Air admittance valve - vs- open vent pipe

8 Feb 2010
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United Kingdom
Are there any appreciable drawbacks to fitting an AAV rather than having an open vent pipe on a soil stack? Reason being.... the architect 'missed' the provision of a soil stack in our extension. I have worked out a way of including one, but it means a tortuous run of soil pipe through the roof void with a handful of elbows and a good 9m of pipe! Then I need to go through the roof with the vent... so it won't look great. This seems to be necessary as the roof has skylights fitted and trying to comply with building regs so the soil vent is at least 3m away from any opening within 900mm vertically means there are only a couple of places the vent can go.... all miles away from the stack!
Looking at it logically, the simplest solution is an AAV pretty much right on top of the soil stack in the en-suite... boxed into a cupboard and above the spill over level. The stack is taking 2xWC, 2Xshower, 2Xhand basin, 1Xbath for normal family use and feeds into the ground floor soil pipe taking 1xWC, washing machine, 2Xhand basins.... which then all run on to the manhole and main sewer. The vent pipe or AAV would be the only open vent to atmosphere for the whole lot.
Am I asking a lot of an AAV to serve this? and do they have any particular problems? or do you reckon it would be alright? It would sure save me a heck of a lot of work (and cost!).....
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simply put, the "best" option is an open vent, as it is open to the atmposphere nothing can happen to it, however there are thousands of AAV's fitted and they work perfectly well, in theory it could jam at some time in the future, if it jams closed the appliances will not run away properly, if it jams open there will be a smell, if it happens change the AAV, given the description of where you need to run the pipe to and the cost, to take it outside it would seem a no brainer, just remember it needs to draw air in so dont box it in completely
May be a question mark over whether BCO will pass the works though, you need at least one open vent on the system to comply, otherwise there is no facility for releasing positive pressure within the system.

I'm unsure if you've got the measurements mixed up, but any vent must terminate 900mm above any opening within 3 metres. Regs, page 16.
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Thanks for that, yeah - I need to double check with BCO... am hoping it will be ok as there is another stack at the other end of the house which does vent to open pipe, so hopefully any 'burps' will blow through that one although it is a pretty long run of pipe to get there.
I don't think I explained myself very well with regards the regs.... I know its 900mm above any opening within 3m - my problem is that I have opening skylights just under the ridge, (so I can't get a pipe to terminate 900mm above them unless I have a 1m length of pipe sticking up from the roof!). Consequently I need to try and get 3m away from them and still be 900mm above the other windows in the walls... leaving only a couple of places to terminate and all at the end of monster/tortuous pipe runs.
I am guessing there is no limit to the number of appliances you can have served by a single AAV?

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