I'm moving my bathroom to the adjacent corner in my house, and would like to know if I need to vent my soil pipe with my planed system before it reaches the existing external soil stack. Going directly through the floor is not possible as drilling holes through the joist will weaken them. Also, I can not exit out the rear of the property.

So my plan was to allow my toilet to connect directly down into a manifold so sink and shower can connect too. From there the pipe will travel vertically for approx 2.4 meters, then to a couple of 45 elbows to bring the pipe work to horizontal and to offset no more than 200mm, then it would run for approximately 4.5 meter before connecting into the external stack.

Does this branch require venting from the bathroom end?

If so can it be done internally with some kind clever vent?


3 Answers 3


The plumbing code and good common sense requires that you vent every fixture somehow.

I am not a plumber but in my reading of their code this branch would require a minimum of a 2" vent for the bathroom group run up to the attic and through the roof or terminate in an air admittance valve a minimum of 6" above the flood rim of the highest fixture (sink). (Some people hate AAVs, some say they are fine.) The waste line would have to be a minimum of 3" to the toilet and the shower and sink should have their own vents joining the main vent. These need to go vertical until they are at least 6" above the flood rim of the sink.

I am sure there are some finer points a real plumber could show you but the gist of it is: every fixture needs to be vented or you will siphon the trap and have sewer gas backing up into the house and boy will you be sorry then. A little plastic pipe now will save you from being very unpopular later.

Good luck!

  • The key part, as you mention, is that every fixture needs to be vented. One clarification to your comment is that you do not need to individually vent each fixture (this would be called individual dry venting). You can vent the toilet and the shower through the sink’s vent via a method called wet venting. This method requires certain requirements to be met, mostly that the last fixture connected is the toilet and that the wet portion between the toilet and the sink’s vent is sized as a wet vent. Local codes should be check for their requirements.
    – pdd
    Jun 5, 2016 at 20:11

I dont know how different codes are were you live but in the United States you would need a vent. Maybe you can reuse your old vent. I know you said its on the opposite corner but if your running the pipes in the basement/crawlspace it wont be that bad. You may be able to vent out of side of house too. We have special automatic vents but it is only for sinks.


It CAN be done internally. Genova makes a very clever little diaphragm vent that glues right into PVC drain/soil pipe. It should not be installed in an inaccessible location, since it may possibly need periodic maintenance and if it fails, you wouldn't want a methane buildup inside your walls or anywhere else in the house... so it must be exposed.

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