Does an AAV have to be 100mm?

[Sadruddin]

Hi. I have the following:

Toilet, sink and shower on ground floor to below floor waste

110mm from the toilet running up a corner in the ground floor to:

toilet, sink and shower on the first floor.

There is no roof vent, so I want to use an AAV on the first floor.

Do I have to use one as big as 110mm, or can I fit an off centre reducer, (sorry, not sure what this would be called, to, say, a 40mm pipe up the corner of the room, ending in a smaller AAV above the height of the sink waste.

Sorry of this is unclear, if it is, happy to explain further.

 

[denso13]

ending in a smaller AAV above the height of the sink waste.

It doesn't necessarily have to be above the height of the sink waste depending which AAV you use.

or can I fit an off centre reducer

A type A1 valve can go below the spill level and could possibly go here, but not quite enough info.

 

[Madrab]

40mm may be too small to vent a toilet, you may get away with a 50mm but even then you don't really want to vent smaller than the largest pipe that the vent has to protect.

Added to that, you need to make sure that your waste/drain/sewer is positive vented, many problems can occur when everyone gets rid of their open vent without consideration.