Australia's homelessness figures are going in the wrong direction, and housing experts warn we're about to recommit to a failing policy.

Key points: Almost 50pc increase in Sydney, around 30pc increase in Darwin and Brisbane

Almost 50pc increase in Sydney, around 30pc increase in Darwin and Brisbane Rough sleeping has gone up by 20pc since 2011

Rough sleeping has gone up by 20pc since 2011 Experts say there has not been enough investment in low cost housing

Last month's census data revealed that after a long period of stability, homelessness in Australia has gone up 14 per cent nationally, in the past five years.

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In Sydney, there has been an increase of almost 50 per cent, while Darwin and Brisbane both saw increases of around 30 per cent.

Rough sleeping — a term which refers to living outside or in a car — has gone up by 20 per cent since 2011.

That is despite the fact more than $9 billion has been spent since 2009 through the National Affordable Housing Agreement.

The Federal Government and the state are currently in the process of trying to renegotiate the deal, with a slightly different name, by next month.

The new National Housing and Homelessness Agreement (NHHA) would lock in $4.6 billion in funding for states and territories over the next three years, but so far the states have been reluctant to sign on.

Plenty of policy experts are also warning it will not solve Australia's homelessness problem.

Hal Pawson, professor of housing policy at the University of New South Wales, said the NAHA was more of a, "device that enables the status quo to be preserved".

He argued the new agreement was essentially an extension of that.

Kate Colvin, spokeswoman for the Everybody's Home campaign, which represents the community sector housing and homelessness groups, said the NHHA would not change anything.

"Because the fundamental problem is that there's not an adequate subsidy to get more low-cost housing on the ground," she said.

"There's just not enough low-cost places that people can afford to rent."

Economist Saul Eslake said there was no extra money in the rebranded funding agreement, and no change in how its success was measured.

"It would seem that they've been unable to reach agreement with the states and territories on this, so there won't be much improvement in the way in which states' and territories' performance is benchmarked," he said.

'It could happen to any of us, at any time'

Rima Israel and her son have somewhere to live at the moment, but they have been without a home, on and off, for a decade.

"I was 29, I was an area manager for fast food, so I actually had a very good career where I could afford to pay and I did pay private rent for years," Ms Israel said.

"But I had a domestic violence relationship and I had to leave everything.

Rima Israel and her son have been without a home, on and off, for a decade. ( ABC News: Flint Duxfield )

"After that, I moved back in with my parents for a little bit of time but it was always constant arguing, so I moved from couch to couch with my friends, trying to look for a job, and then I fell pregnant."

It took six years before Ms Israel was accepted into social housing.

"They said, 'No, sorry, you earn too much on Centrelink. So you can afford to rent at this price'," she said.

She was rejected from more than 50 properties.

"I couldn't find anything in the price they had said to me that I could afford," Ms Israel said.

Rima Israel said there are a lot of roads that lead to homelessness.

"Death in the family, loss of job … it could happen to any of us, at any time," she said.

"And if we don't start to do something about it now, the situation's only going to get worse."

So what are we doing wrong?

Policy experts agree one of the main culprits pushing up homelessness is the housing affordability crisis.

Mr Eslake said people like Ms Israel who need affordable rentals, have too much competition.

"We've had pressure on both the demand and the supply sides of Australia's housing markets," he said.

"That in turn has increased the competition that low-income households face seeking to get rental accommodation at rents they can afford."

A parallel shortage of social housing has meant those who have been pushed out of the lower end of the rental market have nowhere to go.

Mr Eslake blamed a lack of investment.

"Apart from a period in 2010 through 2012 … the amount of money that has been provided by successive [federal] governments to the states, for the construction of new affordable social housing, has declined over time," he said.

Professor Pawson said the downward trend was established back in the 1990s.

"Historically, a chunk of that money was designated to help the states and territories actually, year by year expand their public housing stock," he said.

"It was to help increase supply. After 1996 that stopped."

Mr Eslake has a theory as to why growth in social housing has dried up — there are simply no votes in it.

"The Coalition thinks that social housing is predominantly located in safe Labor seats, and people who require social housing … are traditionally left-of-centre voters," he said.

"The Labor Party also regards the votes of people living in social housing as more or less locked in.