Soil pipe across wall

10 Mar 2023
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United Kingdom
Hi, we currently have a vertical soil vent pipe. It is in the way of where we would like to build a rear extension. I’m hoping someone could offer some guidance here as without moving this pipe we’d be unable to open up the rear of the house.

Is it likely to be acceptable to remove the bottom portion of the SVP (crossed out in red), then route it horizontally across the wall (with the correct fall angle of course), round the corner of the wall to the side of the house and then back down vertically to join a new underground pipe?

Thank you.


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Rethink that.
If nothing is draining into that stack pipe above the toilet then what you are really doing is installing a new soil stack round the corner, the loo then becomes a long branch into the stack.
Have a look at Approved Document H
I'm not sure if this changes anything, but there is another bathroom above that one which also drains the toilet/shower/sink into that same stack?
Not regs wise. Better to have another long branch into a vertical stack, you could run into problems with solids hitting an elbow after a significant drop (look at rest bends).
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Is it feasible to take the branch runs horizontally from the pans inside the building, to emerge on the side wall, to connect into the new stack position?
I’m really hoping to avoid taking the pipes out sideways as it would involve a lot of work in the fairly new bathrooms on the 1st and loft floor.

Perhaps it is better to have the extension less open plan and leave the soil pipes where they are? That would mean they enter the ground inside the extension - would that be acceptable?

I’m guessing the rain water pipes are much easier to divert and we can take them pretty much where we like?

I’ve attached another photo that more fully shows the pipe work up to the loft level.
Thank you.


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That pipework looks fairly horrific - thrown in rather than planned.
The stack appears to be non-compliant (venting too near an opening)
Yes you can have the stack pipe inside, though you may encounter problems with noise, any leaks will be very disruptive to find and repair and you'll almost certainly need an indoor manhole for rodding access.
Rainwater pipes- depending on your local policies, you may be required to include a soakaway to handle rainwater from the new extension.
Stack internally is not an issue, box it in, ideally in a corner and you'll hardly notice it. Drain is fine under the building provided it's suitably protected with concrete depending on depth. Ideally needs to connect to the main sewer inside a chamber if it doesn't already so it's accessible if required.
Yes it does look terrible doesn’t it!

Currently there is a manhole in the patio outside this wall which would be covered by the new extension floor.
I understand that internal manholes can be an issue?

We are however at the start of a drain run so the part that all these pipes lead to is a private drain. Does that allow more flexibility with the rules?
Private Drain is yours, so can pretty much do what you like with it within the rules. If it's shared, then you need Water Company's permission to do anything as it's their asset.

Internal chambers are not ideal, if there is an issue, it's not the easiest to jobs to unblock or repair inside the property.... If the lot can be rerouted to an outside position then that would be preferable.
As @Hugh Jaleak , private drain so only building regs to worry about.
Internal manholes, if theres no other way out then they are doable but much better avoided.
I do wonder if you're overthinking this. The best, easiest (as far as i can see) option is new stackpipe round the side and new branches from the loos and other nonsense. Depending on the height of your proposed extension you might come unstuck with the lower branch (fall too near the roof).

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