Short answer
Extensions typically cost about $2,500 to $4,500 per m² for a single-storey addition (a 40 m² extension is $100,000 to $180,000), $3,500 to $5,500 per m² for a second storey, $2,000 to $3,500 for a granny flat, $1,000 to $1,800 for a garage conversion and $300 to $700 for a deck or pergola, at standard finish. Council fees, engineering and site work are extra.
Our free home extension cost calculator gives an instant, indicative estimate for ground-floor extensions, second-storey additions, granny flats, decks and garage conversions anywhere in Australia. Pick your extension type, enter the floor area you want to add, and choose your finish level to see a realistic price range in seconds.
Estimate the cost to add living space to your home. Indicative AUD ranges.
Included: typical materials, labour, and standard fittings for the selected extension type. Not included: council application fees, engineering certification, asbestos handling, site excavation (sloped blocks), or feature finishes beyond the selected level. City and size adjustments are approximate rules of thumb.
Indicative Australian estimate only — final quotes vary with city, access, property condition, materials, structural/plumbing/electrical changes, waterproofing and permits. Ranges last reviewed 24 September 2026.
How to use this home extension cost calculator
Pick the type of extension you're planning, enter the floor area you want to add, and select the finish level you're targeting. The calculator returns an indicative AUD price range that reflects current Australian builder rates for materials and labour combined.
These are indicative ranges — final pricing depends heavily on site access, structural complexity, your local council, and the builder's current workload. Use this to budget; get at least two written quotes before committing.
How much does a home extension cost in Australia?
Across Australia in 2026, a typical ground-floor home extension costs $2,500–$4,500 per square metre for a standard finish. A 40 m² extension therefore lands around $100,000–$180,000. Adding a second storey runs higher, at $3,500–$5,500/m², because you're adding structural reinforcement to the existing house and working at height.
Detached granny flats are the most cost-efficient way to add bedrooms, typically $2,000–$3,500/m² ($120,000–$210,000 for a 60 m² unit). At the low end of the scale, decks and pergolas come in at roughly $300–$700/m², while converting an existing garage to habitable space sits between at $1,000–$1,800/m².
Home extension cost by type
| Extension type | Per m² (standard finish) | Typical scope (40–60 m²) | Typical total |
|---|---|---|---|
| Single-storey ground floor | $2,500–$4,500 | Living + bedroom or master suite | $100,000–$270,000 |
| Second-storey (upper) addition | $3,500–$5,500 | 2–3 bedrooms + bathroom | $210,000–$330,000 |
| Granny flat (detached) | $2,000–$3,500 | Studio or 1–2 bedroom self-contained | $80,000–$210,000 |
| Deck or pergola | $300–$700 | Outdoor entertaining area (30–60 m²) | $9,000–$42,000 |
| Garage conversion | $1,000–$1,800 | Existing structure to living space (30–45 m²) | $30,000–$80,000 |
What affects your home extension cost?
Structural complexity
Single-storey extensions on slab are simplest. Adding a second storey requires engineering certification, structural reinforcement of the existing house, scaffolding, and temporary weather protection — all of which add 30–50% over a comparable ground-floor build.
Site access
If your builder can't get a small excavator to the work area, costs rise. Inner-city blocks with narrow access, sloped sites, or builds that require crane lifts (common for second-storey work) can add 15–25%.
Services and council
Extensions almost always require relocating or extending plumbing, electrical and sometimes gas. Council planning approvals can take 2–6 months in metro councils and add several thousand dollars in fees plus consultant costs (engineer, energy rater, town planner) for anything beyond a simple Complying Development.
Finish level
Standard finishes (laminate joinery, basic tiles, vinyl plank, off-the-shelf fixtures) sit at the lower end of each range. Premium finishes (stone benchtops, designer tiles, engineered timber, premium fixtures, architectural detailing) easily double the cost.
Materials and labour pressure
2024–2026 has seen the cost of structural timber, steel, and skilled trades stay elevated post-pandemic. Quotes from one quarter often don't hold for the next; expect a 5–10% buffer for material variations.
