I paid Thames Water for "an asset location search" and no public assets were identified on my property by their maps. If I keep access to the manhole, and ensure the sewer pipe isn't damaged by the extension, am I still obliged to pay to get agreement from Thames Water, and am I bound by its rules regarding how close I can lay foundations to a manhole?
Answer: Yes. Some minor public sewers that serve several houses often run along the rear of older properties and do not always appear on maps.
A sewer is a pipe that serves more than one property and if that pipe connects to the drainage network of the water authority, then it is a public sewer.
There seems to be a public sewer on your property as the sewer pipe certainly serves your neighbour and may also serve other properties in the terrace.
You must apply for a "building-over agreement" from the water authority to ensure the works will not cause the drain to collapse and will not prevent the water authority accessing the sewer for repair and maintenance. Don't forget Building Regulation and Planning Consent.
You may be able to build over or you may be required to divert the sewer, which would be at your expense. It may be easier to amend your plans so that the extension is further than three metres from the sewer.
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Fiona is a partner in the residential real estate team at Thring LLP (www.thrings.com).
These answers can only be a very brief commentary on the issues raised and should not be relied on as legal advice. No liability is accepted for such reliance. If you have similar issues, you should obtain advice from a solicitor.