Separately titled dwellings will be permitted on all larger blocks across Canberra's suburbs as part of the biggest shake up to the city's planning system since self-government.
The changes will apply to almost 45,000 blocks across the capital.
A second dwelling up to 120 square metres will be allowed on any block in an RZ1 zone over 800 square metres, with rules to govern tree coverage and soft landscaping requirements.
The rule change will make it easier to build second dwellings on a large number of blocks in Canberra's older and established areas, in a move the government expects will improve housing supply.
Planning minister Mick Gentleman said that the aim was to increase the supply of housing in Canberra "but keep it as an attractive place to live".
He said neighbours of people who wanted to build a second dwelling on a block would be able to have a say in the development application process.
He later said on local radio that the changes would give Canberrans a chance to downsize without moving - in other words, by building a smaller dwelling (in which to downsize) on their existing block.
Mr Gentleman said the changes would not alter the commitment to the number of trees.
The government is on Monday set to release district strategies, the territory plan and design guides needed to implement its overhauled planning system.
Chief Minister Andrew Barr said the documents would reflect the ACT government's commitment to the national housing accord and the planning reform blueprint agreed to by state and territory leaders at national cabinet.
"Canberrans would have seen how this type of reform can increase housing supply in their suburb through the Mr Fluffy buyback scheme. This experience demonstrated that with the right protections in place - we can add suitable housing in existing suburbs," Mr Barr said.
Tuggeranong has 14,009 RZ1 blocks larger than 800 square metres, with 11,833 blocks in Belconnen, 7462 blocks in Canberra Central and 5242 in the Woden Valley.
Gungahlin has 2181, Weston Creek has 3923 and the Molonglo Valley has 83.
The blocks will be eligible unit-titled dual occupancies as long as dwelling size and other planning requirements can be met.
Mr Barr had foreshadowed the changes last week, but had not spelled out the detail of what would change in the RZ1 zone.
The Mr Fluffy rules, which applied only applied to blocks cleared as part of the loose-fill asbestos insulation buy-back scheme, permitted unit-titled dual occupancy developments if the site was more than 700 square metres in zone.
The new dual occupancy rules are expected to have tighter rules governing tree coverage, soft landscaping and site coverage than the Mr Fluffy scheme.
A 2017 government discussion paper said more than half of Canberrans surveyed wanted more dual occupancies in their area. At the time, RZ1 rules covered more than 80 per cent of Canberra's residential land.
Dual occupancies on 800 square metre blocks currently do not allow the titles to be separated, meaning the properties must be sold together.
Mr Barr in March said there was merit in expanding the Mr Fluffy dual occupancy rules as part of the planning system changes, in an effort to deliver more housing in established suburbs close to employment and other facilities.
"There's a way to do this that would address legitimate concerns about neighbourhoods changing dramatically, but at the same time offer more product and a house size that's 100 to 150 square metres, so equivalent to a three-bedroom apartment probably, but at a single level, in a gentle transformation of some of the larger blocks in places where people want to live," Mr Barr said at the time.
The current objectives for the RZ1 zone include protecting "the character of established single dwelling housing areas by limiting the extent of change that can occur particularly with regard to the original pattern of subdivision and the density of dwellings".
ACT Labor amended its policy platform at its annual party conference in July to endorse overhauling the RZ1 zone to allow medium density housing in line with what is already permitted in RZ2.
New planning laws, which will significantly recast the way the ACT's planners consider proposed developments, passed the Legislative Assembly in June, following a detailed debate.
