Cost guide
How much does a granny flat cost?
By Struqt’s architects · Updated June 2026
A granny flat in Australia typically costs from about $80,000 for a small studio up to $300,000+ for a two-bedroom, custom-designed build. A prefabricated granny flat is the cheaper entry point; a custom design on a tricky block sits at the top of the range. Site preparation, approvals, construction and utility connections each move the figure.
A studio (often prefabricated) sits at the low end; a two-bedroom custom build at the top.
What is a granny flat?
A granny flat — also called ancillary accommodation, a secondary dwelling, a small second dwelling or a dependent persons unit — is a self-contained dwelling on the same block as an existing main dwelling.
Granny flats often range from about 40m² up to 80m²+, usually with one or two bedrooms, a living space, a bathroom and a kitchenette. Most states set a maximum size for the streamlined approval pathway, and many require a minimum existing site area before you can add a secondary dwelling.
How big can a granny flat be?
| State / territory | Typical maximum size |
|---|---|
| Victoria, Tasmania, New South Wales | 60 m² |
| South Australia, Western Australia | 70 m² |
| Queensland | 80 m² |
| Northern Territory | 50–80 m²Varies by scenario. |
Maximum floor area generally allowed under each state’s streamlined approval pathway. Most states also require a minimum existing site area before you can add a secondary dwelling.
Where the money goes
Depends on access, soil type and land topography.
New water, electrical and other services extended from the existing home.
What moves the price on your block
Sloping or difficult land
$20,000–$100,000+Retaining walls, earthworks (cut & fill) and split-level designs all add cost on a sloping block.
Soil type
$10,000–$80,000+Your soil classification drives footing cost. Reactive clay needs more extensive footings and reinforcement; rocky ground costs more to excavate.
Planning overlays
$15,000–$60,000+Heritage, flooding and bushfire overlays under the planning scheme can add significant cost to a build.
What is overlay? →Service connections
$10,000–$30,000Sites without access to sewer, water or other services can need on-site solutions such as septic tanks or large rainwater tanks.
Internal fitout
Tens of thousandsFlooring, joinery, tiling heights, air conditioning and plumbing fixtures vary greatly in cost. Higher specifications can add tens of thousands of dollars.
External works
Often excluded from contractFootpaths, driveways, fencing and landscaping are commonly left out of contract pricing but are important to budget for.
Frequently asked questions
How big can a granny flat be?
It depends on your state. Victoria, Tasmania and NSW generally allow up to 60m² for the streamlined pathway; South Australia and WA up to 70m²; Queensland up to 80m²; and the Northern Territory 50–80m² depending on the scenario. Most states also require a minimum existing site area.
Is a prefab granny flat cheaper than a custom build?
Usually, yes. A prefabricated granny flat is a cheaper entry point — often near the bottom of the $80,000+ range — while a custom-designed, two-bedroom build sits at the top, $300,000 or more, especially on a block with access, slope or soil challenges.
Do I need council approval for a granny flat?
Almost always. A secondary dwelling normally needs approval, and most states run a streamlined pathway if you stay within the size and site-area rules. Statutory approvals typically cost $4,000–$18,000. Run your address through Struqt to see the pathway and rules for your block.
Disclaimer. The figures in this guide are estimates intended as a planning guide only. Actual costs vary significantly depending on your site, design, specification and current market conditions. Always seek detailed quotes from licensed builders, and factor in a contingency of 10–20% before committing to a budget.
Get the exact granny flat cost for your block
These are typical ranges. Run your address through Struqt to see the size limits, approval pathway and rules that apply to your specific block.