Relocating toilet soil pipe under upstairs bathroom floor

[Carlosfandango1971]

Hi All,

I'm currently in the middle of an upstairs bathroom remodel and am considering whether I can move the existing soil waste pipe to the toilet to under the floor boards.

The current situation is this:

- Vertical stack that pops up, just under the floor
- Bathroom shower 40mm feeds into soil stack
- Toilet, feeds into stack but 110m waste pipe routed above the floor, into an elbow which then goes down into the stack

See attached over head diagram.

What I would like to do (if possible), is to sink the 110mm pipe to the toilet under the floor. The joists are not solid ones, so there is a gap of approx. 130mm between top and bottom of them.

My issue is I feel I would need a something like this to feed the shower waste as well as toilet (capping off the top) but it will likely be too big to go under the floor: https://www.screwfix.com/p/floplast...ocket-soil-branch-anthracite-grey-110mm/637kj

I have however seen these on e-bay (see other attachment) and was wondering if this would be a possible option? This would simply slot into the top of the stack under the floor, allowing me to feed the 110m under the floor to the toilet and have my shower go into the boss on the side.

Thoughts / advice would be much appreciated.

 

[i_am_fubar]

I'm a little alarmed that you say the stack just ends. Do you have any ventilation to prevent syphoning when you flush the loo?

 

[Carlosfandango1971]

You are correct, it simple ends and has no ventilation, which is probably why when we flush the loo we can sometimes hear it gurgling a little in the shower/sink wastes. Not sure what I can do to prevent it now??

Note: The other two stacks we have in the house are vented up through the roof.

 

[i_am_fubar]

Stick an Air Admittance Valve (AAV) at the top. it's basically a check valve that allows air in when there is negative pressure in the pipe.

Be careful with waste pipe flow directions. Having a Cross with two horizontal (ish) intakes can lead to poop coming back up the pipe. Always stagger them, have a lead in angle or at minimum have them 90 degrees to each other.