Japanese knotweed has a fearsome reputation among buyers, lenders and sellers. Some of that is deserved: it’s a vigorous invasive plant that is hard to eradicate and can exploit weaknesses in paving, drains, boundary walls and lightweight structures. But its reputation for demolishing houses outstrips the evidence. Since 2022, RICS has taken a more measured, risk-based approach. Here’s what you need to know.
How to spot Japanese knotweed
Knotweed changes through the year, which is why it’s often missed:
- Spring: red or purple asparagus-like shoots emerge from the ground, growing fast.
- Summer: dense stands of hollow, bamboo-like canes, green with purple speckles, up to around 2–3 metres tall. Leaves are shield or heart-shaped, with a flat base, arranged in a zigzag along the stem.
- Late summer: clusters of small creamy-white flowers hang from the stems.
- Winter: the canes die back to brittle, hollow, brown stems, often still standing, with the plant alive underground.
It’s commonly confused with bindweed, dogwood, bamboo, Russian vine and Himalayan balsam. The zigzag stem and flat-based leaves are the giveaways.
What RICS changed in 2022
For years, residential surveyors and lenders worked to the “7 metre rule” from RICS’s 2012 information paper: knotweed within 7 metres of a house was treated as a serious risk. Research since then showed that approach was overly cautious.
RICS’s guidance Japanese knotweed and residential property, published in January 2022 and reissued as a professional standard in October 2022, replaced it. Surveyors now use their professional judgement to assess the risk, considering the size of the infestation, its distance from the property and whether it is causing damage, and assign a management category. The guidance recognises that where knotweed is within a property’s boundaries, the effect on value is often limited to the cost of a professional treatment plan.
What the survey will say
If a surveyor spots knotweed on or near the property during a home survey, the report will record it as a risk, describe where it is, and advise you to get a specialist assessment and a treatment plan before you exchange. The surveyor isn’t a knotweed contractor, and won’t search the whole site for it, but will report what’s visible.
Because knotweed is invisible for part of the year, a winter inspection can miss it. If a seller has had knotweed treated, or it’s in a neighbour’s garden, that’s exactly what the legal questions are for.
The seller’s legal questions
In England and Wales, sellers typically answer a Property Information Form (TA6) that asks directly whether the property is affected by Japanese knotweed, and whether there is a management plan. Sellers must answer honestly; an inaccurate answer can give the buyer a claim. If the answer is “yes” or “not known”, ask for:
- the management or treatment plan, from a specialist contractor;
- evidence of treatment carried out, and when;
- any insurance-backed guarantee, and whether it transfers to you.
Your legal responsibilities
Having knotweed on your land isn’t illegal, and there’s no legal duty to remove it. But you must not let it spread:
- the Wildlife and Countryside Act 1981 makes it an offence to cause it to grow in the wild;
- soil and plant material containing knotweed is controlled waste under the Environmental Protection Act 1990, and must go to a licensed site;
- you can face a community protection notice or a civil claim if you let it spread onto a neighbour’s land.
GOV.UK’s guidance on preventing the spread of harmful invasive plants sets out the rules, including how you can and can’t dispose of it. Don’t put it in your garden waste bin or compost heap.
Mortgages and knotweed
Many lenders will lend on a property with knotweed if there is a professional management plan, often with an insurance-backed guarantee, in place. Each lender has its own criteria, and the RICS risk category the valuer assigns feeds into their decision. Raise it with your broker early.
Should you walk away?
Usually not, if it’s been assessed and there’s a proper plan. Knotweed near a house is a manageable problem with a known cost. What matters is finding out before you exchange, getting a specialist plan and quote, and factoring the cost into the price.
A Home Survey Level 2 or Level 3 will report visible knotweed and other risks to the building and grounds. If you’re unsure which survey you need, see which level is right, or get in touch.
Sources and further reading
- Japanese knotweed and residential property — RICS professional standard (2022)
- How to stop invasive non-native plants from spreading — GOV.UK
- Homeowner advice: invasive weeds — Property Care Association