Why would I choose multiple occupancy over a granny flat?
The main difference is size and standing.
A granny flat / secondary residence is intended to be a smaller home associated with the main dwelling. It is limited to 90 m² and cannot later be separately subdivided or unit titled. ACT Planning expressly states that a block containing a principal dwelling and secondary residence cannot be subdivided under the Planning Act 2023 or Unit Titles Act 2001.
A multiple occupancy, such as a dual occupancy, treats the proposal as a multi-dwelling development rather than one principal home with a subordinate secondary residence. Under the current Missing Middle framework, the Design Guide identifies no minimum block-size guide for dual occupancy, and the current reforms enable missing-middle housing across RZ1 and RZ2.
So, if 90 m² is enough, a secondary residence may be the more straightforward option. If you want a larger and more independent second home, dual occupancy may provide the better pathway.
Reference: Planning (Missing Middle Housing) Design Guide 2026 (NI2026-312) – https://www.planning.act.gov.au/__data/assets/pdf_file/0020/3092411/ACT-Missing-Middle-Housing-Design-Guide.pdf
Short Answer
Choose multiple occupancy (such as a dual occupancy) when you want the second dwelling to function as a more substantial, independent home, particularly where the 90 m² secondary-residence limit is too restrictive.
A secondary residence (often called a granny flat) can be a simpler option for a smaller additional home, but it remains subordinate to the principal dwelling and is subject to the 90 m² maximum dwelling size. Multiple occupancy provides greater flexibility for a full-sized second dwelling, subject to the applicable planning and design requirements.
Detailed Explanation
The two pathways represent different development types and should not be treated simply as different names for a second dwelling.
A secondary residence remains associated with single-dwelling housing and is subordinate to the principal dwelling. It is subject to the applicable secondary-residence requirements, including the 90 m² dwelling-size limit, and ACT Planning confirms that a block containing a primary dwelling and secondary residence cannot subsequently be subdivided or unit titled.
A dual occupancy falls within the current Missing Middle multi-occupancy housing framework. The Missing Middle Housing Design Guide applies to residential proposals of three storeys or less providing more than one dwelling, while the 2026 Territory Plan amendments expanded missing-middle housing opportunities across RZ1 and RZ2.
No minimum block size does not remove the need for planning assessment.
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