Three houses accommodating 15 people will be built across the city for patients who are capable of living in the community but require ongoing support because of persistent mental illness.

Mental Health Minister Shane Rattenbury said it was about having a spectrum of support services across the territory to provide the right care at the right time, in the right place.

The funding will go both towards building new supported accommodation facilities and running them.

The extra 15 rehabilitation beds - to provide 24-hour supported accommodation for people with complex mental health needs - will add to the 20 mental health rehabilitation services soon to open at the University of Canberra Hospital and the existing 94 community based residential beds across the territory.

Mr Rattenbury said there would also be extra funding for a Step-Up-Step-Down facility on the south side of Canberra to provide post-hospital care and money for the refurbishment of the 10-bed extended care unit at the Brian Hennessey Rehabilitation Centre.

Executive director of ACT mental health Katrina Bracher said the sector was experiencing a huge increase in demand.

"This is an initiative we've been working with the government on for a number of years to have some supported accommodation options to use for patients within the community," she said.

"Without a doubt our service system is under a level of pressure.

"The growth in mental health demand is documented in our community.

"Our services are responding to that demand too."

Mr Rattenbury said the investment in mental health accommodation and support services would significantly boost the frontline care Canberrans could access.

“By investing $22.8 million in supported accommodation, we are delivering greater support both for people experiencing severe mental health episodes and those managing chronic conditions," he said.

“Around one third of Canberrans will need mental health care at some stage in their lives. This means that our local services and facilities have to expand as our population grows so that people can access the right care when they need it."

This funding comprises $12.2 million for infrastructure costs and a further $10.7 million to manage and run the facilities.

But no funding has yet been allocated to the acute mental health wards, which have come under increasing strain in the face of overwhelming demand.

The most recent available statistics from the productivity commission show demand for ACT's acute mental health beds has grown by 50 per cent since 2006/07, while it has remained mostly stable across the country.

The statistics show there have been just three extra acute beds added in the same time frame.

They do not account for the Dhulwa mental health unit - which cares for mental health patients involved in the criminal justice system - which opened 10 secure acute mental health beds.