Old style vent pipe reduction in size?

Discussion in 'Plumbers' Talk' started by stu worth, Sep 19, 2014.

  1. stu worth

    stu worth New Member

    Hi gang , newbie here.
    I have an old style stink pipe outlet that is 110mm ?? ,my question is can i reduce the size half way up to say..something like guttering pipe as there is no clearance from the outlet pipe and it will not physically fit up the wall. A smaller pipe would just about do it with a home made connection)
    (i am not going into the guttering i just want to know whether i can use the pipe as soil pipe venting only)
    Oh ,i need to get this signed off by the building inspector so need an answer thats legal and not just something i could get away with.
    Cheers everybody.
     
  2. stu worth

    stu worth New Member

    Oh.. and does anybody know how high the vent has to be above the highest window it is next to?
     
  3. Phil the Paver

    Phil the Paver Screwfix Select

    the smallest size you can use on a main vent pipe is 75mm, I'm not sure you can use rainwater pipe for this purpose, I've never altered the size from 110mm, if i remember rightly the pipe has to be at least 300mm above the gutter line.
     
  4. stu worth

    stu worth New Member

    Fabulous ,that really helps, thanks very much :)
     
  5. tom.plum

    tom.plum Screwfix Select

    On a new build I was on once we reduced the size of the vent to 50mm to get it into the attic an vented throu tile vents, it was ok'd by the BCO, :)
     
  6. Jitender

    Jitender Screwfix Select

    Could they install a Air admittance valve? The stack needs to vent 900mm above a wi dow opening within 3 meters. But i have seen many which are not.
     
  7. stu worth

    stu worth New Member

    Thanks Tom and I'm afraid I am doing the work myself as the builders are not interested in correcting their mistake so I do not know what an air admittance valve is. Cheers.
     
  8. Jitender

    Jitender Screwfix Select

    An AAV prevents foul smell emanating, but admits air into the stack. They are limited in use to dwellings of no more then 3 storeys, in upto 4 adjacent buildings so long as the fifth stack terminates conventionally. They are terminated inside a building.

    Or as Phil has mentioned the stack can reduce to 75mm min. if its serving a WC or;

    'the internal dia. of the stack should not be less than that of the largest trap or branch discharge pipe'.

    Screwfix sell 'internal' and 'external' AAVs


    http://www.floplast.co.uk/products/soil-and-waste-systems/air-admittance-valves
     
  9. Jitender

    Jitender Screwfix Select

  10. itchyspanner

    itchyspanner Member

    82mm (3"/75mmID) is the smallest you can fit to meet the building regs. As for height its 900mm normally above a window.
     

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