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!