category B — knotweed within 3m of a habitable structure; treatment or management plan required.
• Category C — knotweed causing or likely to cause damage; excavation may be needed.
• Category D — active or historic damage; specialist advice essential.

Most mainstream UK mortgage lenders now accept a professional management plan with a 10-year insurance-backed guarantee (IBG) as sufficient to lend against.

Treatment costs (2026)

| Approach | Typical cost | Timeframe | | --- | --- | --- | | Herbicide programme (3–5 years) | £2,500 – £5,000 | 3–5 seasons | | Excavation and removal | £8,000 – £25,000 | 1–4 weeks | | Root barrier installation | £3,000 – £7,000 | 1 week | | PCA-certified survey and plan | £250 – £600 | 1–2 weeks |

Only firms accredited by the Property Care Association (PCA) or Invasive Non-Native Specialists Association (INNSA) can issue an IBG that lenders will accept.

The seller's disclosure obligation

The TA6 Property Information Form asks directly whether the property is affected by Japanese knotweed. Answering "No" when you know otherwise is misrepresentation and buyers have successfully sued for the difference in value plus treatment costs (see Downing v Henderson, 2023).

Answer honestly — "Yes, currently under active PCA-managed treatment with IBG" is a fully sellable position.

What the market actually pays

Where a valid management plan and IBG are in place, RICS Cat B properties typically sell at a 3–8% discount vs comparables — sometimes less in strong markets. Untreated infestations, or homes where excavation is needed to unlock a mortgage, can see 15–25% discounts on the open market or become mortgage-unaffordable altogether.

When a cash sale is the right answer

• You need to sell before treatment can be completed
• The infestation has caused structural damage
• The garden is shared with a knotweed-affected neighbour
• Previous listings have fallen through at survey stage
• You cannot afford £10k+ excavation as a seller

Cash buyers don't need lender approval, an IBG, or a completed treatment programme. Quick Sales UK will still ask for a PCA survey to price the offer honestly, but the sale itself proceeds regardless.