There is no general minimum block size for a dual occupancy in RZ1 or RZ2 under the current ACT Missing Middle Housing rules.

Instead of relying on a minimum block size, whether two dwellings can be developed on a particular block depends on whether the proposal can meet the applicable planning and design requirements, such as site coverage, building height, setbacks, private open space, planting, parking and access.

This means a smaller block may potentially accommodate a dual occupancy if an appropriate compliant design can be achieved.

Reference: Planning (Missing Middle Housing) Design Guide 2026 – ACT Missing Middle Housing Design

Yes, 

The 2026 Technical Specifications changed how front setbacks are applied by removing separate lower and upper floor setback requirements and introducing a single dwelling setback requirement. The exact change depends on the applicable table, subdivision approval date, and type of frontage.

• Table 1 (corner blocks – secondary street frontage): Under the 2025 specifications, a large block required a 4 m setback for the lower floor and 6 m for the upper floor to the secondary street frontage. The 2026 specifications remove this distinction and require a single 4 m setback for the dwelling, regardless of storeys. The 6 m garage or carport setback remains unchanged.
• Table 2 (subdivisions approved on or after 18 October 1993 but before 31 March 2008): Under the 2025 specifications, a large block required 4 m for the lower floor and 6 m for the upper floor for both the primary front boundary and secondary street frontage. The 2026 specifications replace this with a single dwelling setback of 4 m for both the primary front boundary and secondary street frontage. Garage and carport setbacks remain unchanged at 5.5 m.
• Table 3 (subdivisions approved on or after 31 March 2008): Under the 2025 specifications, a large block required 4 m for the lower floor and 6 m for the upper floor to the primary front boundary. The secondary street frontage setback remained 3 m, and the public open space or pedestrian path setback remained 4 m. Under the 2026 specifications, these are replaced with a single dwelling setback of 4 m to the primary front boundary, 3 m to the secondary street frontage, and 4 m to public open space or pedestrian paths wider than 6 m, regardless of storeys. Garage and carport setbacks remain unchanged.

• Table 4 (Multi-unit housing front boundary setbacks): Under the 2025 Technical Specifications, front setback requirements were separated into lower floor and upper floor levels. For subdivisions approved on or after 18 October 1993, the primary front boundary setback was 4 m for lower floors and 6 m for upper floors, with garages and carports set back 5.5 m (including at least 1.5 m behind the front building line). Older subdivisions required a 6 m setback. Secondary street frontage and pedestrian path/public open space setbacks also varied depending on the frontage type and block size.

  Under the 2026 Technical Specifications, these requirements are simplified by removing the lower and upper floor distinction. A single dwelling setback now applies:

• Primary front boundary: 4 m for subdivisions approved on or after 18 October 1993, and 6 m for earlier subdivisions.
• Secondary street frontage: 2 m for corner blocks.
• Pedestrian paths up to 6 m wide: 3 m.
• Public open space or pedestrian paths wider than 6 m: 4 m.
• Garage and carport setbacks remain unchanged, including the 5.5 m setback for newer subdivisions and the applicable setbacks for other frontage types.

The updated requirements should be checked against the relevant front boundary setback table in the Planning (Residential Zones) Technical Specifications 2026, as the applicable requirement depends on the block circumstances.

Reference: Planning (Residential Zones) Technical Specifications 2026 (NI2026-303), Assessment Outcome 14.5- Planning (Residential Zones) Technical Specifications 2026

The minimum planting area for single dwellings has not changed. A large block must have 30% of its area as planting space, a mid-sized block needs 20%, and a compact block needs 15%. Any area counted as planting space must be at least 2.5 metres wide and cannot include structures such as retaining walls, water tanks, hot water systems, or air-conditioning units. Artificial turf is not allowed in the required planting area, which must be made up of real landscaping and plants.

Reference: Planning (Residential Zones) Technical Specifications 2026 (NI2026-303) – Assessment Outcome 19.1 – Planning (Residential Zones) Technical Specifications 2026

There is no general rule saying that a block must be rectangular. However, its shape can influence where and how much you can build.

For example, on a triangular or irregular block, the side boundaries may converge toward the rear. Once the required setbacks are applied, the resulting buildable area may become narrower, which can affect the size, position and layout of the proposed dwelling.

Similarly, a narrow block may make it more difficult to accommodate a driveway, parking, planting and private open space while still meeting the required building setbacks.

The important point is that block shape itself is not necessarily a restriction; it is how that shape interacts with the applicable planning controls that determines the development potential.

Reference: Planning (Residential Zones) Technical Specifications 2026 (NI2026-30) – Planning (Residential Zones) Technical Specifications 2026 | PDF