Guide
Build-over agreements: the drain survey your water company asks for
Updated
Extensions and conservatories regularly land on top of pipes the homeowner assumed were theirs. Since 2011 many of those pipes are public sewers, and building over one without the water company's agreement can stall a sale years later. The CCTV survey is how the agreement gets granted.
Why your garden probably contains a public sewer
In October 2011 most private sewers and lateral drains in England and Wales transferred to the water and sewerage companies (legislation.gov.uk). The practical effect for builders: the shared pipe crossing your back garden, which pre-2011 belonged to you and your neighbours, is now a public sewer with statutory protection. Building Regulations Approved Document H requires that building over or near a public sewer be agreed with the sewerage undertaker (gov.uk), and in practice water companies apply this to works over or within 3 metres of the pipe.
Where the CCTV survey comes in
- Before works: the water company typically wants a CCTV survey of the affected sewer submitted with the build-over application, proving the pipe's line, depth and condition before anything is built above it. A £150–£350 survey, sometimes with mapping (typically £50–£150 extra) where the records don't match the ground.
- Design conditions: the agreement may require lintels over the pipe, specific foundation details, or repositioned access points, cheaper to know before the footings are designed than after.
- After works: a post-construction CCTV survey demonstrating the sewer survived the build undamaged. Budget for two surveys, not one, when pricing the project.
What happens if you skip it
- Selling gets harder. Buyers' solicitors ask for build-over agreements in standard enquiries; a missing one triggers indemnity insurance negotiations, retentions or price chips, years after the builder left.
- The water company keeps its rights. A sewerage undertaker retains statutory access to its pipes; in a genuine failure it can excavate to reach a sewer, and a structure built without agreement has weaker protection when that argument starts.
- Damage becomes your problem. A sewer cracked by unagreed foundations is a dispute you are poorly positioned to win.
Application processes, fees and exact requirements differ between water companies, some offer a fast-track self-certification for minor works, so check your own company's build-over pages before commissioning anything. Ask survey firms specifically for a build-over-standard survey: the report format has to satisfy the water company, not just you.