House extension cost in Melbourne 2026

A house extension in Melbourne costs roughly $4,500 to $7,500 per square metre inc. GST in 2026 — so a typical 40 m² rear extension lands somewhere between $179,000 and $291,000 depending on finish, site access and how old the house is.

That's a wide band, and the spread is the whole story. Two identical-looking extensions in Northcote and Narre Warren can be $80,000 apart before anyone picks a tap. Reactive clay, a heritage overlay, a tight side setback, or the simple fact that you're living in the house while it's being built — each of those quietly moves the number.

This guide breaks the cost down the way a builder actually prices it: a base rate per square metre, then a stack of multipliers on top. You'll get real ranges by size and finish tier, what the council paperwork costs, what usually isn't in the quote, and how to sanity-check the numbers you're given. If you want a ballpark for your own job right now, the Leadkit builder and renovation calculators run the same maths in about 30 seconds.

Last updated: August 2026.

Key takeaways

• A single-storey rear extension in Melbourne costs about $4,500–$7,500 per m² inc. GST in 2026, which puts a 40 m² addition at roughly $179,000–$291,000.
• A second storey extension costs more per square metre than a ground-floor addition — expect around 5% extra for the double-handling alone, plus structural work to the floor below.
• Finish tier is the single biggest lever you control. Moving from builder's standard to premium fixtures adds roughly 60% to the build cost on the same footprint.
• Living in the home during the build typically adds 15–20% — on a $209,000 extension that's around $36,000 for dust walls, staged trades and slower progress.
• A pre-1980 Melbourne home adds around 25% to the base build rate because asbestos, lead paint and original wiring are near-certainties, not surprises.
• Council approvals, design fees and site costs sit outside the per-square-metre rate. Budget a separate allowance of about $5,500 for the planning and building permit stack.

What this guide covers

• How much does a house extension cost in Melbourne in 2026?
• What does a rear extension cost in Victoria?
• How much does a second storey extension cost in Melbourne?
• What drives home extension prices in Melbourne up or down?
• Council permits, planning and the paperwork nobody budgets for
• What isn't in the builder's quote
• How to compare Melbourne extension quotes properly
• Frequently asked questions

How much does a house extension cost in Melbourne in 2026?

A ground-floor house extension in Melbourne costs $4,500–$7,500 per square metre inc. GST in 2026, with most mid-range projects landing near $5,200 per m². The table below models a single-storey rear extension on a home aged 10–30 years, with easy street access, a standard build timeline, structural work included and a $5,500 council allowance.

All figures inc. GST. Go luxury or architect-designed on the same 40 m² footprint and you're looking at closer to $413,000 — bespoke joinery and designer glazing roughly double the base rate.

Methodology: these ranges come from Leadkit's own builder and renovation quote calculator, which prices extensions at a $4,000 per m² base build rate before finish tier, property age, site access and timeline multipliers are applied, then adds 10% GST. Leadkit built and maintains that calculator, so this is our own rate data rather than a neutral third-party survey — we're showing you the model, not asking you to take it on faith.

This is a price indication only. Your tradie will confirm the final price after assessing the job.

Want a number for your actual floor plan? Run the free builder and renovation quote calculator — pick your extension size, finish and site conditions, and you'll get an itemised estimate emailed to you. No signup.

What does a rear extension cost in Victoria?

A rear extension cost in Victoria typically runs $4,500–$7,500 per square metre inc. GST, the same base band as metro Melbourne, but regional sites often add a travel and supervision loading of 5–10%. Geelong, Ballarat and Bendigo builders are pricing against a smaller subcontractor pool, so trade availability rather than materials tends to set the number.

Rear extensions are the most common shape of the job in Melbourne because they suit the housing stock. Victorian terraces, Edwardian weatherboards and Californian bungalows all share the same layout problem — good rooms at the front, a lean-to kitchen tacked on the back — so the fix is almost always to remove the rear and push out.

That's also why rear extensions carry hidden structural cost. Once you take out the back wall of a load-bearing weatherboard, you're into a steel beam, new footings and often re-stumping the section you kept. Re-stumping alone commonly runs $15,000–$25,000 on an older Melbourne home, and it's rarely in the headline quote.

