I'm building an extension and renovating my house at the same time. The house has an external soil stack that is open and terminates above the roofline. It goes down to just under ground and then under the extension and away to the main drain. The bathroom is on the first floor and comprises of toilet, basin, shower and separate bath. There is a toilet and sink going in under the stairs. The old kitchen is being turned into a utility room with a sink. The new kitchen has a sink in the island. Question is, can all that run off the main stack, or do I need AAVs and if so where! I've tried to draw the pipework on the plans so hopefully it makes a little sense. Any help is much appreciated!
You need one 110mm AAV where the old stack vent used to go through the roof. That's all you should need.
If I’m understanding it correctly, I would say no you don’t need one and it will all be fine off it’s open vent at the top of the stack.
I thought the question about where to put the AAV was because the OP was wanting to ret rid of the vent through the roof. If the vent through the roof is staying, then there is no need whatsoever for an AAV.
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