Japanese knotweed
A rhizome crosses the benching inside a manhole. Has the drain that root has entered been camera-surveyed?
The drain has not been camera-surveyed. A rhizome crosses the benching inside a manhole, which is a root seen in the chamber, not a filmed run of the pipe it may have entered. The survey records what was visible in the open manhole. It has not mapped how far the rhizome goes and it has not tested the drain. A camera survey would be a separate instruction. This visit did not do it, so the pipe beyond the benching stays unseen.
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?
Benching is the concrete shaping in the bottom of a manhole that directs flow into the channel. A rhizome lying across it is inside the chamber. From there a root can enter a pipe, sit only on the benching, or come in from the wall. Looking down the shaft cannot show which, once the pipe bore turns out of sight. Japanese knotweed is managed as a serious invasive plant, and a fragment in a chamber is a finding. It is not a plan of the underground run.
Tell the solicitor the rhizome was in the manhole and that no camera survey was done. A drainage firm can film the pipe, and a knotweed specialist can advise on the plant. Those are two instructions, and neither is hidden inside this report. Do not tell a lender the drains are clear because the chamber was only looked at. Do not dig the rhizome out as a home experiment. Keep the finding factual until the specialists report.
What should you ask your surveyor?
- Was a camera run through the drain beyond the manhole?
- Is the rhizome finding limited to what showed on the benching?
- Has the survey mapped how far the rhizome extends?
What are the typical next steps?
- Treat the rhizome as seen in the chamber, not as a filmed drain.
- Tell the solicitor no camera survey was done on this visit.
- Instruct a drainage firm and a knotweed specialist if you need both.
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
Does a rhizome on the benching map the plant across the garden?
No. The benching shows a rhizome in that chamber only. It does not measure stands in the garden, rhizome under the lawn or growth next door. The survey did not excavate and did not set out a spread plan. Extent of the plant is a specialist question. This note is the piece that was visible in the manhole.
Was the rhizome sent to a laboratory from this visit?
No. The survey recorded a rhizome crossing the benching. It did not bag a sample or obtain a laboratory identification. A knotweed specialist can advise on identification if that is disputed. The drain the root may have entered was not camera-surveyed either. Both the plant test and the pipe film remain outside this report.