Planning · Secondary Dwellings
Apr 2025
For decades the Queensland granny flat was a quietly absurd piece of regulation: you could build one, but a state-level rule restricted who could live in it. Adult children, ageing parents, family carers — fine. Anyone else? Technically not. Most councils didn't enforce it; most owners didn't know the rule existed; the rental market quietly ignored it. Then, on 26 September 2022, the state changed the rule.
The 2022 reform — what changed
The Planning (Secondary Dwellings) Amendment Regulation 2022 removed the "household member" restriction state-wide. Since then, a secondary dwelling on a Brisbane lot can be rented to anyone — a stranger, a tenant, a short-stay guest (subject to your council's separate short-stay rules). The state's changes to secondary dwellings page confirms the policy intent: to lift effective housing supply by activating the existing stock of granny flats sitting empty because owners couldn't legally rent them.
The reform also clarified the design pathway. Compliant secondary dwellings on most Brisbane residential lots are now accepted development at the planning layer — meaning no DA, just a Building Approval — provided you stay inside the rules.
The rules that still apply
The pathway to "accepted development" requires meeting the State Code for a Dwelling House that is a Secondary Dwelling. The headline constraints:
Size — 80 m² maximum gross floor area. This is the biggest single constraint. 80 m² is enough for a two-bed, one-bath unit or a generous one-bed; not enough for a family of four. Decks and porches are excluded from the GFA count if they're unenclosed.
One secondary dwelling per lot. You don't get to build two.
The principal dwelling has to exist. A granny flat is "secondary" — it can't be the first thing built on a vacant lot.
Compliance with the lot's zone provisions — setbacks, site cover, building height, the usual Brisbane City Plan controls.
Where one or more of those rules can't be met (typically size — clients increasingly want 100–110 m² to make the unit liveable for a family member long-term), the project drops out of accepted development and into code-assessable at the planning layer. A code-assessable DA is achievable; it just costs $4,000–$10,000 in fees and adds 8–14 weeks. We tell clients early which side of the 80 m² line their brief sits on so they can decide.
Where it goes wrong
The most common mistake we see: counting on a granny flat's rental income to justify the build, then discovering that the only feasible site placement triggers a flood overlay, a character overlay, or a vegetation protection overlay — each of which can take the project from accepted development to impact-assessable, blowing out the timeline and budget. Cheap, fast secondary dwellings exist; they exist on sites where the overlays cooperate. Run the overlay check before you spend money on a concept.
Second mistake: assuming "one parking space" is enough. The state code requires at least one space for the secondary dwelling on top of the principal dwelling's requirement. Brisbane lots tight on driveway frontage often can't add a second hardstand without losing trees, which itself can trigger another assessment layer.
The economics in 2026
An 80 m² secondary dwelling in Brisbane, built to current code with reasonable finishes, runs $250,000–$380,000 depending on access, drainage, and connection costs. At current Brisbane rents for two-bed units in established suburbs (the Queensland Government Statistician tracks this quarterly), gross yield sits at 5.5–7.5% on the cost-to-build — competitive with most investment property classes, with the added optionality of being able to move a family member in later. Add the depreciation tail and the build typically pays itself off in 10–14 years.
Where this is heading
State and federal governments have explicitly framed secondary dwellings as a housing-supply lever. Expect further easing of the rules over the next five years — likely candidates: lifting the 80 m² cap to 100 m², simplifying parking requirements, and a state-level "permitted use" framework that takes the council layer out of the equation entirely for compliant builds. The 2022 reform was a first step; the political pressure is for more.
For homeowners considering one: build it well, not cheap. Insulate it like the main house. Run it electric (heat pump hot water, induction cooktop, split-system, solar shared from the main roof). A secondary dwelling that hits 7-star NatHERS and Whole-of-Home 60 — same standard as the main house — will let your tenant or family member live there for decades without an unaffordable power bill.
If you'd like us to check whether your block can carry a secondary dwelling under accepted development, get in touch.
By Ashton Genrich — Building Design — Open, QBCC 15387939