Soil Pipe Vent

I am planning a new Ensuite to a bungalow bedroom. The horizontal run of the WC soil pipe will be more than 4m (approx 5.5m) so I believe BR require a vent to be fitted. The drop over that distance is no issue as the ground slopes so I can easily exceed 1:40. For the vent I was thinking of running vertically off the soil pipe into the bungalow loft space and capping with an air admittance valve. Would a 32mm diameter pipe comply with regs or can I go even smaller? The reason for asking is because I could route through a new stud wall if the pipe diameter can be kept small enough.

 

Ok - thanks for info

 

Rehashing an old thread I started on reviewing my soil pipe options!

I have now read that the horizontal distance of a 5" soil pipe can be 6m and longer if AAAV fitted so am I correct in thinking an AAAV is not required if the run is under that distance? Soil pipe will have a shower and basin draining into it in 40mm pipe approx 1m downstream of the loo - am I likely to have the trap water sucked out of these with no AAAV? Would a HepVo or similar be an alternative to a AAAV?

The reason I am looking at alternatives is because the soil pipe run is under the suspended floor (bungalow) where there is plenty of room to instal valves etc but running a AAAV up into the loft space would mean boxing in etc. There is no issue with drop on any of the drainage pipes and underfloor height is approx 70cm so plenty of room there.

 

Thanks for the reply. So IF THE AAV was positioned between the loo and sink /shower drain outlet into the soil pipe it would stop any vacuum effect from flushing the loo sucking water out of the traps?

Any preferences on make/model of AAV?

 

Ahh - ok - makes sense that it must be higher than basin but scuppers my idea to have it in floor space!

Am I correct in my earlier post that an AAV is not required for less than 6m horizontal soil pipe runs? I can always have the basin/shower drain enter the soil pipe further downstream from the loo if that lessens any vacuum effect.