Can I use 90 degree bends in dry soil vent?

[dave100]

TL/DR: Can I have a bend of 90 degrees in the dry section of a 4-inch soil vent?

Hi. I am renovating a small bathroom. There is an awkward part of the wall where the builders boxed off a large section just to conceal the 4-inch soil vent. I realise, of course, that the soil vent is essential to the plumbing system in my apartment and the 5 below it (I am on the top floor of a 6-storey building) but if I could conceal the 4-inch pipe in the ceiling cavity and the wall cavity that would allow me to remove the ugly boxed section of the wall and have a nice tiled straight wall.

This soil vent serves my apartment and the 5 below me. I understand that the 'wet' part of the pipe, where waste flows, should not have 90 degree bends but I am wondering of this applies also in the 'dry' part used to allow sewer gasses to escape to the outside which is the flat concrete roof above my bathroom.

The image above illustrates the situation.

The area in the ceiling cavity is only about 15 or 16 inches tall, its just the area where the timber joists run, but there would be enough room there to use a couple of 90 degree bends to run the pipe over a bit and down to connect with the existing pipe, connecting above the 'wet' section where my toilet connects to the pipe.

I appreciate your advice!

 

[ShaunCorbs]

Best to use 45s but aslong as it has a fall back to the drain eg always flowing your fine

 

[dave100]

Thank you @ShaunCorbs

I don't have room for 45s but I probably wouldn't need 90s either, I would use adjustable bends and would be able to get the angle down to between 80 degrees and 70 degrees.

When you say 'always flowing' are you taking into account that this would be the dry part of the pipe and there would only be air from outside the building being syphoned in to that section when a toilet is flushed etc?

I appreciate your input, thanks again!

 

[king of pipes]

As Shaun is stating it shouldn't be a issue but always allow a fall back to drain there will be a build up of condensation in the pipe and a ingress of water from rain and snow . Regards kop

 

[dave100]

Ah, yes, that makes sense. Thank you KOP, thank you Shaun. I will have a downward slope of around 10 degrees, perhaps 20 degrees using adjustable bends (rather than the current 45) so I will be able to maintain that fall back to the drain.