1st extension - sewer waste - help please

14 Jul 2021
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United Kingdom
I'm building an extension, and working on sewer plans. We're building over a shared drain and so BI wants new inspection chamber for rodding access.

We want a patio, so IC needs to be top right or bottom right.

Can you see any glaring problems or issues with this proposal? (shared sewer runs top to bottom)
All orange, blue pipes, including teeing into the old drain and IC will be new.

Are the angles suitable for rodding the drain or is another layout better?

Lastly the main stack is vented, will i need any other Air Admittance Valves anywhere in the system? (Sink, basin, washer will all have p traps, toilet obv built in u-bend)

Thanks in advance for your help.
2021-07-14 at 10.10.51@2x.png
Last edited:
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It looks to me like you are taking the longest route possible for your waste water.

What is below the diagram? Is it space that can be used for your pipe runs?
Is it possible to join the shared system lower down?
Both the top and bottom of the extension are right on the boundary - so can't put the IC above the existing sewer.

I interpreted the BI said I needed an inspection/rodding chamber that would mean all waste from the property needs to be through the IC that can then be rodded.

ie I'm not allowed to leave the existing waste as it is and just add a Y adapter that doesn't carry any waste but is just a rodding point.

Do you think that's correct?
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If I did something like would that be acceptable from a suitable rodding point?

2021-07-14 at 20.16.16@2x.png
Your first one won't wash. V2 and V3 aren't much better (rodding round 45 degree bends isn't fun). Your last one is about the best but how would you clear a blockage either at the shower or between the new internal stack & the clay? And think you'll need 50mm from the sink, run looks a bit long for 40. Check the Approved Docs :)

What houses are feeding into the Existing Clay Sewer. ?

Maintenance of shared sewers is the responsibility of the local water or sewage company and you need to have your plan approved by them before you start / commit to work.

Local Council building inspectors sometimes offer advice about sewer alterations without taking into account the involvement of the water or sewage company in the future maintenance of the shared sewers that are being altered.
Thanks for the feedback & suggestions - have made some edits so think this should work
Have included picture of existing sewer & proposed stack.
Blockages at the sewer Y on sewer I can rod from new chamber
Blockages from shower/basin can either be rodded from one of 2 internal access points
I'll use a sweeping bend to connect up so no tight angles anywhere.
2021-07-15 at 09.30.48@2x.png
I have attached a little screenshot from my proposal which got accepted by TW. The pink line is existing shared run


  • IMG_20210717_173130.jpg
    188.1 KB · Views: 64

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