I'm having a conservatory built. All my plumbing is being moved except for the vent stack. I won't need it to vent pipes, but it's venting a drain also used by nearby properties. The builders have cut the vent stack to approximately 2 feet above ground level. My question is: Should they have relocated it, as it'll now be in the conservatory? I understood vent stacks were for releasing gasses but the builders informed me it's a fresh air vent.

  • 1
    "A fresh air vent". That's a good one...I've got to remember that one. So, they cut it off 2' above ground level so it can't get fresh air now...c'mon... I agree with Trevor, move it.
    – Lee Sam
    Commented Mar 19, 2017 at 18:19

2 Answers 2


Say what now..... connected to other drains ... opens in your conservatory....

What are they thinking...

You will be subject to all kinds of gasses, and SMELLS, and possible the odd rodent returning up the pipe.

Even if there is some kind of trap down there that prevents backflow, the pipe will suck air from your conservatory and make noise.

Tell them to move it.

  • Thanks for agreeing with my thoughts, they think I'm stupid. Glad I'm not alone in thinking it's wrong and it's for gasses to escape, not air to go down.
    – Kim
    Commented Mar 19, 2017 at 21:09

To clarify, the purpose of a plumbing vent (sanitary vent) is to protect the trap by preventing siphoning of the water out of the trap when fixtures are used. So the intent is to allow air into the system. However, due to the fact that the vent is connected downstream of the trap, it is open to all the sewer gases with in the drainage system and as a side effect will allow sewer gas to escape. This is why there are rules limiting the location that a plumbing vent can terminate. Codes very by jurisdiction, but they will often provide limits such as the following:

  • be located on the roof
  • not less than 1 m above or not less than 3.5 m in any other direction from every air inlet, openable window or door
  • not less than 2 m above or not less than 3.5 m in any other direction from a roof that supports an occupancy
  • not less than 2 m above ground
  • not less than 1.8 m from every property line

There is also another type of plumbing vent called a fresh air inlet. This is a vent pipe that is installed in conjunction with a building trap and terminates outdoors. The termination of a fresh air inlet is not restricted as the above sanitary vent is.

  • Can you elaborate on what fresh air inlets are and why they are used?
    – Grant
    Commented Mar 27, 2017 at 22:43
  • In all my years, I've never seen a fresh air inlet (that I'm aware of). They are used in conjunction with a building trap. I have never seen a building trap be installed and I believe this is an older way of doing things that is no longer required but is still part of the code and does exist in older homes.
    – pdd
    Commented Mar 27, 2017 at 23:10

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