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  1.  
    Swiftly reaching the limits of my knowledge when it comes to drainage, I have realised. The layout below is what we currently propose but I'd be grateful for any input/critique and experience of what to look out for

    I'm intending to avoid soil stacks going through the roof and want to do the lot with stub stacks and AAV's where required - this should be possible since we have a bungalow arrangement.

    Looking at the levels, there'll be several items (bath and MVHR condensate drain) which will need to enter the main stack at a lower level than the main WC pipe (float?). I understand that certain manufacturers offer a collar boss arrangement that is designed to allow this without needing the standard 200mm separation to avoid backflow.

    This is appealing, since we only have 50mm screed, then RC slab on insulation so I'm keen to keep as much of the horizontal runs above the FFL as possible. However I realise there may be horror stories with this so please share any ideas.

    Likewise, draining the island unit dishwasher and sink is a challenge. What I've ultimately come up with is a separate run below slab, meeting in the nearest inspection chamber so everything can be rodded.

    In terms of sizing, I've assumed 40mm pipe to everything but the WC's. 110mm stacks and whatever we need below ground. This is mainly to keep things 'simple' rather than mixing 32 and 40mm pipe but again if this is overkill it would be good to know.

    Any opinions on solvent vs. push-fit?

    Thanks in advance.
  2.  
    Jpeg below for anyone who can't open the link
      AboveGroundDrainage3.jpg
    •  
      CommentAuthordjh
    • CommentTimeAug 16th 2017
     
    I'm not an expert either. That's one reason I used a water board-approved plumber, as well as to avoid an extra inspection. So I have questions as much as advice.

    (1) I don't think you'll need AAVs on the sinks in the kitchen, but check with your plumber.

    (2) I think the AAVs on the soil stacks need to be 110 mm units. Are they?

    (3) Note that the 'WC manifold' will be somewhat lower by the time it gets to the second WC, reducing the height available for extra connections to the stack below the WC connection. Check carefully how it will all fit together - I ended up with the waste pipe from one WC on the first floor passing above floor level in my plant room since there wasn't space to put it in the floor void. Not a disaster but not very elegant either!

    (4) Where is your vent pipe? Mine is a 3" steel rainwater pipe up the outside of the house.
  3.  
    Djh, thanks for the swift response.

    We definitely intend to use an approved plumber nearer the time, but I realised the number of above ground drops etc. will affect the below ground runs and therefore the number of penetrations through our slab - so it's yet another decision that we need to do earlier than I'd assumed because the slab is due to start fairly soon.

    To answer in order:

    1. I saw some fairly complex (loop vent?) plumbing arrangements for kitchen islands generally, so thought it best to allow for something here. Will check with the plumber once they're on board though.

    2. Yes, the soil stacks are planned as 110 units. They'll probably need to be capped with a valve rated to sit below the 'basin flood level' as I'm hoping to conceal them within a vanity unit (or kitchen unit)

    3. Noted. The multi-pipe collar boss ('8-way soil manifold) that I was looking at appears to allow for this with an adjustable bend for WC's so the hole remains consistent despite the fall on the pipe. I've attached an elevation of the current strategy but again this all needs checking with someone who knows their waste pipes.

    4. As above, it's all single storey so I'm counting on being able to use a durgo valve instead of a standard SVP.
      Elevation.JPG
    • CommentAuthortony
    • CommentTimeAug 16th 2017
     
    You may be able to get away with HepVO trap as an air admittance valve.

    I would have an external vent pipe at the head of the run

    I would run the kitchen sink shower and bath all to the same external gulley

    I would run the two WC's on a good fall pipe into an external vent pipe collecting sinks and basins on the way

    No drains under building, one pipe in screed to island sink
    •  
      CommentAuthordjh
    • CommentTimeAug 16th 2017
     
    Posted By: Doubting_ThomasI'm counting on being able to use a durgo valve instead of a standard SVP.

    I think it's your BCO that gets to make the decision as to whether you have one or not.
  4.  
    Thanks guys,

    I've asked our BCO about the vent pipe at the head of the run and the durgo valve / HepVo etc.

    Tony, are you suggesting a single external gulley 'pot' that receives separate pipes out from kitchen sink, bath etc.? That sounds like a lot more holes in the outside wall. I was hoping to just use the inspection chamber from the drain as a rodding point, so I can't see what advantages the gulley brings.

    Agree on avoiding the drains under buildings, but we only have 50mm screed + 10mm (?) finish. Even with 32mm pipe that's not a lot of cover. Do you think it's doable or would the screed just crack?
    • CommentAuthortony
    • CommentTimeAug 17th 2017
     
    Chase pipe a bit into the concrete need 50mm screed minoften 65mm now

    Can't run sink and/or shower straight into a drain in my book
    •  
      CommentAuthordjh
    • CommentTimeAug 17th 2017
     
    My kitchen sink and my downstairs shower run straight into separate drains; I don't see what the problem is and neither did my plumber or BCO. I don't have any waste pipes through my walls at all; they all go under the slab.
  5.  
    Posted By: tonyChase pipe a bit into the concrete need 50mm screed minoften 65mm now

    Can't run sink and/or shower straight into a drain in my book


    Our S/E says we can't reduce the slab at all (it's a raft) so can't channel out below screed. Sinks will all have p-traps or bottle traps and run to a stub stack which sits over a drain (just as in the main stack to the bathroom).

    Shower is intended to be walk-in wet room type, with a 'bottom outlet' gulley (plus bell trap) embedded in the slab - like a commercial kitchen. Outlet from gulley drops straight down to drain below. I can see how this might need to be vented as there's no stack to this branch, but will wait to see what BCO says.
    •  
      CommentAuthordjh
    • CommentTimeAug 18th 2017
     
    Posted By: Doubting_ThomasShower is intended to be walk-in wet room type, with a 'bottom outlet' gulley (plus bell trap) embedded in the slab - like a commercial kitchen. Outlet from gulley drops straight down to drain below. I can see how this might need to be vented as there's no stack to this branch, but will wait to see what BCO says.

    My downstairs shower is also a wet room with the gulley/trap let into the slab, which is also a raft. We had reduced the depth of the slab in the area to make room for the trap but I still had to chisel out some more in the precise few square inches (after checking with the SE) because the depth wasn't quite enough.

    I went for a side outlet because I wasn't confident that the vertical 110 mm waste pipe stub would be precisely under the waste position in the shower base former. The trap outlet is led by a short length of 40 mm pipe straight onto the top of the piece of 110 mm poking out of the slab. There's no need for a vent.
    • CommentAuthorMarkyP
    • CommentTimeAug 18th 2017
     
    would a 20mm chase really undermine the slab integrity? My slab is 150mm mesh reinforced concrete, I'd not even have bothered asking the SE had I need to run a small chase through that to drop a pipe 20mm in.

    Can you re-inforce the screed over the pipe? Some EML or EWI type mesh?

    Does a crack even matter? What's the finished floor covering.

    personally I'd chase in 20mm and mesh the screed.
    •  
      CommentAuthordjh
    • CommentTimeAug 18th 2017
     
    Again though, why risk it when Tom's original plan appears fine?
    • CommentAuthorMarkyP
    • CommentTimeAug 18th 2017
     
    I'd prefer not to run under the slab.
    •  
      CommentAuthordjh
    • CommentTimeAug 18th 2017
     
    Why not run under the slab?
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