1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

Drainage Venting

Discussion in 'Plumbing and Central Heating' started by askman, 2 Aug 2018.

  1. askman

    askman

    Joined:
    30 Aug 2017
    Messages:
    80
    Thanks Received:
    2
    Country:
    United Kingdom
    I'm doing quite an extensive renovation and just want to make sure my plan for the drainage venting is adequate.

    The house is a mid-terrace and has a flat roof extension at the back, the roof of which I don't want to touch if I can avoid it (trying to limit costs as it was done recently), hence the somewhat unconventional drainage layout. The pre-existing soil stack runs up the back of the house and currently drops down the middle of my kitchen which is not a feasible solution.

    The bathroom layout will be changing, and will have the bath under the window and the toilet in the corner furthest from the back wall. The waste from the toilet will run for approx. 1.5m in 110mm at low level along the wall with a 32mm connection from the basin and drop down internally in the corner into the below ground waste.

    The bath / shower waste will be at the opposite end of the room and as such I am proposing that it drops at 40mm through the floor in order to get an adequate fall, and connects into the vertical stack mentioned above - the run will also be approx. 1.5m.

    The boiler will be in the loft, the condense for which will drop through a 100mm boxed in section for the shower pipework and connect into the waste from the shower / bath.

    Now comes the complicated part - venting the system.

    Rather than continuing the toilet waste up and through the loft to vent to atmosphere, I'm looking to use an AAV to vent the toilet / basin float as I don't want to box in the pipe full height. The AAV will sit higher up than the basin.

    Then to fully comply with part H, the system needs somewhere for the relief of positive pressure which I'm proposing could be done by continuing the waste from the shower / bath up the boxed in section and out vertically through the loft and roof.

    If I were to do this, the boiler condense connection would be made in the loft - there is a tundish between the condense and boiler to prevent backflow.

    Would this mean that the vent pipe would need to be increased in size to 50mm?
     
  2. Sponsored Links
  3. Nige F

    Nige F

    Joined:
    28 Jun 2005
    Messages:
    20,629
    Thanks Received:
    1,611
    Country:
    United Kingdom
    I can't quite visualize your whole setup but - a tundish won't stop backflow unless you mean a Hep V O valve which can be used as a tundish AFAIK. Also condense pipework is considered part of the flue so needs a Registered Gas Installer ( which I'm not ;) ) Others here certainly are.
     
    • Thanks Thanks x 1
  4. askman

    askman

    Joined:
    30 Aug 2017
    Messages:
    80
    Thanks Received:
    2
    Country:
    United Kingdom
    93600A13-B135-4E85-BF39-9CB3F08DE204.jpeg
    Schematically it will be roughly as per the attached. I guess my main question is whether the vent can be taken from the bath / shower waste, with the toilet having an AAV or whether the AAV is needed.
    With regards to the tundish, I mean that it will prevent back flow into the boiler from the waste system.
     
  5. John D v2.0

    John D v2.0

    Joined:
    26 Aug 2016
    Messages:
    6,315
    Thanks Received:
    876
    Country:
    United Kingdom
    Vent pipe should really be 3 inch 75mm from memory of its venting 110mm pipe. See the approved document. However in reality you'll only get positive pressure in the case of rising water levels surcharging in the underground drainage system and any pipe will cope with that.
     
    • Thanks Thanks x 1
    • Like Like x 1
  6. Sponsored Links
  7. askman

    askman

    Joined:
    30 Aug 2017
    Messages:
    80
    Thanks Received:
    2
    Country:
    United Kingdom
    But in terms of layout, the above would be acceptable? I can't see any practical reason it wouldn't...
    Would the toilet / basin float need the AAV? In a standard arrangement, the toilet enters the vertical stack without a vent upstream from it so I'm concerned I may be being over-cautious. I could fit a hepvo on the basin to prevent the trap being drained if this is likely to be an issue...
     
  8. John D v2.0

    John D v2.0

    Joined:
    26 Aug 2016
    Messages:
    6,315
    Thanks Received:
    876
    Country:
    United Kingdom
    Only obvious problem is you can't easily enter the 110 and the 40 opposite each other due to cross flow. You'd have to be careful to get the 40 higher or entry on the same side.
    The other branches the diagram doesn't show any problems. You may not even need an aav on that side
     
    • Thanks Thanks x 1
  9. dilalio

    dilalio

    Joined:
    20 Mar 2009
    Messages:
    6,723
    Thanks Received:
    1,002
    Location:
    Potters Bar
    Country:
    United Kingdom
    You would need to get building control approval, so best to call them in.
     
  10. askman

    askman

    Joined:
    30 Aug 2017
    Messages:
    80
    Thanks Received:
    2
    Country:
    United Kingdom
    They won't be opposite each other, they'll be at 90degrees, I drew it as above to try to make it clearer. Point taken about avoiding cross flow though.
     
  11. DIYnot Local

    DIYnot Local

    Joined:
    3 Sep 2019
    Country:
    United Kingdom

    If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

    Select the supplier or trade you require, enter your location to begin your search.


    Are you a trade or supplier? You can create your listing free at DIYnot Local

     
Loading...

Share This Page