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Find answers to common home extension issues, questions you may have, planning permission and building regulations related questions.

Build over agreement with water authority for building an extension over a drain

Looking for some advice... (ignore the poor bricking up of an old door by previous owner) Want to have a single storey rear kitchen extension but I have a sewer drain cover in the middle of where I want to build over. With some limited research online you can have a (build over or bridge over) agreement. There is 2 further drain covers in a straight line (blue crosses) one just the other side of neighbours fence and one a couple meters the other side on my property.
What do I need to do to start the process? Do I need the water company out to inspect etc? What’s involved and where would you start?

Callum Ranson 26/07/2022
Building over agreement for house extension drain
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REPLIES:
BY:
Depends on who owns the drains, house deeds should tell you
James Horstead
Nope. Get the water board out to inspect. Get a build over agreement. Job done ….. just built mine over a main sewer for the whole street, no issues at all
Greg Barron
Exact situation here. Call for a drain survey and they will map everything for you. Then it will be easy for you to make a decision. Call the water company first to see if there are records of the drainage system , sometimes they have it mapped. You just move the manhole out of the area you want to build or you build over . But if you build ofer it has to be accessible somehow , so think about that as well
Alex Chirica
I've just had the same issue
We were doing a small rear extension and lifted the existing orangery floor to find 2 drains!
We got permission to move them but a considerable cost as we had to put the foundations 300mm below the drains which were 2.2m deep!
So we ended up having to knock the orangery down and build a raft 6m x 11.5m
Daniel Cannon
I've just had the same issue
We were doing a small rear extension and lifted the existing orangery floor to find 2 drains!
We got permission to move them but a considerable cost as we had to put the foundations 300mm below the drains which were 2.2m deep!
So we ended up having to knock the orangery down and build a raft 6m x 11.5m
Daniel Cannon
Just move the manhole to the other side of the red line so it would be on the outside when your digging the footings
Ross Maloney

Simple and straight answer, (1) do not start any building work (2) apply for build over or near manhole from water company (3) because of the manhole situation, get a plan for your building work with all the measurements, water company might ask for it. (4) start the building work after you receive conditional approval letter from water company. (5) get CCTV survey done (water company may ask for it for final approval letter that goes with your house). Good luck
Noah Sparks
The build over agreement will cover the pipe work your actually building over also not just the manhole I work for Severn Trent water and usually you have to have a Cctv survey to check pipework is ok ie no dropped joints or cracks water board usually inspect at certain stages of build all our work consists of putting stuff like this right when ppl have just built with no permission whatsoever and it’s a nightmare if I’m honest the last 2weeks I’ve had to replace 2 manhole covers in kitchens as they needed access which created a hell of a mess for the customer
Stuart Cole
I moved a manhole for someone once and renewed all pipework that was being built over even carried out post Cctv survey to forward to Severn Trent as they’d requested from customer he was still refused to build his extension as he was confused about drawings Severn Trent wanted a 1.2m diameter storm drain and manhole moving that was 7m deep that ran through the customers garden and they wouldn’t allow him to build within 5m of it so be very careful as they can instruct you to take it down in some instances sewers in the midlands range from 0.3m-3m deep there not all uniform depth last thing you want is having it dug up if there’s going to be problems in a few years
Josh Winters
Hi mate - our scenario was the same. Dealing with Yorkshire Water though, they wouldn’t permit a build over, and wanted a MH/IC along the alignment of the original sewer inside our boundary. Unfortunately, we had to dog leg the extension at the outflow end to cater for an IC and tie in from our stack - not ideal but it works. As for replacing existing pipe work, if you’re at it and have the plant on site, I’d definitely replace any vc pipe work with new plastic, boundary to boundary. Old vc pipes crack over time and it’s additional piece of mind to know everything under your gf slab is in good condition with better flow velocity. Good luck with the build
Severn Trent building over agreement
Arran Crawford
I built a extension for a customer with similar problem last year. It’s called a shared drain as I’m guessing your neighbours sewage goes through this and carry’s on up your street. We had to get the water/sewage company to put a camera up the drain and they then did a report on them. I hope the drain is not deep as your need to dig the footings down to the same level and your not be allowed to have your footings any nearer than 500mm. If the camera finds any faults with the pipework then it’s your responsibility to repair them at your cost. With the extension I done the shared drain was nearly 2 metres down and in the end cost them nearly 8k more.
Mark Kerry
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