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Discuss Venting of foul drain in the Plumbing Forum area at

  1. gatewaytothesouth

    gatewaytothesouth New Member

    I'd be grateful for some advice from any drainage gurus here!

    I'm about 5 years now into building a small bungalow in the woods which is now wind and weatherproof. At the rate I am going it will probably take another 5 years to complete it - I keep getting stuck on details and this is the latest.

    I've finished all the underground drainage which was signed off by building control a few years ago. The layout is shown in the attached schematic. You'll see that two 4" waste pipes have been brought into the building through the floor slab. The upstands have been cut back to finish floor level so they will be a pain to connect to but that's another story.

    The plan was to connect one WC to each of these wastes and connect the wastes from sinks and baths via stub stacks. I thought I could get away with direct connections to the drain but it seems I cannot - I understand an open vent is required since I am at the head of a long branch drain.

    I don't wish to fit an internal or external vent stack since both would be a real headache to install now and would really kill the overall look.

    Can anyone advise whether an open vent is strictly necessary in these circumstances? If it is, then I wonder if I could provide one that vents remotely from the building? Put another way, could I just vent the last inspection chamber via one of the unused 4" inlets? I could terminate this with a ground vent or short stub stack somewhere in the woods where it really wouldn't matter if the air got a bit squiffy.

    I'm sure my Building control officer would provide a definitive ruling on this but I'm afraid to ask - sometimes its easier to beg for forgiveness than it is to ask for permission!

    Your advice would be much appreciated.



    Drainage schematic.jpg
  2. Jim Goodenough

    Jim Goodenough Plumber

    Hi Jon, I don't see why your idea of venting from IC 1 in the woods wouldn't work as long as your fitting air admittance valves (let air in but not out) to the 2 stub stacks to the WC's
    • Creative Creative x 1
  3. Ric2013

    Ric2013 Plumber Top Contributor!!

    My recollection was that the head of the drain needs to be vented, but my gut feeling is that as long as there is an open vent reasonably close to the stub stacks, and that there is no likelihood of the drain between the IC that is vented and the stacks further upstream running full-bore, you'd be okay in some respects.
    Obviously the vent pipe would have to be a proper vent, not a low thing for rats to run in and out of, and you may need to consider how the horizontal drain to the vent pipe will avoid being an unused section which will tend to block and make a nice nesting place for rats. Perhaps you might need to find an actual use for this section of pipe, such as being the waste from an outbuilding?
    Just thinking out loud really, not a drainage 'expert' myself.
    Last edited: Feb 11, 2018
  4. SimonG

    SimonG Trusted Plumber Top Contributor!!

    Same here. Head to be vented and not durgo.
  5. gatewaytothesouth

    gatewaytothesouth New Member

    Thanks to all for taking the trouble to respond.

    I'm glad none of you think my proposal is a deal breaker - you've now given me the confidence to run it across Building control.

    I will come back with a separate issue shortly - once I have done a drawing.

    Kind regards,

  6. Jim Goodenough

    Jim Goodenough Plumber

    let us know Jon, we're waiting with bated breath!!;)
    • Like Like x 1
    • Agree Agree x 1
  7. johnduffell

    johnduffell Member

    Personally I'm with ric, the extended part would effectively be a redundant drain section which is prohibited under building regs due to the possibility of vermin. You'd have to be very careful.
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