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Discuss Will I need a Durgo/ AAV or indoor ventilating stack? in the Plumbing Forum area at

  1. 1justin

    1justin New Member

    Planning a small installation with Part H to hand, (building control app'n is granted) and just want some confirmation here that I'm getting this right for building control. The drainage is the only main inspection BC need to make (Since I'm part P electrician).
    WC, low level shower, basin, 1970's uninsulated concrete ground floor.

    Existing manhole (approx 1M invert), will be accessed with a new 110mm pipe dug through the wall/foundation. Existing manhole is about 2.5 M away from the proposed vertical WC outlet
    I want to keep this as simple as possible, ideally without boxing for pipes, - but it seems to me that I really can't escape the need for a ventilated stack with a durgo alongside the WC.

    Bear with me. I envisage a stack (to be boxed in) with 100mm durgo on top (stack height is TBD). Branch 100 mm waste to WC (~ 500mm long) just above floor level, and somewhat further up same stack (>=200mm offset) would be 32mm waste from basin, to be run along the wall.
    The low level shower tray means a 40mm waste (from 90 dia low profile trap) and this must be dug into the floor (ie displacing screed and potentially also some concrete, & if I find the DPM between the two that's to be dealt with)
    The 40mm shower must branch into the stack below the floor level. I'm thinking the only way to do this is (diagram 2 in part H) to use a 50mm parallel junction alongside the stack, to get the joint 200mm below the wc waste).
    I'd make all inaccessible joints in solvent weld and test before back filling.

    Am I on the right lines here, and if so how high must the 110mm stack go alongside the WC? (Will be boxed in alongside the WC, with durgo atop).

    (I'm sure the aesthetic would be much nicer if I can make all drainage disappear like magic into the floor, but I can't see any way to achieve that. )
  2. Vee

    Vee Plumber GSR

    AAV (Durgo) needs to ventilated ( to be able to work effectively) and accessible as per Part H. My pet hate is boxed in AAV on a stub. It can't breathe. When (not if) it fails and the bathroom stinks, you need to rip the bathroom apart to fix it. Accessible meaning access hatch sufficient to change if faulty. AAV best in loft if you don't want to take it outside. There should be at least one vent to outside from the drainage system.
    • Like Like x 1
  3. 1justin

    1justin New Member

    Thanks Vee. Yes I had no intention of building one in without access. Turns out now that I have discovered external AAV exists, I'll run an external stack instead. Building Control (I asked them) seem to be OK about external AAV. They also said it was OK if I fitted it adjacent to a window and extract vent.
  4. justlead1

    justlead1 Trusted Plumber GSR

    Ventilation of drainage and soil systems has been part of there design for a century or more.
    Its purpose to provide a permanent circulation of air to disperse any build up of foul gas, reduce negative or positive air pressure that will blow trap seals, and provide self cleaning of pipes as the circulating air drys products that may be adhered to pipe wall. The crazed effect allow water on the next flush to self clean the pipe work to a degree.
    Fitting AAV was for me a great idea when it came to making money as they provide a big saving on both material and labour. However taking money out of the equation does make me think do they provide a better system for the client?
    • Like Like x 2
  5. Matchless.plumb

    Matchless.plumb Trusted Plumber GSR

    Totally agree , very informative.
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