Tina Holden, 48, with her son Maddison, 12. Credit:Edwina Pickles The research is based on 2014 data and measures "low income" as household income of just under $57,000. In this bracket, the household would have to be spending $328 a week on rent or less for it to be considered "affordable" - or about one-third of the income. The figure was similar for servicing a mortgage. Household middle income was calculated at about $142,000. One of the implications of the growing crisis is an increasing geographical gap between the ageing population in inner-Sydney areas and the people who provide services to them. Essential workers, or so-called "city makers" including aged care workers, nurses, paramedics and police officers, can now rarely afford to live near their jobs. If they do, they are having to go without necessities to afford a roof over their heads. Some, like single mother Tina Holden, are just one or two steps away from homelessness.

A hospitality manager, the 48-year-old was made redundant from her job at a Bondi nursing home in early July. The mother of a 12-year-old boy with mild autism, Maddison, was diagnosed with breast cancer three weeks later. In just a few months, her financial situation has gone from manageable to desperate. Her small redundancy payout is now gone, she is in debt to friends to the tune of $5500, but still needs to make the $560 weekly rental payments - 111 per cent of her income - on her eastern suburbs apartment. "I didn't foresee this. I haven't chosen this," she said. Ms Holden said she contacted the housing department – which has 60,000 individuals and families on its waiting list – but was told to fill in the paperwork and join the queue like everyone else. If she moved to a more affordable suburb in Sydney's greater west or south-west, she would have to uproot Maddison where he is settled in a special class at the local school and travel long distances to get to chemotherapy at Prince of Wales Hospital in Randwick. She would also lose proximity to her support network of friends while she struggles with cancer. She is now on a priority waiting list for community housing – a relatively small, private but not-for-profit sector in NSW. It could still take up to five years to get a home this way.

"I think we should be very careful about saying people poor people should live in the outer areas of Sydney and rich people should live in the nice areas close to the city," Wendy Hayhurst, the chief executive of the NSW Federation of Housing Associations Inc, said. The Federation represents community housing providers – which manage both social (low-income) and affordable homes - and is calling on the NSW government to adopt a city-wide strategic plan for affordable housing that addresses the crisis. NSW needed 100,000 new affordable homes in the next decade to keep up with demand, Ms Hayhurst said. "They [the government] are coming up with ideas, but not a strategy" she said. "When you've got a crisis you need to have an overall plan."

The market needed a signal from government in the form of targets to invest in the affordable sector, Ms Hayhurst said. "Rents have gone up and mortgages have gone up," she said. "10 years ago it was poor people who couldn't afford housing, whereas now it's up to people on moderate incomes." The sector is still waiting for the state government's response to a social housing discussion paper released a year ago. But Social Housing Minister, Brad Hazzard, has defended the government's record and pointed to plans at Macquarie Park and Glebe for low-income households. "NSW leads the country in new housing supply with 64,000 homes approved in the 12 months to September – the highest in almost 42 years," he said. "The supply line of housing is putting downward pressure on prices and we are now focussing on getting more social and affordable housing and reforming the social housing system to get the maximum use of taxpayer's assets."

The Social Housing Framework would be released in "coming months", he said. Meanwhile, the new mapping from City Futures research centre at the University of NSW shows affordability is being pushed to the outer suburbs of Sydney. Based on 2014 data, the report titled 'Housing affordability, central city economic productivity and the lower income labour market' will be published early next year.