Plumbing a kitchen island unit

[DaveH]

Trying to get my head around exactly how I should run the plumbing for a sink and dishwasher to an island before I lay the insulation, UFH and screed on the concrete slab. I will run hot and cold feeds in plastic pipe inside separate ducting along with an electrical feed for sockets. Can anyone advise on the drainage side of things please? There will be a run of approx 2.2m to an external wall and I'm thinking the best route would be straight through this wall to the side of the house as the main drain runs here, although not at great depth at this point (under a footpath). The main soil stack will be upstream from where the sink drain will emerge. What is the minimum height above the main drain that this sink drain should be? Also, I'm guessing I'll need to factor in a vent pipe or air admittance valve somewhere? Inside the island unit or run an additional pipe back to the wall (to be hidden behind wall mounted units)?

 

Thanks in advance

[PeterW]

Did similar however there are a few things to bear in mind. 

 

Run it in 50mm if possible, 40mm is the minimum if you are burying in concrete. 

 

Where the pipe drops into the slab, use a tee and run the leg a bit further back, 45 degree bend and then put a screw cap on where it comes out of the floor under the island - you’ll be able to run thin rods through this if it ever blocks. 

 

 

[Nickfromwales]

Hi dave. 

Deffo run a 110mm soil pipe to the foul network outside ( NOT the rainwater ) and reduce to 50mm after the 110mm rises above the slab. 

As it’s a kitchen sink not a bath / other I’d avoid running anything smaller bore tbh. You could go for 50mm but then you have to have the reduction done underground outside which isn’t great. 

When the 110mm rest bend turns to vertical your pipe will be pointing up out of the slab. Get a 110mm x 50mm reducer and take that immediately into a 50mm Y branch ( T ). Into the 45/d off spur of the branch you put the sink etc and the vertical 50mm outlet of the branch goes to a rodding eye for access. 

I’ll do a pic in a mo.   

[Gav_P]

24 minutes ago, Nickfromwales said:

Hi dave. 

Deffo run a 110mm soil pipe to the foul network outside ( NOT the rainwater ) and reduce to 50mm after the 110mm rises above the slab. 

As it’s a kitchen sink not a bath / other I’d avoid running anything smaller bore tbh. You could go for 50mm but then you have to have the reduction done underground outside which isn’t great. 

When the 110mm rest bend turns to vertical your pipe will be pointing up out of the slab. Get a 110mm x 50mm reducer and take that immediately into a 50mm Y branch ( T ). Into the 45/d off spur of the branch you put the sink etc and the vertical 50mm outlet of the branch goes to a rodding eye for access. 

I’ll do a pic in a mo.   

That’s exactly what I did. ?

[DaveH]

Thanks. My slab is already in without pipes or ducting. Is the attached diagram OK?

sink drainage.pdf

[PeterW]

You can’t drop from a 50 straight into a 110 underground. Needs something like a bottle trap with a back inlet and a Y branch into the main drain otherwise you will her smell issues if it all dries out. 

[DaveH]

Thanks Peter. Obviously there will be a bottle or P trap under the sink but you mean underground too? If I put a Y branch into the foul drain, 

 

 

then a P trap,

 

 

 

and finally a reducer 

 

 

will that be OK to drop the 50mm pipe into underground?

 

[PeterW]

Prefer using stuff like back inlet gullies 

 

Back Inlet gully

 

Allows you to rod if needed and also empty buckets etc 

[DaveH]

2 minutes ago, PeterW said:

Prefer using stuff like back inlet gullies 

 

Back Inlet gully

 

Allows you to rod if needed and also empty buckets etc 

 

OK. So the 50mm to 110mm reducer would go onto the back of the gully and then it would connect into the Y branch and feed into the drain? Ability for rodding is always a plus!

[PeterW]

Yep spot on.. 

[DaveH]

Should I just fit an air admittance valve into the pipework inside the island unit or am I better running a separate vent pipe back under the insulation too? I'm guessing an air admittance valve will be fine but I don't want to find out after I've laid the UFH and screed that something else needs to be in there!

 

One last question (I hope).

 

[Nickfromwales]

16 hours ago, PeterW said:

You can’t drop from a 50 straight into a 110 underground. Needs something like a bottle trap with a back inlet and a Y branch into the main drain otherwise you will her smell issues if it all dries out. 

Disagree, sorry.

There is a trap on every bathroom connected to a FW 110mm, which solely rely on the water in the trap for staving off back-stench from the sewer.

 

You simply have a rest bend coming up from the slab, reduce to 50mm, and then connect to an appropriate trap. You won't get smells from the sewer unless you stop using the sink.

2 hours ago, DaveH said:

Should I just fit an air admittance valve into the pipework inside the island unit or am I better running a separate vent pipe back under the insulation too? I'm guessing an air admittance valve will be fine but I don't want to find out after I've laid the UFH and screed that something else needs to be in there!

As a) the invert from ground floor sink to horizontal FW 110mm pipe is less than 1300mm and b) you'll only ever be discharging a sink full of water through a waste outlet ( low litres per min flow / velocity ), you'll never get a vacuum deficit and therefore do not need an AAV. The image above is USA I think? Way OTT  

[Nickfromwales]

 

If you fit one of these youd better get Dynorod on speed dial ! This will block with food waste in about 2 weeks. Thats for clear running / rainwater only. 

[PeterW]

1 hour ago, Nickfromwales said:

You simply have a rest bend coming up from the slab, reduce to 50mm, and then connect to an appropriate trap. You won't get smells from the sewer unless you stop using the sink.

 

How do you plan to rod that then if it blocks....?

[Nickfromwales]

18 minutes ago, PeterW said:

 

How do you plan to rod that then if it blocks....?

Read it and weep woody. 

50mm branch with a rodding eye inside, and as it would connect to an appropriate IC outside you’re covered both ends.

Have I taught you nothing ? ?