Japanese knotweed
Plant material the surveyor thinks may be knotweed is in the inspection chamber. Why is that a specialist identification, not a drain rating?
Because the plant material in the inspection chamber still needs identification, it is a specialist question and not a drain rating. The surveyor thinks it may be knotweed. 'May be' is not a confirmed name, and it is not a grade for the drain. A drain rating, if the survey uses one, describes the drainage that was seen. It does not identify a plant. GOV.UK's knotweed guidance is about not spreading the plant. Pulling the material out to look does not belong in the survey.
Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.
What is the fuller explanation?
Chambers sometimes hold roots, silt and debris. Naming a root from a torch at arm's length is exactly the sort of guess the report should refuse. The honest line is that material is present and that it may be knotweed, so someone who can identify it should look. That specialist step is not a CCTV grade and not a condition mark dressed up as botany. RICS knotweed guidance is about the plant and property, not about turning a chamber note into a pipe rating.
Leave the material in place rather than raking it onto the garden, which is how plants get spread. Tell the solicitor and, if the survey reports knotweed as a possibility, tell the lender that the identification is outstanding. Do not invent a treatment distance from the chamber to the house. Ask a specialist to identify what is there. Until they do, you have a materials question in a chamber, not a finished drain rating.
What should you ask your surveyor?
- Did you record the material as possibly knotweed, not as a named drain defect?
- What did you actually see in the chamber, as against what a specialist must identify?
- Is any drain comment kept separate from the plant identification?
What are the typical next steps?
- Treat the chamber material as needing specialist identification.
- Do not convert that material into a drain rating.
- Do not pull it out and spread it while you wait.
Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.
Also asked about this
If the chamber water runs, is the plant irrelevant?
No. Running water is a drain observation. It does not identify the plant, and it does not turn 'may be knotweed' into a rating.
Can the surveyor bag a sample as the identification?
No. Bagging a sample is not the home survey, and it risks spreading the plant. Identification of what is in the chamber belongs with a specialist.