New drain layout questions

30 Dec 2008
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United Kingdom
I'm building a single storey extension and currently the drains are right where the extension is going so I need to make some adjustments. Currently there is a soil vent pipe connected to the uptairs loo and a gully for the kitchen sink, appliances, bath and basin (upstairs)

I want to remove the manhole from where the extension will be. The simplest option seems to be to box in the SVP (which will be in the new kitchen), remove the gully, then add a sub stack in the new downstairs loo which will also take the utility waste.

Hopefully this explains it:

Is there a better option? I'm not massively keen of having the SVP in the kitchen. I could move the SVP to the downstairs loo, but seems like more work for minimal gain and will reduce the door opening.

Can I run bath and basin waste from the upstairs bathroom into the new downstairs loo sub stack via the utility room directly below or is this too far to go with 40mm?

Can I hook the new kitchen sink waste into the existing pipe as shown? It needs to drop about 700mm in quite a short space, is there some kind of bottom exit gully?
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If the existing stack is cast iron, I would replace before hiding it inside the building. If it was to start leaking at a later date inside you'll be demolishing half the kitchen to get at it..... Replace with plastic, then bath and basin wastes can be connected internally at 1st floor level.

Utility room/ground floor W.C. drain, appreciate you're showing a chamber outside, but i'd strongly suggest you fit another chamber where this new run is joining the existing drain. The current run is accessible from the existing chamber, but if you do away with the existing chamber then you are leaving the run unaccessible in the event of a blockage!

Suitable gulley can be provided for kitchen waste pipe(s), use necessary bends to connect, if you fit a new chamber nearby then i'd just connect into that.
Thanks Hugh, that makes sense. The only bit that is confusing me is when you say that the bath and basin can be connected internally. The waste comes out of the toilet about 6 inches above the floor and the bath waste is below the floor.

This is the current layout
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Existing stack is plastic so should be ok to leave in situ. :) I'd look at coupling the bath and basin wastes into the stack with a boss as the (I assume) shower waste does at present. If new extension has a pitched roof, depending on where that meets the existing external wall, may give you enough space to hide the wastes within the roof space.

If connection into the utility room stub stack is necessary then upgrade to 50mm waste.

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