The maximum size of a granny flat depends on which state you are in and, just as importantly, which approval path you use. In most states a secondary dwelling of up to around 60 m² of internal living area can be approved quickly under a fast-track pathway — but the exact cap, and what counts toward it, varies. Here is the state-by-state picture, plus the setbacks and rules that decide whether you get a fast approval or a slow one.
Rules change and councils apply their own overlays — always confirm with your local council or a private certifier before you design. This is general information to help you plan.
Maximum granny flat size by state (indicative)
| State/Territory | Typical max internal size | Fast-track pathway |
|---|---|---|
| NSW | ~60 m² | State-wide complying-development pathway (min. 450 m² lot) |
| VIC | ~60 m² (small second dwelling) | State small second dwelling reforms |
| QLD | Varies by council; often ~60–80 m² | Secondary dwelling under local planning scheme |
| WA | ~70 m² (ancillary dwelling) | State planning policy for ancillary dwellings |
| SA | ~60 m² | Council/secondary dwelling rules |
| TAS / ACT / NT | Council-dependent | Confirm locally |
Internal living area usually excludes the garage, patio, veranda and eaves — so a 60 m² cap can still give you a comfortable one- or two-bedroom home. Confirm exactly what your state counts toward the cap.
What actually decides your maximum size
- Minimum lot size. Many fast-track pathways require a minimum block (e.g. ~450 m² in NSW). Smaller blocks may still allow a granny flat via a council development application, but with more conditions.
- Setbacks. Distance required from boundaries, the main house and easements. Tight setbacks can cap footprint before the size rule does.
- Site coverage. Total built area (house + granny flat + garage) as a share of the block.
- Height and overshadowing. Single-storey is simplest; two-storey triggers more scrutiny.
- Approval path. A complying-development / fast-track certificate is quicker but has strict size and setback limits; a full development application allows more flexibility but takes longer.
If council approval is your sticking point, our guide on granny flat council approval walks through both pathways.
Bigger is not always better — the finance angle
A larger granny flat costs more to build, so it needs more funding — but it can also earn more rental income and add more value. Lenders assess the build cost and, where relevant, the expected rental income when sizing your finance, so the smart move is to design to the size your budget and serviceability support, not just the maximum the rules allow. See how much a granny flat costs to match size to budget, and granny flat designs for layouts that use the allowed area well.
Comparing options? Granny flat vs extension covers when a separate dwelling beats adding a room.
Planning a granny flat and want to know what you can build — and fund? Talk to Little Home Loans on 1300 391 390, apply online, or get in touch.
Frequently asked questions
How big can a granny flat be in Australia?
In most states a secondary dwelling of up to around 60 m² internal living area can be approved under a fast-track pathway. WA allows up to about 70 m², and some states or councils permit more via a full development application. Confirm your state and council rules.
How big can a granny flat be in NSW?
Up to about 60 m² internal living area under the state-wide complying-development pathway, generally on a lot of at least 450 m². Larger may be possible via a council development application.
Does the garage or patio count toward the size limit?
Usually no — the cap typically applies to internal living area and excludes garages, patios, verandas and eaves. Check exactly what your state counts before designing.
Can I build a two-bedroom granny flat?
Yes. A 60 m² allowance is generally enough for a comfortable one- or two-bedroom layout, depending on the design and how efficiently the space is used.
Does granny flat size affect my finance?
Yes. A bigger build costs more and needs more funding, but can earn more rental income and add more value. Lenders consider build cost and, where relevant, expected rent when sizing your loan.
This article is general information only and does not constitute credit, financial, legal or planning advice. Granny flat size, setback and approval rules vary by state and council and change over time — confirm current requirements with your local council or a private certifier. Lending is subject to approval, lending criteria, terms, conditions and fees. Little Home Loans arranges finance under Australian Credit Licence 506065 (Five Tees Pty Ltd).
Written and reviewed by the Finance Director at Little Home Loans.
