I want to move my kitchen (ground floor). I need some advice on what I can do to connect the sink and dishwasher (no washing machine) to the existing drain. The direct path crosses another room and a dorway - so it can't go above floor level. I've done some reading, but not found anything exactly right. The floor is wood with a void under it. There is an inspection chamber through the outside wall about 7/8 meters from where I plan to fit the sink. Is it OK to put a trap under the sink - same as the one that would be used if I connected this a branch directly to vertical stack - and run the waste pipe under the floor, with the right fall, straight through the wall of the inspection chamber? If not what can I do instead? If yes, what is the right pipe size for this? Is 40mm OK, or do I need to go to 50mm? What is the right fall? For that run do I need an AAV? If so what height does that have to go at? Can I fit it under the worktop? If not, could it go behind a built-in fridge about 2m closer to the inspection chamber than the sink? Would an anti-syphon trap be OK? Thanks
Yes you can run a drain under a floor providing you can support it well and run it at the correct gradient to connect to the manhole / inspection chamber outside. You may prefer to connect the 50mm waste pipe to a 100mm stub stack outside then connect the 100mm stub stack direct to the manhole Waste pipe size 50mm gradient idealy 1 in 40 / 1 in 60 max AAV to be installed above spillover level of top of sink Hope that helps
Thanks Shadow - sounds like I'm on the right track. Can you point me at a picture of what you mean by a stub stack? I've done a picture of what I described. If I take the 50mm straight into the inspection chamber are there rules about how far it has to end below the top of the chamber, or above the pipe that flows through the chamber. How far does the 50mm pipe have to go through the chamber wall? There is no problem hiding the AAV behind a built-in fridge? Thanks Simon
In theory yes you can run the drain line as shown on your plan, providing you have enough depth under the floor to connect to the inspection chamber. You will need a minimum of 160mm fall in the pipework plus 50mm pipe = 210mm total void under the floor. A stub stack is just a short vertical length of drain with either 100mm or 50mm connections to take soil or waste pipes and usually capped off or fitted with an AAV.
You need to get hold of a Polypipe soil and waste and drain pipe brocure. Soil and waste pipe fittings are white grey or black Below ground drain pipe and fittings are brown You can down load from Polypipe via the web
Or pop into Screwfix or Toolstation a get a catalogue you will also be able to get fixed up with materials from there. One very important thing to mention I am guessing that the new drain will be exiting your house below ground you will need to seal the pipe to stop ingress of any ground water or surface water back into the house. Best also to consult with Building Control for any approvals you may need. If your not confident of undertaking the work yourself it may be better to get a contractor involved.
Thanks Shadow I'm going to have a builder do it. One who quoted said it couldn't be done that way, and wanted to put in a new gully on the left of the diagram with a trench 20+m long to another existing drain. The others didn't seem to know what to do. I think I can now suggest a cost effective way forward. Thanks again
Your welcome, glad gto hear you got a builder involved. As long as you have a deep enough void below your floor that you can gain access to install the pipework at the gradients i gave you and providing that the invert level on your inspection chamber is deep enough you should be able to do it. i have just done a similar job where i connected a new internal drain to an inspection chamber.
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