Can I fit an AAV externally to replace the S&V pipe?

[RrogerD]

I'm aware that external AAVs are available, my query is: can I use one to replace the current (rotted) S&V and if so, can I get away without it needing to exit above the highest window?
As per the pics, I'm dealing with a high, 3-storey building. Access to replace the cast-iron pipe will need scaffolding at £1k a pop.
The flat roof btw is being replaced as I type, with EPDM rubber sheet and the rainwater pipe re-jigged to drain directly on to the roof rather than my heath-robinson affair seen here.
Edit:
I've just seen this thread on here as it happens. 6 pages!
I think that the gist of it is that it is ok and, does not need to be 900mm from a window. Feel free to correct me if I am wrong.
https://www.diynot.com/diy/threads/external-air-admittance-valve.612572/

 

[denso13]

Better with an open vent, but yes, you could fit one lower down.

 

[Hugh Jaleak]

Drains need to breathe out as well as in! I would be very wary of changing an open vent for an AAV, as you're essentially then sealing the system, and could well find you start experiencing issues you didn't have before....

Assuming you'll have a scaffold of sufficient height to safely remove the top section of cast, I would be replacing like for like whilst access is available. Getting back up there at a later date to swap an AAV for an open vented section isn't going to be straightforward at that sort of height.

Advice is given based on over 30 years of experience in Plumbing and Drainage, having re read through the thread you have linked to in your initial post, I am reminded why I stopped commenting....