My block is under 600 m² — can I still add a second home bigger than 90 m²?
This is where the dual-occupancy pathway is particularly relevant for a smaller block.
A second dwelling is not automatically restricted to 90 m² just because the block is below 600 m². The current pathways are different:
- Secondary residence ? maximum 90 m² and cannot subsequently be subdivided or unit titled.
- Dual occupancy ? no minimum block size under the current Missing Middle framework and no specific maximum dwelling-size cap of the kind that previously applied. The actual size that can be achieved is instead controlled by the overall planning and design requirements applying to the site.
So, for example, a 550 m² block could potentially accommodate a dual occupancy with the second dwelling exceeding 90 m², even though the block may not qualify for the same subdivision or titling options as a larger block.
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
Yes. If you are proposing a dual occupancy, a block under 600 m² can still potentially accommodate a second dwelling larger than 90 m².
Under the Missing Middle Housing reforms that commenced on 1 July 2026, dual occupancy has no minimum block-size requirement and the former maximum dwelling-size restriction has been removed. The Missing Middle Housing Design Guide identifies “No minimum” block size for dual occupancy.
Detailed Explanation
The Missing Middle Housing Reforms (MPA-04) changed the Territory Plan from 1 July 2026 to remove barriers to multi-occupancy housing in RZ1 and RZ2. ACT Planning confirms that the amended Territory Plan now enables missing-middle housing—including duplexes/dual occupancies—across these zones.
The current Missing Middle Housing Design Guide's site-scenario matrix identifies the block-size guide for Dual Occupancy as “No minimum.”
Accordingly, 600 m² should not be used as the minimum block size for constructing a dual occupancy, nor should a second dual-occupancy dwelling be subjected to the 90 m² secondary-residence limit. Instead, the achievable dwelling size is determined by the combined applicable controls, including site coverage, setbacks, building envelope, planting, private open space, parking, access and other relevant Territory Plan requirements.
No minimum block size does not remove the need for planning assessment.
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