Granny Flat Cost Calculator
Estimate what a granny flat or secondary dwelling costs to build in Australia. Set the floor area and bedrooms, choose the build type, then account for your site.
Ask any builder whether their price is fixed or subject to a soil classification. An M or H class reactive clay site can add $8,000 to $20,000 in footing upgrades that a P class quote simply did not include.
Rental yield on a well placed granny flat commonly lands between 10 and 15 per cent of build cost per year in capital city fringe suburbs, but check the local rental market for two bedroom units before you assume it.
- Structure, frame and roof$77,550
- Internal fitout and finishes$54,750
- Slab, footings and site works$41,050
- Services and connections$29,650
- Design, approvals and certification$25,100
💰 Ways to save
- Build within the state exempt development pathway rather than lodging a full DA. In NSW the SEPP allows a complying development certificate for a compliant 60m² secondary dwelling, which is assessed by a private certifier in roughly 10 to 20 days rather than the two to four months a DA takes. That time saving is real money in holding costs, and it also removes the neighbour notification risk that can derail a project entirely.
- Position the build to reuse the existing services. Every metre you move away from the main house adds trenching for water, sewer, power and data, at roughly $80 to $150 per metre. Siting the granny flat within 10 to 15 metres of the existing connection points, and ideally on the same side as the sewer junction, routinely saves $5,000 to $12,000 against a rear corner placement.
- Standardise the design. Builders who repeat a small number of floor plans buy trusses, windows and cabinetry in volume and can price 10 to 20 per cent below a custom set of drawings. If you want a custom look, spend the money on cladding and the kitchen, which are visible, rather than on a bespoke footprint, which is not.
- Get the soil test and a survey done before you sign anything. Both together cost around $1,200 to $2,500, and they convert the two largest variables (footing design and site levels) from unknowns into fixed line items. Builders price risk into vague quotes, so removing the unknown usually saves more than the test costs.
or from $1,090/week over 5 years , indicative finance
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## What a granny flat costs to build in 2026
Pricing reviewed: June 2026.
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Pricing reviewed June 2026. Indicative Australian costs, not a quote.
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Understanding granny flat costs in Australia
What a granny flat costs to build in 2026
A completed granny flat in Australia in 2026 generally runs between $130,000 and $300,000, which on a per square metre basis is roughly $2,400 to $4,200 for a standard build and $4,500 or more for high specification work. A 60m² two bedroom secondary dwelling, built by a volume granny flat specialist on a flat block with easy access, typically lands around $160,000 to $210,000 turnkey. Smaller studios of 35 to 40m² start closer to $110,000 to $140,000. Kit and modular options quote lower on the headline number, often $90,000 to $150,000, but those figures frequently exclude the slab, the crane, the connections and the approvals, which is where the remaining money goes.
Why size does not scale the way you expect
Granny flats are unusually expensive per square metre compared with a full house, and the reason is that the costly rooms are all mandatory. A kitchen, a bathroom, a laundry point, a hot water unit and a switchboard are required whether the dwelling is 35m² or 60m², so a studio carries the same expensive infrastructure over half the floor area. That is why going from one bedroom to two often adds only 10 per cent to the total while adding 30 per cent to the usable space. If the numbers are close, the larger build is almost always the better value per square metre and the better rental proposition.
State rules and the approval pathway
Approval rules for secondary dwellings are set at state level and vary meaningfully. In New South Wales the Affordable Rental Housing SEPP allows a secondary dwelling of up to 60m² internal floor area on a lot of at least 450m² with a minimum 12 metre frontage, and a compliant proposal can go through a private certifier as complying development in around 10 to 20 days. Victoria has moved to allow small second dwellings up to 60m² without a planning permit in many residential zones, subject to conditions. Queensland treats them as secondary dwellings under the local planning scheme, with several councils now permitting separate tenancy. Western Australia allows ancillary dwellings up to 70m² and permits renting to any tenant. South Australia and Tasmania have their own thresholds again. The practical point is that you must confirm your specific council's controls before you commit to a size, because designing a 70m² flat in a 60m² jurisdiction means either a redesign or a full development application with a very different timeline.
