Buying a property with Japanese knotweed is a manageable process once you know the four steps that matter: survey, plan, guarantee and price. Knotweed is common enough that lenders and conveyancers have a settled way of dealing with it, so a stand need not derail a purchase. Our guide to how knotweed affects a mortgage explains the lender's side, and this page walks through what a buyer should do from the moment knotweed is disclosed or found.
What should you do when buying a property with knotweed?
When buying a property with knotweed, the practical steps are to have the stand surveyed, obtain or require a professional treatment plan, ensure there is an insurance-backed guarantee the lender accepts, and reflect the position in the price. These four steps turn an alarming disclosure into a costed, managed factor. Most purchases affected by knotweed complete on exactly this basis, with treatment continuing after completion under the plan and guarantee, so the transaction proceeds while the plant is dealt with over the seasons.
Do you need a survey before buying?
A survey is strongly advisable before buying, because it confirms the species, maps the extent, assigns the RICS management category and produces a costed plan, which is the evidence both you and your lender rely on. A mortgage valuer will flag knotweed but will not usually map it in detail, so a specialist survey fills that gap. Where a stand is close to the house or the boundary, the survey is what tells you whether it is a minor factor or a significant one, and it gives you a figure to negotiate with.
Who arranges the treatment plan and guarantee?
Either the seller arranges the treatment plan and guarantee before completion, or you negotiate a price reduction and arrange it yourself afterwards, and both routes are common. What the lender wants is a plan from an accredited firm and a guarantee in place, not necessarily the treatment finished. A Property Care Association member issues the guarantee, typically for 10 years. Agreeing early who arranges the treatment avoids a late hold-up, and a survey with a costed plan gives both sides the figures to settle it.
How do you negotiate the price?
You negotiate the price using the cost of dealing with the knotweed as the basis, so where the seller has no plan in place, the likely cost of treatment or excavation is a fair deduction from your offer. A herbicide programme runs from around GBP 1,500 to GBP 3,500 and excavation from around GBP 5,000 upwards, indicative and confirmed at survey. Where a plan and guarantee already exist, the discount is smaller because the risk is managed. Establishing the cost first is what makes the negotiation evidence-based rather than a guess.
Common questions
- Can I pull out if knotweed is found after my offer?
- Until contracts exchange you can usually withdraw or renegotiate, so knotweed found during conveyancing is often a point to renegotiate the price rather than to walk away. A survey gives you the cost to base that on.
- Does knotweed have to be declared to me as the buyer?
- The seller must answer TA6 question 7.8 honestly, disclosing whether the property is or has been affected by knotweed. A false answer can found a misrepresentation claim, but you should still survey to confirm the position.
- How long will treatment take after I buy?
- A herbicide programme runs across 3 to 5 seasons and continues after completion under the plan and guarantee, while excavation clears a stand in days. The method and timescale are set out in the management plan.