Soil stack venting

[mawo]

Hi all,

Looking to move a soil stack about 550mm (then back 550mm in the void below the house) to allow for some wider windows to be put in downstairs. At the same time we're doing the bathroom upstairs, taking one dingy en-suite and merging it with the equally dingy bathroom next door into one respectable bathroom. This means ditching toilet 2 from the diagram.

Above where the soil from the toilet joins the stack is just venting. I'm wondering what the difference is between option 1 (swept tee, with the branch being connected to the vent, in a horizontal usage) and 2 (offset purely in the "vent" part, longer run of soil into upright tee branch) if there is any, and I've seen different advice on using 135s vs 92.5s to create the offset. I'd guess it doesn't matter so much in option 2 since above the connection to toilet 1 it's just vent and air isn't fussy as long as it can go up, but interested to hear your thoughts.

 

[muggles]

Can the ground connection not be moved to make the whole stack vertical? This work is notifiable to Building Control so it's worth asking your local inspector what they'd be happy with before you proceed

 

[mawo]

Unfortunately not, continuing it vertical from the new offset location would go right through the middle of a new window in the bathroom.

Had planned to asked BC when they're over next week, but wondered if there was any gotchas with either way. Have seen a few example where a tee has been used horizontally to continue the vent and the "horizontal" has continued into a WC, but wasn't sure if that was bad practice or not!

 

[Hugh Jaleak]

Bends in the 'Wet' part of a stack are frowned on, as Muggles has said, can the drain be moved across 550mm to allow the stack to drop vertically into it and avoid the offset in the underfloor void? Stacks should have a Long Radius bend at the bottom to allow smooth passage of the falling soil into the horizontal drain, shorter radius bends below a vertical section can create noise, as the falling waste hits the bend with force before carrying on along the pipe.

If you can achieve that at the bottom, either option 2 or 3 would be fine.

 

[mawo]

Thanks muggles and Hugh, I'll have another look under the floor to see if we can't shift the whole thing, might be sat in concrete however. Failing that, something long like this to bring the stack back to the main drain?

https://www.screwfix.com/p/87-5-double-socket-rest-bend/12719

 

[Hugh Jaleak]

That's the bend you need. (Or the equivalent clayware version, depending on which material you want to use. )

 

[mawo]

Cheers Hugh! I assume it can be a tighter bend back into the vertical stack? Went for another look under the floor, it stack is currently 100mm offset from the floor drain anyway - so actually it'd be a 450mm offset instead.

 

[mawo]

Taken before I pulled all those dead alarm cables out!!