The latest figures from the Productivity Commission's Report on Government Services show nearly half (47.8 per cent) of low income households in the ACT experienced rental stress in the last year.

Rental stress is defined as households spending more than 30 per cent of their income on rent.

Nearly half (48 per cent) of ACT households receiving Commonwealth rent assistance - the largest government private rental assistance program in the country - were still experiencing rental stress after they received their payment.

Without that payment, more than 70 per cent of those households would have experienced rental stress.

One in five (21.9 per cent) private renters with rent assistance were still paying more than half their income to their landlord, even with the payment.

That rose to 35.6 per cent without the payment.

Almost 85 per cent of ACT households receiving rent assistance were paying enough rent to be eligible for maximum assistance, the highest in Australia.

More than 11,000 ACT households received Commonwealth rent assistance last financial year.

Of those, 17.8 per cent were students, 16.5 per cent were receiving Newstart payments, 15.9 per cent were on the disability support pension and 12 per cent were on the aged pension.

Family tax benefit claimants accounted for 22.4 per cent of ACT households receiving rent assistance.

More than 22 per cent of ACT recipients were aged 24 and under, the highest percentage in the country.

A whopping 72.2 per cent of the households still in rental stress even after receiving rent assistance included a member aged under 24 years.

Of households paying more than 50 per cent of their rent in income, 44.1 per cent had a member aged under 24.

The federal government spent $4.4 billion on Commonwealth Rent Assistance in 2016‑17.

$34.7 million of that was in the ACT.

The report said in the ACT 63.2 homes were built per 1000 low and moderate income households that should be affordable, a rate nearly three times higher than NSW and far higher than anywhere else in Australia.

But Domain figures showed the median cost of renting a house in Canberra was $540 a week in December, up from $500 a year earlier.

This made Canberra the third most expensive capital city in which to rent in Australia.

The ACT Greens housing spokeswoman Caroline Le Couteur said more needed to be done in the ACT to fix the "ever-more unaffordable" private rental market.

"The market is caught in three directions - for the poorest people in our community, the lack of public and community housing options can lead to homelessness, and place added pressure on already under-resourced crisis accommodation services," Ms Le Couteur said.

"For those further up the housing ladder, many of whom have low-paying jobs, there are not enough affordable rentals available. Others who would otherwise buy, such as young professionals, are priced out of the overheated market.

"It's not acceptable that in a jurisdiction as fortunate as ours that, as reported in the media today, almost one in three Canberrans seeking accommodation assistance in 2016-2017 weren't able to find a safe housing option.

"If we're to adequately address housing shortages in the ACT, the Government must set strong, ambitious targets for public, community and affordable housing."

Housing targers are part of the Greens' powersharing deal with the Greens, and Ms Le Couteur said the ACT government needed to do more to strengthen homelessness services, and review key planning rules and levers.

"The ACT Greens also support ACTCOSS' recent call to divert $100 million from the current ACT Government bonds to create an investment fund for community housing providers for the purpose of building new accessible, affordable rental housing. The fund would be held in perpetuity and repaid at government bond rates," Ms Le Couteur said.

"However, most importantly, the government must first act urgently increase the supply of affordable rentals and public and community housing."