What counts as a granny flat
A granny flat is a small, separate home or studio in the grounds of an existing house, used by family members, tenants or as a home office. A cost guide notes that South Australia sets limits on what counts as a granny flat, and that approval, site preparation and services are often quoted apart from the build. A second builder's guide adds that the planning term is a secondary dwelling if detached, and ancillary accommodation if attached to the house. Ask your council which applies to your block.
What the published prices say
A cost guide updated in October 2026 gives $110,000 to $160,000 turnkey for a one-bedroom granny flat of 35 to 45 square metres, and $140,000 to $210,000 for a two-bedroom of around 60 square metres, including GST. A second guide gives $90,000 to $150,000 and $130,000 to $190,000 for similar sizes. They differ, and they are indicative published ranges, not quotes. Ask each builder what a turnkey price includes.
Site works and services
The cost guides say site works and service connections can be a large separate item. One guide gives $15,000 to $40,000 for site works and connections, and notes that connecting water and power, wastewater where there is no sewer and retaining walls on sloping blocks can each add thousands. Ask each builder what is connected, where the meter and the pipes will run, and whether the quote includes the trenching.
Approvals
The first cost guide gives $3,000 to $11,000 for development approval and building consent on a granny flat. A builder's guide says extensions need approval under the Planning and Design Code, and PlanSA points to code.plan.sa.gov.au for the policies at an address. Ask your council what applies, and ask who lodges the application.
Prefab and modular
The cost guide says prefabricated or modular one-bedroom units are listed from about $80,000 to $120,000 delivered, before they are connected and finished on site. That is not the same as a finished dwelling, so ask exactly what is included in any prefab quote, including the slab, the crane, the connections and the fit-out.
Licence and insurance
Ask for the building work contractor licence details and check it on the SA licence register. The SA Government says building indemnity insurance is required for domestic work needing council approval and costing $20,000 or more, and the certificate should reach you and the council before work starts.
Using a granny flat
Think about who will live in it, how they will get in and out, and how it affects the yard. Ask about privacy, parking, and fencing, and ask about how services will be metered if you intend to rent it. Check the rules with your council before you plan to rent it out.
Planning the layout
A granny flat is a small home, so the layout matters. Think about a kitchen, a bathroom, a laundry, storage and a place to sit outside. If it is for an older relative, think about step-free access, wider doorways and a bathroom they can use safely. If it is a studio, think about power, internet, lighting and heating and cooling.
Privacy and access
Ask how people will reach the new building without walking through the main house, how the paths and lighting will work at night, and how the fencing will be handled. Ask each builder what is in the price for a path, a driveway extension or parking, and ask about bins, post boxes and the address, because those are often forgotten.
Prefabricated or built on site
Some granny flats arrive as factory-built modules and some are built on site. The first can be faster on site, but the slab, crane, delivery, connections and finishes still have to be paid for. The second can be adjusted to fit the yard. Ask each business how long the build would take once approvals are done, and what the contract says about delays.
Heating, cooling and energy
A small building can be comfortable or miserable depending on its insulation, windows and orientation. Ask each builder how the flat will be heated and cooled, what insulation is included and how the hot water is supplied, and ask what the running costs might look like for the people living in it.
How much does a granny flat cost in Adelaide?
A cost guide updated in October 2026 gives $110,000 to $160,000 turnkey for a one-bedroom of 35 to 45 square metres and $140,000 to $210,000 for a two-bedroom of about 60 square metres. Another guide gives lower figures. They are not quotes.
Do I need approval for a granny flat?
Usually. Cost guides say approval and site works are often quoted separately. Use code.plan.sa.gov.au and ask your council.
Can I rent out a granny flat?
That depends on the planning rules and your council. Ask the council before you build.
What is the difference between a studio and a granny flat?
There is no single answer. Ask your council how a studio would be treated for approval.
Sources
- What's The Damage: granny flat cost Adelaide (updated October 2026)
- RAW Structures: how much does a home extension cost in Adelaide (25 August 2026)
- PlanSA: find out if you need approval
- SA.GOV.AU: building work contractor's licence
- SA.GOV.AU: check occupational licence holders
- SA.GOV.AU: building indemnity insurance