Corrections Minister Shane Rattenbury on Wednesday toured the new Alexander Maconochie Centre building for inmates who needed in-house rehabilitation programs for behavioural problems and drug addiction.

The unit is the first stage of a $54 million expansion project that will boost accommodation at the jail by 110 beds with additional surge capacity.

Mr Rattenbury said the facility would provide some short-term relief from the jail's "intense accommodation pressures" until the neighbouring 56-cell block significantly eased demand on the existing facilities mid-next year.

It comes as a temporary Symonston overflow facility renovated to take up to 30 prisoners from the main jail has consistently been close to full in recent months.

The number of detainees in the ACT has hovered around 373 in recent weeks. The expansion's two buildings will increase the jail's capacity to 512.

Close to 30 detainees are expected to move into the new unit in coming days.

Mr Rattenbury said the new buildings would provide greater segregation options to distance troublesome offenders, many of whom knew each other, and reduce tensions between inmates.

"It has been one of the key operating lessons since the AMC opened, that our necessary separation rates are higher than other jurisdictions being the only jail here in the ACT, a small town.

"The new structure of the accommodation here at the AMC will overcome the fact we don't have another jail to send them to, but we will have another area within the AMC to send them to."

"The design of this building and the building next door will allows us that greater degree of separation which will improve management at the jail as well."

The new unit features three separate wings that include cells, interview and program rooms, a central office for staff and kitchen and recreation spaces.

There are wheelchair friendly cells and capacity to add a double-bunk to each room.

Custodial operations general manager Don Taylor said services, health professionals and psychologists would be housed within the unit so detainees didn't need to be mixed and moved around the centre to access services.

"At the moment the centre's been built so all our detainees have to go through one area to get to the programs room, the health centre, the education centre.

"Having the detainees able to have those services provided in the unit just creates a lot less movement within the centre."

Mr Taylor said it would be the first time staff could house detainees in different sections according to their individual needs.

Corrections staff will assess detainees at the main jail and the temporary Symonston facility in coming days to decide which inmates will move to the new unit.