Between 2001 and 2006, the rate of growth in the number of households in Sydney, Melbourne, Brisbane, Perth and Adelaide was greater than the rate of population growth. This indicates that although the population was increasing the new households kept forming at a faster rate, meaning that there were dwellings available and affordable for them to move in to and ‘form’ households in.
Between 2006 and 2011, however, this trend reverses. Rates of population growth quickened but rates of new household formation did not keep pace. This indicates that a significant number of people were not forming new households.
The reasons for households not forming include either a lack of dwellings (i.e. insufficient supply) or a lack of affordable dwellings.

Source: ABS 2011 Census of Population and Housing. Time Series Profile.
Rates of population growth quickened but rates of new household formation did not keep pace.