New South Wales Consolidated Regulations(cf clause 41 of EP&A Regulation 1994)
(1) Development consent is required for any alteration or extension of a building or work used for an existing use.
(2) The alteration or extension:(a) must be for the existing use of the building or work and for no other use, and(b) must be erected or carried out only on the land on which the building or work was erected or carried out immediately before the relevant date.