Ask three builders what the house extension cost per square metre in Australia is right now and you’ll probably get three different answers. That’s not necessarily a sign anyone is dodging the question. The per-square-metre rate moves around a lot depending on what you’re adding, where your block sits, and how far you want to push the finishes.
For 2026, Australian industry guides put most extensions somewhere between $2,800 and $5,500 per square metre. A straightforward ground-floor addition sits at the lower end of that band. Add a second storey and you climb toward the top, because structural engineering, scaffolding and roof removal all add real money. This guide lays out what homeowners are actually paying per square metre in 2026 — by extension type, by city, and line by line — so you can walk into builder conversations with a realistic budget already in your head.
Average House Extension Cost Per Square Metre in Australia (2026)
The table below pulls together 2026 figures from Australian builder and industry cost guides. Treat these as planning ranges, not quotes — your final number comes down to your block, your design and your finish level.
| Extension type | 2026 cost per m² | Typical total project cost |
| Ground-floor extension | $2,800 – $4,500 | $85,000 – $360,000 |
| Second-storey addition | $3,200 – $5,500 | $160,000 – $440,000 |
| Granny flat (turnkey) | $2,200 – $4,200 | $130,000 – $250,000 |
| Garage conversion | $1,800 – $3,200 | $45,000 – $95,000 |
| Wraparound extension | $3,000 – $4,800 | $180,000 – $480,000 |
Two things are worth knowing before you use these numbers. First, extensions usually cost more per square metre than a brand-new build, which sits around $2,400–$3,800/m² in most capital cities. That’s because you’re working around an existing house — tying in roof lines, matching brickwork, protecting the parts you’re keeping and staging work so the family can still live there.
Second, per-square-metre rates are a starting point, not the whole story. Fixed costs like council approvals, kitchen joinery and bathroom plumbing don’t shrink when the extension gets smaller, so compact additions often land at the higher end of the per-metre range.
What Your Extension Money Actually Goes On
A rear kitchen-and-dining extension of about 30m² is one of the most common projects in Australia. Here’s how the money can stack up on a mid-range job:
| Line item | Indicative cost |
| Build: 30m² × ~$3,400/m² | $102,000 |
| Kitchen joinery and appliances | $35,000 |
| Demolition of existing rear wall | $4,500 |
| Council DA, plans and engineering | $9,000 |
| Site costs, services and drainage | $12,000 |
| **Total** | **$162,500** |
Now for the costs people forget to budget. Full or partial demolition can run $25,000–$45,000 once disposal is included. Architectural or designer fees typically add $5,000–$15,000 for documentation. If you’re going up, you may need temporary accommodation while the roof is off. And almost every extension needs a contingency of 10–15 per cent, because opening up an old house has a way of revealing surprises.
If you’re weighing an extension against a broader renovation, our renovation costs guide for 2026 compares what kitchens, bathrooms and full-house projects are costing side by side.
Factors Affecting the Cost of a House Extension
Single storey vs second storey
Going up costs noticeably more per square metre. The existing footings were never designed to carry another level, so you can expect pier reinforcement, structural steel transfer beams, temporary roof removal and crane hire. Then there’s scaffolding for four to six months. A second storey typically runs $3,200–$5,500/m² against $2,800–$4,500/m² for ground floor.
Site access and soil
A flat block with clear side access is the cheapest scenario. A sloping block, reactive clay soil, a battleaxe block or a tight inner-city terrace all push the number up — through retaining walls, piering, pump-out systems or simply the extra labour of carrying everything in by hand.
Wet areas drive the price
A 30m² extension that’s mostly living space costs far less per metre than the same footprint split between a new bathroom, ensuite and laundry. Plumbing rough-in, waterproofing, tiling and drainage multiply the cost of every square metre they touch. If your extension includes a bathroom, budget at the top of your range.
Approvals: DA vs complying development
A full development application through council takes longer and costs more in consultant fees than a complying development certificate (CDC), where the design meets pre-set standards. Not every extension qualifies for the faster path, so confirm with your local council early — approval type affects both your timeline and your budget.
