Bathroom waste pipes and when are air admittance valves needed

[Roz]

I’m doing my own plumbing and think I have overlooked the waste plan a bit. House is pretty simple with single upstairs bathroom including bath with shower over, basin and toilet. 
 

below this is the kitchen with the kitchen sink. 
 

I have some waste pipes in place but I am now confused about whether and where I need to add air admittance valves. I had thought I just put one on the top of the soil stack, to which all the bathroom wastes will run, but now I am not sure? Do I need individual ones on e.g. the basin? I’ve attached a quick diagram of what my thinking was until now. Thanks so much for any advice!

[Conor]

One AAV on the main stack is enough. Of you can, run the 110 pipe as close to the bath as possible, right to it preferably.

[Roz]

4 hours ago, Conor said:

One AAV on the main stack is enough. Of you can, run the 110 pipe as close to the bath as possible, right to it preferably.

Oh this is good news! The pipe is downstream of the bath, and it’s about a metre or 1.5 metres away? 

[Temp]

If your stack goes above the roofline you don't need an AAV at all to meet the regulations.

 

There is a small chance you will need one on the pipe run to the bath. Fast flowing water from the WC or bath might suck water from the bath or basin traps. Ideally run these smaller  pipes separately to the stack or make provision for an AAV on the left past the bath. @Conor's suggestion of running 110mm pipe to the bath would also work.

 

Any AAV should be higher than the other things like basin waste. I think the idea is two fold..  if a pipe becomes blocked water levels become visible in the basin before the water pours out of a hidden AAV and it also stops the AAV becoming contaminated/blocked.