Allowing Air Flow into Soil Stack System?

I'm installing 4 soil stacks into my new build. With each of these can I simply put a 4" AAV near the top of the pipework to allow air to enter the system, rather than run the pipework up and out of the roof with a normal vent?

Thanks, Adam


Hello Adam

The design of sanitary pipework installations is not something for the inexperienced. I assume as you are carrying out a new build, you have a pre-approved design and layout for your pipes.

A good rule of thumb was always that the head of the drain run must be ventilated 'naturally' i.e. not an AAV in sight. The remainder may be fitted with AAVs, but it will be dependent upon their proximity to the ventilated drain. e.g. if they are venting an isolated sub-route of the below ground system, it may be wise to 'keep it natural'. - Naturally ventilated pipes will always be the best solution - anything with a moving part(s) always has the potential to go wrong.

You do not always need to go to the bother of taking a vent pipe through a roof; as it can always vent via a connection to a roof tile terminal. They key thing is to locate the vent point such that it does not discharge toilet odours near to an openable window - again this is covered under the building regulations. Vent tiles take away the problem of more costly vents that penetrate the roof covering and require sealing.

You are probably aware that AAVs must not be fitted in an external space, and they must enjoy a free-flow of air and be accessible for maintenance - these are part of 'Building Regulations'.

Once you have considered the above, the easiest resolution may well be a discussion on site with your friendly building control officer who is inspecting the build. They are usually fairly clued up on these things and will need to agree the resolution with you any way, so why not involve him/ her in your design from the start?

Some building regulations are more complicated than others, but the Approved Document that covers this work is that of Part H which can be downloaded from my web site here - and is unusually quite straightforward.

Hope that helps, Mark
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