A professionally built granny flat in Australia costs roughly $80,000 to $160,000 or more, with custom or two-storey designs running past $200,000. In Sydney, turnkey site-built units price at about $2,300 to $3,500 per square metre including GST: a one-bedroom unit of 35 to 45 m2 at $110,000 to $160,000, and a two-bedroom unit of around 60 m2 at $140,000 to $210,000. Modular units start lower, from about $80,000 delivered, but the delivered price usually excludes footings, services and approvals.
This guide gives the dated figures, the difference between modular and site-built, and the rules in each state that decide what you can build and whether you can rent it out. All figures are Australian dollars. No primary quantity surveying table publishes a granny-flat-specific rate, so every price below is from a secondary source and is labelled as such.
The short answer
| Item | Range | GST | Source and date |
|---|---|---|---|
| Professionally built granny flat, total | $80,000 to $160,000+, custom over $200,000 | Not stated | Canstar quoting hipages, 12 November 2025 |
| DIY one-bedroom kit, shell only | Under $30,000 | Not stated | Canstar, 12 November 2025 |
| Turnkey site-built, per m2, Sydney | $2,300 to $3,500 | Included | whatsthedamage.com.au, October 2026 |
| One bedroom, 35 to 45 m2, turnkey, Sydney | $110,000 to $160,000 | Included | whatsthedamage.com.au, October 2026 |
| Two bedroom, about 60 m2, turnkey, Sydney | $140,000 to $210,000 | Included | whatsthedamage.com.au, October 2026 |
| Prefab or modular unit, delivered | From about $80,000 | Included | whatsthedamage.com.au, October 2026 |
| Custom or two-storey design, Sydney | $260,000 to $425,000 | Included | whatsthedamage.com.au, October 2026 |
| Prefab or kit build, installed, national | $95,000 to $140,000 | Not stated | Three Birds Renovations, 14 May 2026 |
| Project or volume build, national | $140,000 to $210,000 | Not stated | Three Birds Renovations, 14 May 2026 |
| Semi-custom build, national | $210,000 to $280,000 | Not stated | Three Birds Renovations, 14 May 2026 |
| Fully custom architect-designed, national | $280,000 to $400,000+ | Not stated | Three Birds Renovations, 14 May 2026 |
Sources: Canstar, What does it cost to build a granny flat, 12 November 2025; whatsthedamage.com.au, Granny flat cost Sydney, October 2026, an aggregator that states its figures are checked against Australian trade data; Three Birds Renovations, How much does it cost to build a granny flat, 14 May 2026, which cites no sources for its estimates. Checked 7 October 2026.
For context, BMT's 2026 Construction Cost Table has no granny flat row. Its closest entry, a two-bedroom single-level brick veneer townhouse at $3,291 to $4,200 per m2 in Sydney excluding GST, includes a common-property allowance and overstates a backyard unit. Treat the per-m2 figures above as planning guides, not quantity surveyor rates.
Modular or built on site?
Modular and prefab units are built in a factory and delivered. Entry pricing is lower, from about $80,000 delivered in Sydney or $95,000 to $140,000 installed nationally, and the build is faster. The trade-offs are fixed designs with limited modification, and a delivered price that usually excludes footings, service connections, crane and transport, and approvals. Ask for the installed, connected, approved price before comparing it with a site-built quote.
Site-built units are fully customisable and sit naturally with the main house. In Sydney, one-bedroom turnkey units run $110,000 to $160,000 and two-bedroom units $140,000 to $210,000 including GST. Nationally, the professionally built bracket is $80,000 to $160,000 or more. The build takes longer and depends more on site access.
What changes the price
- Size and bedrooms. A one-bedroom 35 to 45 m2 unit against a two-bedroom 60 m2 unit. State caps of 60 m2 in New South Wales and Victoria and 70 m2 in Western Australia shape the typical footprint.
- Services. Sewer and stormwater runs across the block, a power upgrade or separate metering, and crane or truck access for a modular delivery.
