Corrections is insisting it has no choice but to double bunk women in tiny cells at Arohata's overflow prison at Rimutaka despite scathing criticism from the Chief Ombudsman.
The Department says a huge and rapid rise in the number of women being locked up means there's not much else it can do.
The cells at Arohata Upper Prison are being described as not fit for one person let alone two.
International standards set the minimum size for a single cell at six square metres with additional room for a toilet.
The ones at the Arohata overflow are slightly smaller than that and include the toilet.
The Ombudsman Peter Boshier said the situation was unacceptable.
"They're sharing cells which in the old days were barely adequate, international standards they are not up to size and when you're double bunking they're probably half the required size, so you'll see that we're forcing a situation which is unacceptable."
The female prison population has gone up by 40 percent in the past two years, forcing Corrections to re-open Arohata's satellite prison which had closed in 2015.
In May last year, two of the four prison wings were being used - by September all four were open.
The number of inmates is still going up and the department's Neil Beales said double-bunking was the only option.
"We have to take prisoners from the courts, we can't turn them away at the gates because we don't have any space, so we recognise that the Ombudsman was concerned about that, but equally where do we put the prisoners? We can't put female prisoners in a male prison."
After consultation with the Ombudsman and unions Corrections cut the number of planned double-bunked cells from 88 to 44.
The pressure will ease a bit when the main women's prison in Wellington is expanded to take on 69 more prisoners by the middle of next year.
Neil Beales said new facilities at Auckland Prison would also help but they wouldn't be open until later this year, Mr Beales said.
"But until they are built, until we have them installed, we've got to manage the prisoners coming through the gate.
"We can't turn them away, we can't tell the courts to stop sentencing prisoners - that's not our role. Our role under regulations and the legislation is to safely manage prisoners who come to us."
The Corrections Department has said it will give the women's units at Rimutaka a $10 million facelift which will include two new yards and improved gym facilities in response to the Ombudsman's report.
Human rights lawyer Michael Bott said the double bunking plan was hideous, but not surprising.
"Under the last government especially you saw a massive increase in the prison population to record numbers that had never been reached before and this is an outworking of that."
The Ombudsman's report on Arohata Upper Prison also found that the cells were cold and austere with little natural light.
Although the women were low security they were treated more like high security with 15 hour lock-up times that often meant they couldn't ring their children after school, the report said.
Prisoner misconduct was increasing as the number of inmates rises, it said.
Mr Bott said double-bunking would only make things worse.
"Arguably the more draconian and harsh you make a prison environment, you actually psychologically damage a person, they become unmotivated, because of the absence of daylight they often can become depressed, psychiatrically disturbed, or even more so than when they went in."
Double bunking would be considered cruel treatment under the Bill of Rights Act, and should be banned, he said.