Costs, Price Drivers and 2026 Rules
Granny flat cost in Australia: building a secondary dwelling on your block
Illustrative granny flat costs in Australia, what drives them, state approval pathways for secondary dwellings, services connections and the contract rules to check.
A granny flat (a secondary dwelling or small second dwelling) costs roughly what a small self-contained house costs: slab or footings, frame, roof, a kitchen, a bathroom and connections to water, sewer, power and stormwater. The biggest swing factors are site preparation and services connections, which can cost as much on a difficult block as the fit-out does on an easy one, plus the approval pathway your state offers. As an illustrative band, a detached granny flat with a standard finish might sit around $2,500 to $4,200 per m² including GST, so a 60 m² two-bedroom unit would be roughly $150,000 to $252,000 before approvals, connections and contingency.
This guide is part of the renovation cost overview. For an attached addition rather than a separate dwelling, read the home extension guide.
Kit, modular or custom-built?
| Delivery type | How it works | Good for | Watch out for |
|---|---|---|---|
| Kit home | You buy a frame and materials kit; a builder or owner-builder assembles it | Owners with building experience and time | Kit price excludes slab, services, trades and fit-out |
| Modular or prefabricated | Built in a factory, delivered and craned onto footings | Sites with crane access; tighter programme | Crane and transport costs; deposit rules for off-site work differ in some states |
| Custom builder | Designed and built on site by a licensed builder | Unusual blocks or designs that must match the house | Longer programme; more design fees |
In Queensland, for example, the deposit cap rises to 20% where more than half of the contract value is off-site work, which is common with modular builds. Check your state's rules before paying a factory deposit.
What drives the cost
- Size and layout. Each extra bedroom adds area, but the kitchen and bathroom cost much the same in a one-bedroom or two-bedroom unit.
- Site works. Slope, rock, fill, trees and access for concrete trucks.
- Services. Distance to the sewer junction and the switchboard, whether the electricity supply can take the extra load, and whether the water authority requires a separate meter or a new connection fee.
- Bushfire or flood controls. Bushfire attack level (BAL) ratings increase construction requirements.
- Finish level. Flooring, cabinetry, glazing and heating and cooling.
- Approval pathway. Fast-track routes reduce time and fees where your site qualifies.
Worked example (illustrative)
A 60 m² two-bedroom detached granny flat on a flat suburban block with rear lane access.
- Area x rate: 60 x $2,500 = $150,000 (low) and 60 x $4,200 = $252,000 (high).
- Fixed costs: design and drafting $5,000; soil test and engineering $3,000; approval and certifier $5,000; sewer, water and power connections priced as a provisional sum $15,000. Total $28,000.
- Range: $178,000 to $280,000.
- Contingency of 10% on the high end: $28,000.
- Planning budget: up to about $308,000, including GST.
The rate band and fixed costs are illustrative assumptions. Run your own numbers with the renovation cost estimator and the contingency calculator.
Approval pathways by state (overview)
States have been making small second dwellings easier to approve, but the details vary and change. Treat this table as a starting point and confirm with your council or a certifier.
| State | Pathway to check |
|---|---|
| NSW | Secondary dwellings can often use complying development under the State housing planning policy if the lot and design meet the standards (including size limits); otherwise a development application |
| Victoria | Planning reforms allow many small second dwellings without a planning permit where they meet set requirements; a building permit is still required |
| Queensland | Secondary dwellings are regulated through local planning schemes; recent State changes allowed more granny flats to be rented to people who are not family, so check the current position |
| Other states | Check the state planning portal and your council |
Granny flats can also raise questions beyond building approval: council rates, land tax, capital gains tax on a future sale of the main residence if part of the property is rented, and the tax treatment of rent. Those are tax questions, so check the Australian Taxation Office and consider a tax adviser.
Contract, licence and insurance
A granny flat is residential building work far above every state's thresholds. Expect a written contract, a licensed or registered builder, a deposit cap and home warranty or domestic building insurance. For a modular builder, check who the contracting party is: the factory, an installer or a local builder, and who holds the licence and insurance certificate. See renovation rules by state and how to check a builder's licence.
If you plan to build as an owner-builder, a permit is generally required above the state threshold, and home warranty rules on a later sale may apply. Read owner-builder permits first.
Mistakes to avoid
- Comparing a kit price with a builder's turnkey price.
- Leaving connections out of the budget. Sewer and electrical upgrades are the most common surprise.
- Assuming you can rent the flat out; check the planning rules and any conditions of approval.
- Not checking easements and the location of the sewer main before choosing a position.
FAQ
Is a granny flat cheaper per m² than an extension?
Sometimes, because it is simple and separate from the house. But a self-contained unit needs its own kitchen, bathroom and services, which offsets the saving.
Do I need a separate electricity meter?
Not always. It depends on your distributor's rules and whether you plan to rent it out. Ask your electrician.
Can I build a granny flat in a strata scheme?
Usually not without strata approval, and often not at all on common property.
How long does a granny flat take?
Modular builds can be quicker on site; custom builds take longer. Approval time often matters more than construction time.
Sources
- NSW Planning Portal — secondary dwellings and complying development
- Planning Victoria — small second dwellings
- Queensland Building and Construction Commission — deposits, including for off-site work
- Australian Taxation Office — tax treatment of renting part of your home
- Building Commission NSW, via NSW Government — contracts and insurance in NSW
