@Austman said:
Also, it’s likely such a major renovation (moving walls or creating new rooms) needs council approval … You generally do need council approval for “reconfiguration of internal space by moving or removing walls, new window and door openings”.
My neighbour removed a wall, extending his lounge room into the space occupied by a third bedroom, meaning it now adjoins the bedroom of the next door flat. City of Sydney council said they had a certificate from the builder saying it was “exempt” and didn’t need a DA. The EC said they had a letter from the council saying it had been approved. The council said they had no right to check and if there was a problem we should take it up with the builder who issued the certificate. So maybe the need for approval isn’t as “likely” as you think.