Drainage and septic tanks
The extension appears to stand over the line of a public sewer on the plan. What build-over consent has the survey not produced?
The survey has not produced any build-over consent. The extension appears to stand over the line of a public sewer on the plan, which is a reason to ask whether a water company agreed the build. An agreement of that sort is a document. The inspection can note the apparent overlap. It has not applied for consent, has not found a letter of consent, and has not decided that the sewer is, or is not, under the foundations.
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?
Plans of public sewers are lines, and an extension footprint is another line. Where they seem to cross, build-over consent is the water company's question, often with building control alongside. A surveyor comparing those lines has not opened the ground and has not read the company's file. Appearance on a plan is not a consent, and it is not proof of the exact depth or route. The report should keep the wording at apparent overlap.
Ask the solicitor for any build-over agreement, and if none is in the pack, for enquiries of the water company. Keep the survey sentence as the flag, not as the permission. Do not tell a lender the extension was approved over the sewer because a plan was glanced at. The home survey has not produced that consent and cannot be attached as if it had.
What should you ask your surveyor?
- What build-over consent, if any, did you have in the papers?
- How far did you take the apparent overlap of extension and sewer?
- Did you open the ground or only compare the plan?
What are the typical next steps?
- Treat the plan overlap as a question, not as consent.
- Ask the solicitor for any build-over agreement.
- Do not describe the survey as the water company's approval.
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 extension has stood for years, is consent unnecessary to mention?
Age does not produce the consent the survey does not have. An old extension can still lack a build-over agreement, or it can have one that is simply not in the survey. The inspection has not produced that paper either way. Ask the solicitor to look. Years of standing are not a document.
Can a clear manhole in the garden stand in for the agreement?
No. A clear manhole shows a chamber that was seen. It does not show whether the extension was built over the sewer with consent. The survey compared an apparent line on a plan. It has not produced a build-over consent, and a lid in the lawn is not that consent.