Why some people extend instead of buying an investment property
Many Australian homeowners compare the cost of extending with the cost of buying a second property. Some points to weigh (tax rules change, so confirm the current position with an accountant):
- Main residence exemption. Capital gains on your main residence are generally CGT-free, so money spent extending it does not normally create a CGT liability when you sell (special rules can apply if part of it is rented out or used for business).
- Investment property gains are taxable. A capital gain on an investment property is generally taxed at your marginal rate, with a discount for assets held over 12 months for individuals. Tax settings for investors have been debated in recent years, so check the current rules.
- Stamp duty avoided. Buying an investment property triggers state transfer (stamp) duty, which can run to several percent of the purchase price depending on the state and price. Extending doesn't.
- Family-stage flexibility. A second storey or granny flat solves the "growing family or aging parents" problem in the home you already own, without the costs of selling and re-buying.
The trade-off: an extension is harder to liquidate than property and concentrates risk in one asset. Get advice from your accountant and a buyer's agent before committing — the math depends on your marginal tax rate, your current home's value, and how long you plan to stay.
Home extension cost by city
| City | Single-storey (per m², standard finish) | Notes |
|---|---|---|
| Sydney | $2,750–$4,950 | Highest in AU; site access in older suburbs adds cost |
| Melbourne | $2,600–$4,700 | Heritage overlays common in inner suburbs; permits longer |
| Brisbane | $2,500–$4,500 | Queenslander style raises; under-house conversions popular |
| Perth | $2,500–$4,500 | Approval times vary by council |
| Adelaide | $2,400–$4,300 | Generally a little below the national average; granny flats are popular |
| Hobart | $2,400–$4,300 | Smaller builder pool; lead times can be long |
| Regional QLD/NSW/VIC | Varies | Materials cost about the same; trade availability and travel can add cost |
City figures are the national range adjusted by the same approximate city multipliers the calculator uses (Sydney +10%, Melbourne +5%, Adelaide and Hobart -5%). Real prices vary by suburb and site.
Frequently asked questions
Do I need council approval to extend my home?
Most likely yes. Small decks under certain heights and detached structures under ~10 m² may qualify as exempt or Complying Development in some states, but anything that adds habitable floor area, changes the building envelope, or involves structural work needs Development Approval (DA). Check with your local council early — approval timelines often dominate the build schedule.
How long does a home extension take?
Plan for 4–8 months total: 2–4 months of design, council approval, and selecting a builder, then 3–6 months of construction. Second-storey additions and complex sites can stretch this to 12+ months.
Can I live in the house during a home extension?
Often yes for ground-floor extensions where the existing house stays sealed off, but the noise, dust, and temporary loss of an external wall can be disruptive for 6–12 weeks. For second-storey additions, the roof comes off — most families move out for the structural phase.
What's the cheapest way to add a bedroom to my house?
Converting an existing space (garage, large laundry, formal lounge) is cheapest at roughly $1,000–$1,800/m². A detached granny flat is the cheapest "new build" option at $2,000–$3,500/m². Both are dramatically less than buying a larger home or building a new investment property.
Does a home extension add value equal to its cost?
Not always. Returns vary widely. Well-executed extensions in high-demand suburbs can add as much value as they cost, while over-capitalising (a luxury extension in a modest suburb) typically returns less than you spend. A local buyer's agent or valuer can sanity-check before you commit.
Should I extend or build a granny flat?
If you need more living space for the family, extend. If you need a separate dwelling for rental income, an aging parent, or an adult child, build a granny flat. Granny flats can also be rented out (rules vary by council/state) and offer the cleanest exit if you sell the main house later.
How we calculate these estimates
Our ranges are indicative rules of thumb compiled from published Australian builder and cost-guide figures, which we cross-check against each other and which lean towards builder marketing rates. They are not drawn from a proprietary cost database. The calculator's city and finish multipliers (for example 1.25x for an upgraded finish) are our own simple approximations, so treat the output as a starting budget and get written quotes.
We review these ranges periodically. Last reviewed: 24 September 2026.
Related reading: Granny Flat Cost Australia (2026) (granny flat costs and what drives the price); Second Storey Extension Cost Australia (2026) (what adding a second storey costs).
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