Adding downstairs toilet onto same stack

[Jayne89]

Hi guys,
Just after some advice on adding a secondary toilet to the underneath of our highest house.
I'm sure our regs are probably a bit different being that I'm in Australia but just want to see if im on the right track with my thinking.
Looking to add a P trap toilet to the lower level of our downstairs house. The toilet upstairs sits directly above where we would like to put the new one.
Is it possible to use a Y type join and connect the new loo to the existing vertical stack pipe? I have attached a picture to show the location of the pipes and proposed placement of toilet. Please don't mind the mess, downstairs is currently harboring junk.
Any advice is appreciated.

 

[Terry]

All of the plumbing downstairs will need venting.
Without the venting, it pulls the water seal out of the bowl.

 

[Sponsor]

 

[Jayne89]

Thanks for that. So just to clarify I am understanding right... As long as the downstairs toilet has its own vent pipe I should be right to connect it onto the stack pipe?
Nothing else in that powder room will be connected onto it as there is other draining for basins so it will purely be the toilet.
This is the vent pipe for the upstairs toilet.

 

[HollyB]

I would

Thanks for that. So just to clarify I am understanding right... As long as the downstairs toilet has its own vent pipe I should be right to connect it onto the stack pipe?
Nothing else in that powder room will be connected onto it as there is other draining for basins so it will purely be the toilet.
This is the vent pipe for the upstairs toilet.

I would like to know the answer to this as well.

 

[HollyB]

Also in your diagram it shows basement pipes under/in the concrete flooring. Would it also work if I built a subfloor to install my plumbing under instead of breaking concrete, then go through the existing stack as long as there was separate ventilation? Or can the ventilation from the new toilet go to the existing vent pipe?

 

[Reach4]

I don't know Australian codes. I am not a plumber. However it is unusual for a toilet to need its own vent for performance reasons. In the US, toilet venting is a lot more permissive with the IPC (International plumbing code) than it is with UPC, which Terry works with. International does not mean that Australia uses it. IPC is more permissive IMO because it is more attentive to what works rather than what is convention.

You want the other things to have good venting. A toilet does not need a vent to avoid siphoning. You want siphoning in a toilet, and the trap refill water fills up the siphoned trap.