If the 8M leads directly to the soil stack, I still cant see the nead
for the stub stack & AAV. However, if you feel this is a must have,
then i'd recommend taking a smaller dia pipe up to loft level
(Assuming you own all the floors above you:=)) and then fitting the
AAV there. However, as long as the stack is vented, I don't see it
being needed.

It was building regs who suggested the AAV on a 1m stub stack so I took it
as read really (don't know if it makes a difference, but the 8m is via 3 90
degree bends!). Hadn't thought of running it all the way up to the loft -
good idea! How would that work then? Could I just put a strap boss on the
soil pipe to the left of the toilet and run 40mm to the loft? If so, can
you get AAVs that fit to 40mm pipe? That would certainly be much more
practical.

Cheers!

Andy