There are many competing definitions of affordable housing. The National Affordable Housing Consortium uses the definition developed by the National Affordable Housing Summit Group*.
“Affordable Housing is housing which is reasonably adequate in standard and location for lower or middle income households and does not cost so much that a household is unlikely to be able to meet other basic needs on a sustainable basis”
* The Summit Group consists of the: Housing Industry Association, Australian Council of Trades Unions, Australian Council of Social Services, The Community Housing Federation of Australia and National Shelter.
Other definitions use a benchmarking approach. For example, that housing costs should be less then 30 per cent of gross household income. This is a generally useful guide for households in the lowest 40 per cent of incomes.
However affordability is not simply a matter of housing costs. A well located dwelling might save significant household travel costs and therefore improve overall family economics, even if the rent is higher than a dwelling in a poorer location.