Selling a house with Japanese knotweed

You can sell a house with Japanese knotweed, but you must answer the knotweed question on the property information form honestly, and where the plant is damaging a structure or restricting use of the garden, buyers’ lenders will usually want a professional treatment plan backed by an insurance-backed guarantee. Cash buyers can proceed without that, but they will price the problem in.

Do I have to tell buyers about Japanese knotweed?

Yes, if you know or suspect it is there. In England and Wales, sellers complete the Law Society’s Property Information Form (TA6). In the current 6th edition, question 8.6 asks whether the property is affected by Japanese knotweed, with the answers “yes”, “no” or “not known”.

The Law Society’s explanatory notes make three points worth knowing:

a property is usually considered at risk if knotweed is growing on it or within 3 metres of its boundary
it is hard to be certain knotweed is absent, because rhizome (root) can be in the soil with no growth visible, which is why many sellers answer “not known”
if you know of a survey or a knotweed management plan, you should attach it

The notes also make the stakes clear: buyers can rely on your answers, and if you give misleading information, the buyer may be able to claim compensation after completion. Do not answer “no” unless you have a reasonable basis for it. If you are unsure, ask your solicitor.

In Scotland, the Home Report includes a property questionnaire, and your solicitor can advise on what to disclose there.

Is it illegal to have knotweed on your land?

No. GOV.UK guidance for England says you do not legally have to remove Japanese knotweed from your land unless it is causing a nuisance. You can, however, be prosecuted for causing it to spread into the wild, and soil or plant material containing it may be classified as controlled waste, with strict rules on disposal. Wales, Scotland and Northern Ireland publish their own guidance.

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How do surveyors assess knotweed now?

The Royal Institution of Chartered Surveyors (RICS) publishes a UK professional standard, Japanese knotweed and residential property. It took effect on 23 March 2022 and was reissued as a professional standard in October 2022.

It replaced the older approach, which categorised risk by whether knotweed was within 7 metres of buildings and boundaries, with four management categories based on what the knotweed is actually doing to the property.

Category	What it means	What the standard expects of lenders
A: Action	Knotweed is causing visible damage to a significant structure, such as the house, a garage or a boundary wall	Most lenders likely to require a specialist inspection and a treatment plan with an insurance-backed guarantee, subject to a retention
B: Action	Not causing damage, but likely to prevent use of or restrict access to amenity space such as lawns, paths and driveways	As for Category A
C: Manage	Not causing damage and not restricting use of the garden	Lenders ought not to require remediation as a condition of the mortgage
D: Report	Not on the property, but within 3 metres of the boundary	Reported to the lender, but lenders should not require remediation of land the owner does not control

Knotweed seen more than 3 metres beyond the boundary does not usually need to be reported to a lender.

RICS is candid about the market. The standard acknowledges that knotweed can be a significant impediment to selling, that the impact in the market is often out of all proportion to the cost of remediation, and that some properties carry a lingering stigma even after treatment.

What is a treatment plan with an insurance-backed guarantee?

A Japanese knotweed management plan is a programme of treatment set out by a remediation specialist. Depending on the site, it may involve herbicide treatment over a period of years or excavation. RICS refers to specialists who are members of a recognised trade body and to insurance-backed guarantees as typical lender requirements.

If you already have a plan in place, gather the paperwork: the survey, the plan, the treatment records and the guarantee. Check whether the guarantee can be transferred to a buyer. The Law Society notes that guarantees are often limited in time and may not be transferable.

Should I start treatment before selling?

Starting a professional treatment plan before you market the house can widen your pool of buyers, because a mortgage buyer’s lender will then have what it needs. It costs money up front, and the full programme can take time.

Whether that makes sense depends on how soon you need to sell and what the plan costs compared with the effect on offers. A remediation specialist can give you a written quote to weigh up.

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How do cash buyers approach knotweed?

Cash buyers do not need a lender’s approval, so knotweed need not stop the sale. They will, though, factor in the cost of treatment, the time it takes, and the stigma RICS describes when they come to sell on.

Offers for a house with untreated knotweed are usually well below the price of an equivalent house without it, and a quick sale generally means accepting less than full market value. Our guide to how much cash buyers pay explains how buyers work out their figures.

Disclose everything at the start. A buyer who discovers knotweed late may try to renegotiate, which our guide to gazundering explains. If you would like to see what buyers on our panel might offer, you can get offers for my home. It is free and there is no obligation to accept.

What if the knotweed is next door?

Knotweed on neighbouring land within 3 metres of your boundary falls into RICS Category D. You should still answer the TA6 question honestly and tell your solicitor what you know. RICS says lenders should not require remediation of an infestation on adjoining land as a condition of a mortgage, because it is beyond the owner’s control, and that in most cases it is likely to have a limited effect on value unless the infestation is severe.

If a neighbour’s knotweed is spreading onto your land, a solicitor can explain your options. It is worth keeping records of any correspondence, as buyers may ask about disputes with neighbours.

Common questions

Can I answer 'not known' to the knotweed question on the TA6 form?

Yes, if that is the honest answer. The Law Society's notes say many sellers answer 'not known' because rhizome can be present in the soil with no growth visible. You should not answer 'no' unless you have a reasonable basis for it, and if you know of a survey or management plan you should disclose it.

Can a buyer get a mortgage on a house with Japanese knotweed?

Often, yes. Under the RICS standard, where knotweed is causing damage or restricting use of the garden, most lenders are expected to require a specialist treatment plan with an insurance-backed guarantee, usually with part of the loan held back. Where knotweed is not causing damage or restricting use, the standard says lenders ought not to require remediation.

Do I have to remove Japanese knotweed before I sell?

There is no general legal requirement to remove it before selling. GOV.UK guidance for England says you do not have to remove it from your land unless it is causing a nuisance, but you can be prosecuted for causing it to spread into the wild. In practice, a treatment plan in place usually makes a sale easier.

What if the knotweed is in my neighbour's garden?

Knotweed within 3 metres of your boundary is usually treated as a risk to your property and should be disclosed. The RICS standard says lenders should not require you to remediate land you do not control, but buyers will still want to know about it.