The study, commissioned by the ACT government and released on Tuesday, found that a lack of affordable housing in Canberra's notoriously expensive rental market was clogging up crisis accommodation, leaving some lingering in shelters for months on end while others couldn't get a bed at all.

Workers told researchers at the University of Queensland of families sleeping in their cars or hospitals discharging patients with just a swag because there was nothing for them.

"Everything is chock-a-block full at the moment," one worker said.

Clients said some options offered weren't safe, particularly for women, describing complexes where drug use was rampant and privacy minimal.

Drawing on data between 2011 and 2017, the study found that on average almost two thirds of the people fronting up to ACT services each year were already homeless, while 38 per cent were at risk.

About 383 or 10 per cent of them had high and complex needs such as medical or mental health issues, drug or alcohol dependence or a history in state care. While those falling into this category were more likely to be male and single, the number of women with complex needs rose over the six year period. The total identified as homeless with complex needs fell slightly in that time.

The study suggested a rethink of the traditional "staircase" model that usually saw housing offered with conditions. Pushing people with complex needs through bureaucratic hoops to demonstrate their "housing readiness" could trap them in homelessness even longer. Instead, researchers called for more permanent supported accommodation, where housing and support were delivered by separate providers, and clients could be fast-tracked into homes.

Housing Minister Yvette Berry said she was committed to plugging gaps in the system. To that end, the government will spend millions to build more public housing and boost front line services over the next few years. But it has so far resisted calls from some parts of the sector for a year-round crisis shelter as it looks to longer-term options.

At Safe Shelter, which opens Canberra churches and halls for men to sleep during winter, Richard Griffiths warned not enough was being done for people living on the street in the meantime.

Revealing demand at the shelter had again doubled from last year, Mr Grifftths called for a "genuine public inquiry" to help map Canberra's homelessness population, often missed in statistics.

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Based off the latest ABS census data, the ACT's estimated rate of homelessness fell by about 8 per cent between 2011 and 2016. But the number of people counted as rough sleepers on census night almost doubled.

"[Our figures] show the ACT has a growing homeless population, as can be seen around shopping centres - not just beggars, but rough sleepers," Mr Griffiths said.

Volunteers had had to turn away six men, one woman and a mother with two children from the shelter already this winter.

But of the 49 men who had been put up for the night so far, 37 had stayed for less than a week, suggesting most found another option.

"[Our] volunteers can claim some credit for making that possible," Mr Griffiths said.

Travis Gilbert at ACT Shelter sat on the community reference group for the study and said, while its findings were important, its scope appeared quite limited.

"They don't appear to have spoken to many people actually in that situation, mostly service providers, and that's not a fault of researchers but I think more work needs to be done around what these people actually want for their future housing needs," he said.

The researchers also advised caution when analysing the data, as real populations were likely greater than those supported by services.

Mr Gilbert said the territory was investing more than most jurisdictions in its public housing stock but its comparatively small population size gave it less of a share in Commonwealth funding.

"A true housing first approach is going to take serious investment from the ACT in the bricks and mortar," he said.

"We have to be careful we're not using the words 'housing first' without the homes to back it up."

Mr Gilbert said the ACT's $100 million investment in public housing was still only around a seventh of its annual revenue in property tax.

"I understand [what's needed] would be huge but the savings in health [and justice] will be huge too," he said.

"A stay in Canberra Hospital costs about $6000 a night, supported accommodation is nothing near that but we know people sleeping rough will be checked into emergency about five, six times a year."