You mentioned Secondary Dwelling? What is it?
Secondary dwellings are part of the State Environmental Planning Policy known as (SEPP), and are classed under the Affordable Rental Housing component of this legislation. This is intended to make the process a lot easier for homeowners to meet building regulations. As such Granny Flats have the status of a complying development, which have an expedited approval process, with authorisation normally processed in as little as ten days. Complying developments are generally smaller structures such as alterations, awnings, carports, garages, decks, patios and swimming pools. A Complying Development Certificate can be issued by your local council or an Accredited Certifier.
There are a few places on the Internet to learn and discover regulations, legislation and laws concerning Granny Flats in Sydney and New South Wales, I have however found one site that seems to be filling this void of knowledge for mums & dads and investors. I highly recommend reading some of the articles which can be found here, basically what they have done is made sense of complicated laws and regulations around secondary dwellings.