Air Admittance Valve

[ln1234]

I've been reading through recent posts on this, but am a bit unclear exactly where to put the AAV, or if in fact I need one. I will have 2 new toilets connected on the first floor like the digram below.

There is already another toilet on the 2nd floor (soil stacks run horizontally through the house with a drop). As the 2 toilets connectbefore the Basins to the soil pipe, do I need an AAV at the end of the pipe (before the toilets)? If so, where should it be positioned and how high does it need to terminate?

 

[chrishutt]

No need for AAVs, unless perhaps the WC branches are extremely long. I think you're OK up to 6 metres anyway, but you can check the regs (building Regulations H1) at the Office of Deputy Prime Minister site.

 

[ChrisR]

I'd put anti-syphon traps on both the basins in case a piston of waste from the wc's pulls the trap in the basin. COuld also be an issue with a bath, though any waste shared by a basin and bath before the horizontal wc soil bit, would be protected by the one anti-siphon valve (which is an air admittance valve). "Stack" by the way I think always means a vertical pipe like the one outside.
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