One other question, does this type of renovation ever fall under exempt developments legislation in NSW i.e. no DA required? Or does this legislation only apply if attaching to a ground floor or to a house?
Have a look at Subsections 5 and 6 of the relevant SEPP (Exempt and Complying Developments). I suspect you may have to get this past your strata committee rather than the council, provided you comply with the standards laid out in the Act.
I don’t think it only applies to houses, as far as planning is concerned.