how small can I make a soil stack vent??

[JingleyJen]

It's JingleyJen's husband here....

I've currently got a soil stack that serves a WC & sink in the downstairs cloakroom and a WC, sink, bath and shower upstairs. The soil stack currently vents to atmosphere through the roof.

Above the level of the WC I'd really like to reduce the diameter of the vent to as small as possible so that I can go round some tight corners before re-joining with the existing roof vent. I do not want to use a dergo AAV.

What is the minimum diameter of vent pipe that I need/must have? I believe that I can go down to 3" pipe, can I go smaller to say 2"?

TIA for any advice.

Have you tried the screwfix messageboards? They have been great for me.

DP thinks (but isn't 100%) that you can go to 2" but suggested that you phone building control at your local council -they'll happily answer queries like this . DP uses them all the time as, although hes a builder, regulations are changing all the time.