Surging inmate numbers have forced the government to prepare a second full-time prison to take overflow from the Alexander Maconochie Centre, where overcrowding is again reaching breaking point.
The ACT's prison, opened in 2009, has been under pressure from a rapidly increasing detainee population since 2013.
To cope, a temporary expansion has increased capacity from 332 beds to about 370, while an urgent and major permanent upgrade was launched to add an extra 110 beds by mid-2016, with the first 30 to be ready by the second half of this year.
But, despite those efforts, overcrowding has recently reached critical levels again at the AMC, consistently at 350 detainees or above.
That has forced Justice Minister Shane Rattenbury to spend $60,000 upgrading the Symonston Correctional Facility - currently used for weekend detention - for use as a temporary full-time prison, to be opened when needed and otherwise closed.
It is now ready to take overflow from the AMC when numbers increase, and can house a maximum of about 22 prisoners full-time, in addition to those already serving weekend detention at the Periodic Detention Centre.
It is expected to be closed when permanent upgrades to the AMC are complete.
The decision is likely to raise questions on a number of fronts; whether the much-older Symonston facility is properly secured, how much it will cost, how it will be staffed, and whether it will be human rights compliant, given its comparative lack of services and facilities.
Mr Rattenbury said the Symonston facility - which sits on Mugga Lane close to residential areas in Narrabundah, Griffith and Red Hill - has been significantly upgraded and is now suitable for use as a fully secure full-time prison.
All inmates to be sent to the overflow facility will be assessed for suitability. Only the most compliant and lowest risk prisoners will be approved for Symonston.
"We don't want people up there who are problematic," Mr Rattenbury said.
"We have a range of detainees who are very compliant, who are very easy to manage, and they're the ones we are targeting for Symonston," he said.
It will cost the government an extra $100,000 a month to run the facility, and Mr Rattenbury said current staffing levels would be enough to run the two prisons.
The Symonston centre has been in use for about 20 years, as a weekend detention centre and at one-time as a full-time remand centre that helped alleviate pressure on the overcrowded Belconnen Remand Centre.
Both remand centres were audited by the Human Rights Commission in 2007, and were criticised in a range of areas, including for allowing little time out of cells and for excessive lockdowns.
The Symonston building is without a proper health centre or library, and prison-based programs, such as drug and alcohol rehabilitation, will not be available.
To ensure human rights compliance, Mr Rattenbury said the health centre staff based at the AMC will visit Symonston, or detainees will be transferred to receive care.
No prisoners will be removed to Symonston if they are enrolled in a program at the AMC, and library access will be facilitated if required.
The Human Rights Commissioner and Official Visitor will both be granted full access to the second prison.
There is currently no operational start date for the new Symonston facility.
It is ready for use but will only be activated when necessary.
Letters were sent to residents of Red Hill, Griffith, and Narrabundah on Wednesday to inform them of the changes.
Mr Rattenbury said residents were unlikely to notice any real difference, given the Symonston facility was already holding weekend detainees.
Fairfax Media revealed in 2013 that the government had been warned in 2001 that prisoner numbers would reach levels that would quickly overcrowd a 332-bed facility.
But it buried the advice, provided by consultant John Walker, and instead used its own, lower prisoner projections to justify a smaller and cheaper facility.
Weekend detention is being phased out by 2016-17 and the Periodic Detention Centre is due to close once the last of the part-time detainees have served their sentences.