Minister for Housing Andrew Barr said the government was reviewing an independent evaluation of the 2014 rental market before making changes to rent in public housing, with tenants requiring a minimum of 8 weeks' notice before any alteration.

Mr Barr said there had been a wide variability in the rental market during the past 12 months with changes often dictated by the location, size, and standard of the property.

"If the market rent decreased over the year, the market rent for an equivalent public housing property is also likely to decrease," he said.

ACT Housing rent had not been altered since mid-2013, Mr Barr said, as the government only makes changes 12 months after a previous revision to ensure the "ease of efficiency in managing the public housing portfolio".

"The 2013 market rent review was applied to tenants' rent accounts on July 21 2013 and therefore the earliest date that the 2014 market rent review could have been applied was July 27," he said.

But the rental market in Canberra has changed significantly since July 2013 with economists warning the downward trend in rental prices may be likely to continue.

According to June quarter figures released by Australian Property Monitors, the median weekly rent for houses in the ACT fell by 6.3 per cent to $450.

The average weekly rent for units in Canberra fell by 6.1 per cent to $385, which meant units transitioned from being the third most expensive in the country during April to among the cheapest.

Australian Property Monitors Domain Group senior economist Andrew Wilson believes Canberra's rental woes were due to subdued housing conditions that may continue to exist for some time.

"There's a consistency about the fall over the year for both houses and units, and I do think it's just generally a lack of demand for rental properties in Canberra," he said.

An ACT Tenants Union spokeswoman said she expected the government to make a decision on public housing rent by early October but expressed some frustration with the annual review.

"From a practical point of view, doing a review for each property when a new individual tenancy starts is neither practical nor workable," she said.

"But the problem with doing it in bulk is there's isn't a person going out to each property to assess the individual rent situation."

The ACT Tenants Union spokeswoman agreed with Mr Barr that the majority of tenants in ACT Housing were unlikely to pay market rates with 95 per cent of tenants in receipt of a rental rebate.

"Their rent payable is based upon a maximum of 25 per cent of their income, [although] most pay even less than this due to various income exemptions," Mr Barr said.

Once notified of any changes to rent in ACT Housing, a tenant can contest the decision with the Commissioner for Social Housing or the ACT Civil and Administrative Tribunal.

"Upon receipt of that notice, tenants can apply to Housing for an independent review of the rent," Mr Barr said.

"Tenants not happy with the Commissioner's decision or the independent review can lodge an appeal to the ACT Civil and Administrative Tribunal for a review of the rent."

The ACT Government's review of public housing rent comes at a time the proportion of public housing in the ACT has fallen to the lowest levels since self-government, according to data obtained under freedom of information laws.

In 1991, the proportion of public housing for a city with 280,132 people was 11.91 per cent. In 2011, the proportion had fallen to 7.8 per cent for a population of 328,586 and separate government figures show, in 2014, a further decline to 7 per cent.

- with Meredith Clisby