Vertical Offset in Branch (Plumbing 101)

[MortarThePoint]

Trying to understand various options for waste pipe layout. As I understand it, a  bath or shower waste has to be at least 40mm (max. 3m length) or 50mm (max. 4m length) diameter to the stack. It needs to fall at a rate between 18mm and 90mm per metre. However, can I have a short vertical section in it for passing through a floor (hollowcore concrete)? The layout below has a section of pipe above the floor for ~600mm, a vertical drop with two swept bends dropping a height of 200-300mm and then a section of pipe below the floor for about 2m. All in 40mm pipe. The 2m section below the floor joins onto the 110mm stack.

 

Is this only allowed if the is an AAV at the top of the vertical section?

 

 

[TonyT]

Doesn’t look like it would cause any problems, do use 50mm pipe, much better to have an air break in the pipe.

 

[Conor]

I did this, but the run suffers from gurgling as the two 90⁰ bends cause a bit of surcharging. I'd reccomend using 45⁰s instead, with about 200mm between them to keep the water flowing smoothly.

[MortarThePoint]

On 26/08/2023 at 16:07, Conor said:

I did this, but the run suffers from gurgling as the two 90⁰ bends cause a bit of surcharging. I'd reccomend using 45⁰s instead, with about 200mm between them to keep the water flowing smoothly.

Was that in 40mm pipe of 50mm?