Waste Pipe run, diameter and length

24 Oct 2016
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United Kingdom
hi guys, im a new poster but I have used this forum for many years for tips and advice and research.
My question is, I am moving my kitchen from one side of the room to the other. Unfortunately this means my waste pipe also has to go with it, please see the photos attached, the waste will exit the house just to the lower left of the current doors.
I am planning on running it under the units (ikea, no service gap unfortunately) but I do have enough of a fall to make it to the outside wall if I use 40mm pipe.

From outside I then need to travel along the wall from left to right to meet the drain at the far side. I will be removing the step as I am planning on building decking out there as I am getting bifolds in the full length of the wall, so the deck will hopefully conceal the pipe. It looks like I have a fall to play with of around 220mm over 4.5m so that looks like a gradient fall of around 1 in 25.

I am after some advice on pipework, can I do the above in 40mm (or 75mm) pipe with AAV added? I have read conflicting articles on this.
I would really need to use 40mm in the house and then can I expand this to 75mm once it gets outside?

Any tips greatly appreciated!


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You'll need to use a minimum of 40mm for a sink waste, if putting a washing machine and dishwasher on the run as well, then go to 50mm from where the third appliance connects. Otherwise, first 3m can be 40mm, then go to 50mm. Not sure what the total length of your proposed run is, regs state max of 4m, but you may get away with slightly longer provided you upsize as required.

If ridiculously long, then consider installing a gulley or stub stack from the drain to a more convenient point to connect the waste.
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