Build over and drainage package
Drainage survey, design and water company application for building over or near a sewer.
About this package
The build over and drainage package covers what you need to build an extension or other structure over or near a public sewer. It starts with a CCTV survey to confirm the route, depth and condition of the drain, moves through the technical package for the application, and finishes with liaison with the water company until the application is resolved. One fixed fee covers all three.
It suits homeowners whose rear or side extension sits over a shared drain, builders who have uncovered a sewer while setting out, and architects who need the drainage question settled alongside Building Control. Many London terraces have shared drains running behind or beneath the houses, so this is a common requirement for kitchen extensions and side return infills across the city.
The three stages depend on each other. The application relies on accurate survey information, and the water company often comes back with questions about pipe condition, access points or the foundation detail near the sewer. Handling everything together means the engineer who reviewed the survey answers those questions, avoiding the delays that can stall a project just as it reaches foundation stage.
What the package brings together
- CCTV drainage survey
- Build-over technical package
- Water company liaison
Stages
- CCTV drainage surveyA camera survey of the relevant drain runs confirms their route, depth, material and condition, and records any cracks, displaced joints or root intrusion that would need repair before building over.
- Build-over technical packageWe prepare the drawings, foundation details and supporting information for the build-over application, showing how the new structure protects the sewer and keeps the necessary access to it.
- Water company liaisonWe submit the application to the water company and answer its technical queries until it is resolved. Where conditions are attached, we explain what they mean in practice for your builder on site.
Who it suits
- Rear extensions over a shared drain
- Side return infills with a sewer along the boundary
- Builders who have found a sewer while setting out
- Projects needing a manhole moved or protected
- Architects needing drainage settled before work starts
How it works
Frequently asked questions
How close to a sewer can I build without approval?
As a general rule, building over or within about three metres of a public sewer needs the water company's approval. The exact requirements depend on the pipe size, depth and type, and on the water company's current guidance. Thames Water will confirm what applies to your sewer, and our survey establishes the facts first.
What if the CCTV survey finds a damaged pipe?
Defects such as cracks, displaced joints or roots usually need repair before the water company will agree to building over. Repairs may involve lining the pipe or replacing a section. Our drain repair specification service sets out what is needed. Fixing defects early also reduces the risk of leaks softening the ground under your new foundations.
Can a manhole be inside my extension?
Water companies generally prefer manholes to stay outside the building footprint so they remain accessible. In some cases an internal access cover with a sealed, bolted lid may be accepted, or the manhole may be relocated. The options depend on the sewer and the water company's requirements. Our guide on building over a sewer covers the choices.
Does build-over approval replace Building Control approval?
No. The water company deals with protecting its sewer, while Building Control deals with whether the extension meets the Building Regulations, including how it affects drainage. Both are needed. We send the relevant structural and drainage information to each of them, so they are working from the same details.