regulations around soil vent pipe

[CharlieB1981]

looking to reinstate an old downstairs toilet and not sure if this needs a vent pipe as the old one's previously been removed, old waste pipe still intact to connect to.

current set up.
soil pipe heads from the toilet, under the porch to an outside manhole cover (2.5 meter run) then turns 90 degrees, runs a further 5 meters to another manhole cover where the main bathroom connects from the first floor and has a vent pipe extending to the roof.

plumber tells me this wont need a further vent pipe and reading part H i'm confused but thought all sewage needed a vent pipe for waste smells

 

[noseall]

Only the head of the drain (highest point usually) requires venting, i.e. one stack only required.

 

[seasickstevie]

So this is a 7.5m branch, and doesn't need a vent?
I would've thought maybe an AAV might have been a good idea to help the movement.

We've got a similar length run in our downstairs loo with no AAV, and it's always more likely to not flush adequately than the upstairs loo.

I have considered putting in an AAV to eliminate this problem.

Alternatively I had considered the option of extending with a 2" SVP vent into the loft and through the roof - would that make sense I wonder?

 

[noseall]

So this is a 7.5m branch, and doesn't need a vent?
I would've thought maybe an AAV might have been a good idea to help the movement.

I did not say that it did not need an AAV rather that the drain system does not require another SVP.

 

[Blagard]

Charlie, did you understand the terminology?

An AAV is an Air Admittance Valve - and this allows air into the sewer only (not out) so traps don't get pulled (sucked out) by a negative air pressure in the drains

The soil and vent pipe also does that, but it also allows a release of positive pressure in the drains. So long as the drain does have a vent pipe at the head of the drain then another is not required.

Your second manhole does have a vent and that is important because that has become the head of the drain.

Reading your post it seems that there was an old soil and vent pipe at what was the head of the drain. If the manhole outside the porch is just to change direction of the pipe, i.e. not including another branch then the whole 7.5m run could be considered a branch. As this branch is less than 10m no other vent stack is required.

However, if your drains are subject to flooding then you actually need a full vented stack (not even an AAV).

On checking the 10m for a branch I struggle to find where I got that from! - So if anyone can correct or confirm it would be appreciated!

There is a maximum invert depth that a direct WC "branch" can go to relative to the floor level i.e. 1.3m. Above that presumably an AAV is required?

 

[CharlieB1981]

Cheers for the replies, everyone.

Blagard -understand the terminology, thanks for checking,
the manhole outside the porch is just a change of direction for sewage but there is a rainwater outlet that sticks out a foot above for the water to drop in to the sewage pipes.

I'd planned to fit an AAV anyway just to assist with any flow.

Thanks for the help all