Finishes and joinery
Standard finishes versus premium ones can swing the per-square-metre rate by 25–40 per cent. Custom joinery, stone benchtops, floor-to-ceiling glazing and imported tapware are the classic budget stretchers. Decide your finish level before you get quotes, because comparing a standard-spec quote with a premium one tells you nothing.
Builder demand and labour
Extension work competes for the same tradies as new builds and renovations. In hot markets, good builders book out months ahead and charge accordingly. Labour shortages have been a running theme in Australian construction since 2020, and they’re still part of why quotes come in higher than many homeowners expect.
House Extension Costs by City
Where you build matters. Industry guides consistently put Sydney at the top of the price range, followed by Melbourne, with Brisbane and other capitals generally sitting lower.
Sydney
Expect to pay at the top end of every range — ground-floor extensions commonly land between $3,500 and $5,000+ per square metre. Tight inner-city access, heritage overlays and high land values all play a part. It’s no coincidence that the Housing Industry Association expects NSW renovation investment to outpace Victoria by nearly 50 per cent in 2026, with Sydney’s land prices pushing homeowners to extend rather than move (HIA housing outlook).
Melbourne
Melbourne sits a step below Sydney, with typical ground-floor rates around $2,800–$4,200/m². Competition among builders is strong, which helps. Watch for reactive soils in the growth corridors — footing upgrades on clay can add thousands before a single wall goes up. Inner-north and inner-east heritage controls can also complicate what looks like a simple rear addition.
Brisbane
Brisbane is generally the most affordable of the three capitals, with ground-floor extensions often quoted around $2,500–$3,800/m². Queensland’s classic project is raising a Queenslander and building in underneath — brilliant use of space, but check flood overlays and cyclone-region construction standards first. Demand is strong though: the HIA notes rapid population shifts are encouraging more Queensland homeowners to add space to their family homes.
Money-Saving Tips for Your Extension
- Keep the footprint simple. Rectangles are cheaper than L-shapes and wraparounds. Every corner, junction and roof valley adds labour and materials.
- Minimise plumbing moves. Group new wet areas near existing plumbing stacks. Running new drainage across the house is one of the fastest ways to inflate a quote.
- Get three detailed, like-for-like quotes. Give every builder the same plans and finish schedule, or you’re comparing apples to oranges.
- Consider the CDC path. If your design can meet complying development standards, you’ll save months and thousands in consultant fees compared with a full DA.
- Stick to standard sizes. Custom-sized windows, doors and joinery cost more and take longer. Standard modules keep the budget (and the timeline) in check.
- Lock in finishes before the build starts. Variations mid-build are where budgets go to die — builders charge a premium for changes once work is underway.
- Protect your contingency. Budget 10–15 per cent for surprises and don’t spend it on finish upgrades in week one. Old houses hide things.
- Run the numbers first. Before you talk to a builder, use our free renovation tools to sanity-check what your project should cost.
Frequently Asked Questions
How much does a 40m² extension cost in Australia?
At 2026 ground-floor rates of roughly $3,000–$4,500/m², a 40m² extension typically lands between $120,000 and $180,000 for the build itself, before fit-out like kitchens and bathrooms. A second storey of the same size would more likely run $130,000–$220,000.
Is it cheaper to extend or knock down and rebuild?
Per square metre, rebuilding is often cheaper ($2,400–$3,800/m²) because there’s no existing structure to work around. But the total is usually far higher — knockdown rebuilds commonly run $480,000–$950,000. Extending wins for modest additions; rebuilding wins when the existing house is in poor shape or you want far more space.
Do I need council approval for a house extension?
Almost always, yes. Most extensions need either a development application (DA) through your local council or a complying development certificate (CDC) if the design meets set standards. Always confirm with your council before you commit to a builder.
How long does a house extension take?
Allow four to seven months for a ground-floor extension and six to ten months for a second storey, from slab to handover. Add two to four months on top for design, engineering and approvals before construction starts.
Does a house extension add value to your home?
Generally yes, as long as the cost stays in line with your suburb’s price ceiling. Overcapitalising is the real risk — a $400,000 extension on a $700,000 house in a $800,000 street rarely pays for itself. For a suburb-by-suburb sense of what renovations return, see our renovation costs guide for 2026.