When is stub stack not a stub stack?

[Jezwald]

I'm confused.
I have a ground floor toilet that discharges to a stack outside which in turn runs to the main drain.
The stack outside is about 1m higher than the soil pipe from the toilet, and terminates in an AAV.
I've seen a post somewhere that suggest that if the stack is ventilated, it isn't a stub stack, but I'd be grateful for opinions and/or definitions!

Many thanks

 

[Hugh Jaleak]

Stub stack can be ventilated or unventilated, depends on the setup of the drainage system. Part H of the Building Regs explains it in more detail.

 

[^woody^]

TBH, I think a "stack" be it stub or main, must be ventilated (open or AAV) else it's not a stack, just a bit of vertical pipe.

Generally a stub stack is a term for a secondary or minor stack connected to the system, with specific location and height above invert criteria, and tends to terminate just above the highest connection to it.

 

[Jezwald]

Thanks for the replies.
It's looking like I have a problem with a proposed project.
I had hoped to install an ensuite with just toilet and basin in a bedroom on what is, from a drainage point of view, the first floor.
The existing soil and vent pipe is on the back of the house, and it drains away to a septic tank.
The stub stack for the downstairs toilet runs to a chamber where it meets the main soil waste and 2 gullies, from the kitchen and the washhand basin in the downstairs WC
Is there a way to get the drainage that I need from the ensuite, marked with an X on the attached drawing?

 

[23vc]

Can’t you just extend the existing stub stack upwards and branch into it then vent the top?

 

[Hugh Jaleak]

Are you able to extend the existing stub stack upwards and across to your proposed En Suite position? Then bring the 110mm pipework up in a corner of the room, and fit an AAV there, (needs to be above the spillover height of the basin.)

 

[Jezwald]

Can’t you just extend the existing stub stack upwards and branch into it then vent the top?

That’s what I was hoping to do, but I was concerned about the branch being > 2m rule.
Would it need venting, or could I keep the AAV? There’s a window just round the corner

 

[23vc]

Can’t picture the 2m rule but yeah you can use an external grade aav

 

[Jezwald]

Branch 2 m above invert of drain?

 

[Hugh Jaleak]

Branch 2 m above invert of drain?

Not really any different to a conventional soil stack, just check depth of drain first, make sure the invert of the drain is a minimum of 450mm below the lowest connection onto the stack. Ideally should have a rest bend at the bottom, but too late for that now. How far is it from the bend to the next manhole, (if too close there is a danger of waste flying into the chamber at speed, and fouling the opposite benching.)

 

[Jezwald]

The chamber is around 4m away, and the drain runs round ~45degrees before it gets there. Flushing the downstairs WC doesn’t cause a rush, and hopefully the bends will slow down traffic from the en-suite. I don’t think there will be much use - it’s primarily night time use and morning wash.
Really appreciate all the help and advice.