Granny flats and dual occupancies in the ACT after the Missing Middle reforms

What did the Missing Middle reforms change?

Since 1 July 2026, ACT planning rules allow more homes on ordinary suburban blocks. RZ1 now allows "duplexes, triplexes, terrace homes, townhouses and low-rise apartments of up to two storeys", and RZ2 allows the same up to three storeys.

The change came in as Major Plan Amendment 04 (MPA 04) to the Territory Plan, better known as the Missing Middle Housing reforms. Four parts of it matter most if you're thinking about a second home on your block:

• More housing types in RZ1 and RZ2, as above.
• Subdivide first: RZ1 blocks can be subdivided "without first building a dwelling, provided minimum block sizes are met". We haven't checked the new minimum sizes, so we don't quote one.
• No block size threshold for granny flats: MPA 04 removed the "minimum block size thresholds that previously limited secondary residences".
• Site coverage for multi-unit housing: 45% of the original block in RZ1 and RZ2.

That last figure is pre-reform context: a Minister's answer to a Legislative Assembly question put RZ1 dual occupancy applications at 36 over those seven months. Whatever the new rules allow, the approvals and the engineering still apply.

What are the granny flat rules in the ACT?

A granny flat in the ACT can be up to 90 m², one per block, up to two storeys, and only alongside single dwelling housing. The Territory Plan calls it a secondary residence, and its rules sit in the residential zones policy (E01), in effect from 1 July 2026.

Territory Plan 2023, E01 Residential Zones Policy, from 1 July 2026; Missing Middle Snapshot 2026.

Two details catch people out. The 90 m² is measured to the outside of the walls, so the floor area you can actually use inside is smaller. And a garage isn't counted, so a garage beside the granny flat doesn't eat into the 90 m².

Do you still need a lease variation for a granny flat?

Possibly not for much longer, but don't plan on it yet. The Planning (Missing Middle Housing) Amendment Bill 2026 would let secondary residences be built on single-dwelling leases without a lease variation. It also sets up a 10 working day pathway for lease variations.

The bill passed on 21 October 2026. On 6 November 2026 the ACT Legislation Register showed it as passed and awaiting notification, so it was not yet in force when we wrote this. It starts the day after it is notified. Check its status on the register, or ask your designer or certifier, before you budget around it.

Which approvals does a granny flat or dual occupancy need?

A second dwelling needs both development approval (DA) and building approval (BA). In the ACT the DA comes from the Territory Planning Authority, and the BA from a licensed certifier you appoint.

Development approval

Exempt work must not take a block to two or more dwellings. That rule is part of the general test for every DA exemption, so a granny flat or dual occupancy is never DA-exempt under it. Plan for a DA.

Building approval

The ACT says "there are no BA exemptions for detached houses (defined as class 1 buildings)". A second home is a dwelling in its own right, so plan for a BA. Your certifier inspects the footings before the concrete is poured and the frame before it is lined. The Construction Occupations Registrar then issues the certificate of occupancy and use, and it is against the law to live in the building before that.

If the project also alters the main house and that house was built or started before 1985, the BA application needs an asbestos removal control plan. Our guide to older homes and asbestos in the ACT covers it.

Site coverage

Site coverage limits how much of the block buildings can cover. The house and the granny flat count together.

Territory Plan E01, rules 7 and 8. Your designer confirms which category your block falls into. Storey limits: two in RZ1, three for multi-unit housing in RZ2.

What else applies to Missing Middle projects?

Three more rules shape a second home or a small multi-unit project: no gas, a developer licence from three dwellings, and a choice of building code until April 2027.

• All-electric. The Territory Plan says "no new gas network connections are allowed to all new or existing developments including redevelopments". A new granny flat or duplex is all-electric.
• Property developer licence. Since 1 October 2026 a licence is needed for projects of three or more dwellings, and from 1 April 2027 to sell off-the-plan. The Registrar can order serious defects fixed up to 10 years after completion. A house plus a granny flat is two dwellings; a triplex is three, so check whether the licence applies to you.
• Building code. Building approvals from 1 May 2026 to 30 April 2027 can use NCC 2022 or NCC 2025, with the matching ACT Appendix, but not a mix. NCC 2025 becomes mandatory on 1 May 2027, except for projects with a DA lodged before 1 November 2026.

What engineering does a granny flat or dual occupancy need?

Most second dwellings need footing and slab design, framing and tie-down details, and often retaining or design around a sewer main. The certifier can't lodge the BA without the structural details.

Footings and slab for your site's soil

The ACT's minimum documents for house BAs (form AF2025-18) include footing and slab details with the "nominated founding depth and description of founding material", plus reinforcement and concrete strength. No ACT document names a geotechnical report, but the footing design has to suit your site's soil. When a soil test is needed we arrange it and pass on its cost. Footing and slab design and site classification starts at $1,290 + GST ($1,419 inc GST).

Ground changes across Canberra. In parts of Gungahlin, for example, the mapped Franklin soil landscape has deep, imperfectly drained sodic soils and widespread seasonal waterlogging, which a slab design has to allow for. See our page on structural engineering in Gungahlin.

Backyard sewer mains

If a sewer main runs through your backyard, plan around it from the start. Icon Water's guidance says its building approval is needed before work starts, and footings are not permitted inside the pipe's protection envelope. We don't quote clearance distances from memory: Icon Water's requirements for your pipe decide them. Footing design near a main starts at $790 + GST ($869 inc GST). Read building near a sewer in Canberra, or see our sewer and stormwater design service.

Slopes, frames and the existing house

On a sloping block the granny flat may need a retaining wall. A wall up to 1.2 m high, measured to the lowest ground next to it, needs no building approval; above that the rules tighten. Within 1.5 m of a side or rear boundary, a wall over 0.4 m loses its planning exemption. The frame needs bracing, tie-downs and fixings designed for the structure, steel or timber. If a dual occupancy attaches to or alters the existing house, we check that structure too.

When should you call a structural engineer?

Call once you have a concept plan, before the design is fixed. Footings, a sewer main or a slope can move the building on the block, and that is cheaper to deal with on paper.

• For a granny flat or dual occupancy: our granny flat and dual occupancy engineering is a fixed quote from your plans.
• For the slab only: footings, slabs and site classification from $1,290 + GST ($1,419 inc GST).
• For three or more homes: see townhouse and multi-unit engineering.
• Starting from a cleared block: see knock-down rebuild engineering.

Send your plans or a sketch, a few photos of the block and where any maintenance hole sits. Add up to 5 files. We reply with a fixed quote in under 20 minutes on average, during business hours. We're engineers only: we don't build granny flats or recommend builders, so our design isn't tied to anyone's contract.

Prices are the same across Canberra, Queanbeyan, Jerrabomberra and Googong. Across the border, NSW rules apply instead of the ACT rules on this page; we work with QPRC and your certifier there.