kitchen island 50mm or 110mm ?

[mike42]

Hello all

Planning to extend kitchen at the back so that existing sink will be in the middle of the new kitchen on an "island". The existing sink drains outside into a gulley - that will be under the floor after the extension.

There is a small 4 inch sewer running outside the proposed extension so would it be best to bring a 110mm drain pipe to the island below the new slab? But then what? I don't plan to put in a new soil stack under the kitchen sink so what would be the normal way of connecting a 40mm or 50mm sink into a 110mm pipe down below? ANd where would the pipe get reduced - under the slab or in it ?

 

[John D v2.0]

Cut the clay pipe back underground if it's clay and connect a new 110mm pipe into it with one of those Flexi rubber connectors with jubilee clips. Then reduce the 110 to 50 and run the 50 to your island.
You don't really need 110 for a sink and dishwasher.
Ours is a similar set-up and it's been running for years with about a 5m run of 50mm to the island.
Once it's above floor level it goes down the 40mm in order to fit in the cabinet void.

 

[Hugh Jaleak]

I'd run 110mm under the floor, come upwards and reduce at or just above finished floor level.

Avoids issues with maximum waste run lengths under Part H, and is easier to clean in the event of an issue, (provide access to the run externally.)

 

[Notch7]

Hello all

Planning to extend kitchen at the back so that existing sink will be in the middle of the new kitchen on an "island". The existing sink drains outside into a gulley - that will be under the floor after the extension.

There is a small 4 inch sewer running outside the proposed extension so would it be best to bring a 110mm drain pipe to the island below the new slab? But then what? I don't plan to put in a new soil stack under the kitchen sink so what would be the normal way of connecting a 40mm or 50mm sink into a 110mm pipe down below? ANd where would the pipe get reduced - under the slab or in it ?

I used to make bespoke kitchens and often used to come across this.

I found builders would run 110mm to the island, come up with a bend and a bit of straight so the 110mm sat up In the air above the concrete slab by say 300mm. Then the floor would get insulated and screeded leaving about 100mm of the pipe exposed - then when kitchen goes in; cut down 110mm and fit reducer so they within plinth space, then take waste up through cabinet bottom in 50mm or whatever.

 

[mike42]

Thanks a lot all. Especially for the detail given by Notch and backed up by Hugh. But John's experience also interesting. All much appreciated !

 

[mike42]

Forgot to ask does it the pipe need ventilation in some way as a normal stack would be ? An aav on the 50mm upstand perhaps?
And I'd get something like this?:

https://www.travisperkins.co.uk/solvent-weld-waste-pipe/osmasoil-4s496b-solvent-weld-reducer-black-110-x-50mm/p/818080

 

[Hugh Jaleak]

Forgot to ask does it the pipe need ventilation in some way as a normal stack would be ?

Not really necessary, as the waste pipe from the sink wont be long enough to cause any issues, and by the time the water gets into the 110mm section, it'll never fill it under normal conditions, so siphonage wont be an issue.