Site conditions are the biggest variable
Two identical designs on two different blocks can differ by $50,000, and it is almost always site conditions rather than the building itself. Slope is the first factor. Anything beyond a gentle fall means cut and fill, retaining, and often a stepped or suspended slab. Soil classification is the second. A P (problem) or H2 (highly reactive clay) classification can push footing costs up by $10,000 to $25,000 against a stable A or S class site. Access is the third. If a concrete truck cannot reach the pour and a crane cannot reach the frame, everything is handled twice. Existing trees are a fourth, because a protected tree with a structural root zone overlapping your slab can force a redesign or a piered footing system.
Services, meters and connection costs
Connecting the new dwelling is a line item people consistently underestimate. Trenching water, sewer, power and data from the existing house runs $80 to $150 per metre depending on ground conditions and whether the path crosses a driveway. A separate electricity meter, which most landlords want so the tenant pays their own power, costs around $2,500 to $4,500 including the switchboard work and the retailer connection. If the sewer main crosses your building footprint you will need a build over sewer approval from the water authority, which costs a few hundred dollars to assess and can add engineered pier and beam footings on top. Stormwater is the quiet one, because adding 60m² of roof and hardstand changes the site discharge and some councils will require an on site detention tank at $4,000 to $9,000.
Regional variation and what it returns
Sydney is the most expensive market to build in, running perhaps 15 to 25 per cent above Brisbane or Adelaide for the same specification, driven by trade rates and the cost of compliance. Regional builds can be cheaper on labour but carry freight on materials and a thinner pool of certifiers. On the return side, a granny flat in a capital city fringe suburb commonly rents for $380 to $650 a week, which against a $190,000 build is a gross yield in the 10 to 17 per cent range, plus a valuation uplift on the property that is usually less than the build cost but not negligible. Before you rely on that, confirm your council actually permits the secondary dwelling to be rented to a third party, because a handful still restrict occupancy to a family member.
Take the estimate above as a planning bracket, then get three fixed price quotes on the same set of drawings, each with the soil classification stated, the site works itemised, and the connections and approvals either included or explicitly excluded. The excluded items are where granny flat budgets blow out.
Frequently asked questions
How much does a granny flat cost in Australia in 2026?
Typically $130,000 to $300,000 completed, or about $2,400 to $4,200 per square metre for a standard build. A 60m² two bedroom on a flat block with good access usually lands around $160,000 to $210,000 turnkey, while a 35 to 40m² studio starts closer to $110,000 to $140,000.
How big can a granny flat be?
It depends on the state. New South Wales allows up to 60m² internal floor area under the Affordable Rental Housing SEPP, on a lot of at least 450m² with a 12 metre frontage. Western Australia permits ancillary dwellings up to 70m². Victoria and Queensland generally work to a 60m² style threshold with local variation. Always confirm the exact figure with your council before designing.
Do I need a development application?
Not always. A compliant NSW secondary dwelling can be approved as complying development through a private certifier in roughly 10 to 20 days, which is far faster than a DA at two to four months. If your design exceeds the size limit, sits on an undersized lot, or is in a heritage or bushfire overlay, you will need a full application.
Why are granny flats so expensive per square metre?
Because the costly components are fixed regardless of size. A kitchen, bathroom, laundry, hot water unit and switchboard are required whether the dwelling is 35m² or 60m², so a small build spreads the same expensive infrastructure over less area. This is also why going from one bedroom to two often adds only about 10 per cent to the total cost.
What site conditions push the price up the most?
Slope, soil and access. A steep block needing cut, fill and retaining can add $20,000 or more. A P class or highly reactive H2 clay classification adds $10,000 to $25,000 in footing upgrades. No machine access means craning frames in at $2,000 to $4,000 a day and barrowing spoil out. Get a soil test and survey before signing a contract so these become priced items rather than variations.
Can I rent out a granny flat?
In most of the country, yes. New South Wales, Western Australia and increasingly Victoria and Queensland permit secondary dwellings to be rented to any tenant, though a small number of councils still restrict occupancy to family members. Typical capital city fringe rents run $380 to $650 a week, giving a gross yield of roughly 10 to 17 per cent against a $190,000 build. Confirm your local rules before relying on the income.
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