- Approvals pathway. Complying development or exempt pathways are faster and cheaper than a full development application. Infrastructure contributions apply in some councils.
- Finish and inclusions. Whether "turnkey" includes a kitchen, laundry, air conditioning, floor coverings, window coverings and landscaping.
- Site. Slope, soil class, trees, retaining and the distance from the street.
State rules: what you can build and who can live in it
| State | Rule | Source |
|---|---|---|
| New South Wales | Secondary dwellings are permitted in R1 to R5 zones under the Housing SEPP 2021. Complying development needs a lot of at least 450 m2. The floor area must not exceed 60 m2 or 60 percent of the principal dwelling's floor area, whichever is greater. The lot cannot be subdivided. | NSW Planning, Secondary dwellings, updated 17 July 2025; council summaries from Shoalhaven and Hornsby |
| Victoria | From 14 December 2023, a small second home up to 60 m2 needs no planning permit on lots of 300 m2 or more in residential zones without flood or bushfire overlays. A building permit is still required. Anyone may live in or rent it. It cannot be subdivided or sold separately. | Premier of Victoria, New granny flat reforms come into effect, 16 December 2023 |
| Queensland | From 26 September 2022, secondary dwellings may be rented to people outside the main household. Development and building approvals still apply, and local planning schemes set size limits. | Queensland Residential Tenancies Authority, 31 October 2022; SL 2022/133 |
| Western Australia | Ancillary dwellings up to 70 m2 that meet setback requirements are exempt from development approval on residential lots of any size, and generally need no extra parking bay. In effect from 16 April 2024 with the revised R-Codes. | WA Government media statement, 30 January 2024; WA Planning, Revised R-Codes, 16 April 2024 |
Rules change and councils apply them differently. Confirm the current position with your council or a certifier before you sign a build contract.
How to get comparable quotes
- Decide site-built or modular first, then compare like with like.
- Ask for the complete installed price: footings, services, connections, approvals, crane and transport, and GST.
- Ask what "turnkey" includes and get the inclusions in writing.
- Check your approvals pathway with the council before you brief builders; it changes the timeline and the fees.
- If you are weighing a granny flat against extending the main house, our home extension cost guide has the ranges.
The estimator below this article gives a modelled starting range from your answers, in Australian dollars. It does not inspect your block or replace a priced scope.
Frequently Asked Questions
How much does a granny flat cost in 2026?
About $80,000 to $160,000 or more professionally built nationally, according to Canstar quoting hipages in November 2025. In Sydney, turnkey site-built units run $110,000 to $160,000 for one bedroom and $140,000 to $210,000 for two bedrooms including GST, according to whatsthedamage.com.au in October 2026.
What is the cost per square metre for a granny flat?
About $2,300 to $3,500 per m2 turnkey in Sydney including GST (whatsthedamage.com.au, October 2026). No primary quantity surveyor table publishes a granny-flat rate, so treat this as a planning figure.
Is a modular granny flat cheaper?
Entry pricing is lower, from about $80,000 delivered or $95,000 to $140,000 installed, but delivered prices usually exclude footings, service connections, crane and transport, and approvals. Compare the complete installed and approved price with a site-built quote.
Do I need a planning permit for a granny flat?
It depends on the state. New South Wales offers complying development on lots of 450 m2 or more with a 60 m2 cap. Victoria needs no planning permit for units up to 60 m2 on lots of 300 m2 or more without overlays, but a building permit is required. Western Australia exempts ancillary dwellings up to 70 m2 from development approval. Queensland still requires approvals, with size set by the local scheme.
Can I rent a granny flat to anyone?
Victoria has allowed it since December 2023 and Queensland since 26 September 2022. In New South Wales, secondary dwellings under the Housing SEPP may be rented, but the lot cannot be subdivided. In Western Australia, ancillary dwellings may be rented under the R-Codes exemption. Check your council's current position.