Drainage and septic tanks
A shared drain may run under next door’s later extension. What can this survey see of that route?
Almost nothing of the length under their floor. The survey of this house can see covers on this plot, and perhaps a line of covers in the garden. It cannot inspect a pipe beneath a room the neighbour built later, and it did not camera that run unless a camera was a separate instruction.
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?
Shared drains often cross a boundary and then pass under whatever was built afterwards. The risk you are asking about is the route, not a general lecture on being a neighbour. This report cannot say the pipe is sound under their extension, and it cannot say it is broken, unless something visible on this side shows that. Roots at a chamber, a backfall, or a history of blockages are observations. They are not a film of the hidden length. A standard inspection does not remove every cover, and it never lifts the neighbour’s floor.
Your solicitor asks about rights and about any agreement that the extension was built over the pipe. The survey does not decide ownership and does not serve notices. Approved Document H does not tell you who may dig. Do not invent a transfer date to decide the pipe is public. If you need the condition of the run, a drainage firm needs access, which may mean the neighbour as well as this garden. A camera report, if you commission one, is theirs. Do not convert it into RICS ratings, and do not invent grades the firm did not use. Until then the honest line is: route not seen under the later extension.
What should you ask your surveyor?
- Which covers did you see, and which way does the run appear to leave this plot?
- Did you see the neighbour’s extension over that line, or is that only a suspicion?
- Was any camera used? If not, please say the route is unproved.
What are the typical next steps?
- Do not dig at the boundary.
- Ask the solicitor what rights exist to the shared run. Keep that separate from condition.
- If you camera the drain, include the question of access under the extension. Do not assume the neighbour must open their floor.
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 clear chamber on this side clear the pipe under their extension?
No. The chamber is one point. The length you cannot see is still unseen.
Is this the same as an extension on this house standing over a sewer?
No. Here the concern is the route under next door’s later building. Do not copy a different sentence across.