Sydney has a significant under supply of housing both apartments and low density. 

The NSW   government is releasing new housing subdivisions in the west however these areas are a long drive from the city generally on a slow moving carpark known as a tollway.  The alternative is to live in an apartment high in the sky. 

There is a third alternative. 

A duplex, by dividing the typical Sydney residential lot into two houses a duplex or dual occupancy is created.  A second home is created for a little more than the cost of the building.