Three site conditions push a Victorian rear extension toward the top of the band:

• Reactive clay soil. Much of Melbourne's east and north sits on highly reactive clay, which pushes your site classification — the AS 2870 rating (M, H1, H2 or P) that tells the engineer how much the ground will move — up to H1 or H2. That means deeper footings and more steel in the slab.
• No truck access. Terraces in Fitzroy, Carlton and Richmond often have no side gate wide enough for a bobcat. Every cubic metre of spoil goes out by wheelbarrow, and that adds around 25% to the build.
• Heritage overlay. Anything in a heritage overlay needs the rear addition set back and hidden from the street, which usually means a more complex roof form and custom windows.

For a like-for-like comparison across the country, our national house extension cost guide shows how Melbourne rates sit against Sydney, Brisbane and Perth.

How much does a second storey extension cost in Melbourne?

A second storey extension in Melbourne costs approximately $187,000 for a 40 m² addition at builder's standard finish, rising to about $604,000 for an 80 m² premium build, inc. GST. Going up adds roughly 5% per square metre over the equivalent ground-floor addition purely for the extra complexity of working at height.

This is a price indication only. Your tradie will confirm the final price after assessing the job.

The trap with second storey extension cost in Melbourne isn't the new floor — it's the old one. The existing house has to carry the load, and on a pre-1980 home that usually means underpinning (pouring new concrete beneath the existing footings so they can take the extra weight) or replacing stumps with steel posts and a new bearer layout.

You'll also lose the house for longer. A second storey typically means the roof comes off, so unlike a rear extension you generally can't live in it — factor 4–6 months of rent somewhere else into the real cost.

The upside is land. In suburbs where a knock-down rebuild is the alternative, going up avoids buying floor area you already own. If you're weighing the two paths, compare against our knock-down rebuild cost guide before you commit — the crossover point is closer than most people expect.

What drives home extension prices in Melbourne up or down?

Home extension prices in Melbourne are set by six multipliers applied to the base per-square-metre rate: finish tier, property age, site access, build timeline, whether you stay in the house, and whether you engage a designer. Here's what each one actually costs on a mid-range 40 m² extension priced at $209,000.

This is a price indication only. Your tradie will confirm the final price after assessing the job.

Two things stand out on that list. First, access costs as much as finish — a narrow Brunswick side passage can cost you as much as upgrading every fixture in the house. Second, the cheapest lever is the one nobody wants to pull: move out and give the builder an empty site.

Across the quote calculators in Leadkit's library, 28 of the 90 quote-style calculators ask about site access before they price anything — because for trades that carry materials onto a site, access is a first-order cost input, not a footnote. Extension pricing is the clearest example of it.

If you're bringing a designer in, the architect design fee calculator prices that engagement separately so you can see the professional fees on their own line rather than buried in the build.

Council permits, planning and the paperwork nobody budgets for

Most Melbourne extensions need both a planning permit and a building permit, and the combined approvals stack typically costs around $5,500 before construction starts. That allowance covers the planning application, the building permit, and a planning consultant where the council requires one.

The planning side is where Melbourne gets specific. Extensions are assessed against ResCode (Clauses 54 and 55 of the Victorian planning provisions), which sets the rules for overshadowing, overlooking, setbacks and private open space. Push a two-storey addition too close to a southern boundary and you'll be redesigning the roof to keep your neighbour's north-facing windows in the sun.

You may also need a Report and Consent — a separate council approval required when you're building over an easement, reducing a setback below the standard, or altering stormwater drainage. It's a small fee but a long lead time, and it's the single most common reason a Melbourne extension sits idle for six weeks.

A few Victoria-specific rules worth knowing before you sign anything:

• Domestic building contracts over $10,000 must be in writing and carry the mandatory warranties set out under Victorian law. Consumer Affairs Victoria publishes the required contract terms.
• Domestic building insurance is required for work above the state threshold (currently $16,000), and your builder must supply the certificate before taking a deposit. It protects you if they die, disappear or become insolvent.
• Your builder must be registered. Check the practitioner register at the Victorian Building Authority before money changes hands — registration status is public and takes two minutes to verify.
• Deposits are capped. For domestic building work, the maximum deposit is limited by law; if someone asks for 30% up front, that's a red flag, not a negotiation.

For broader cost context, the Housing Industry Association and the Australian Bureau of Statistics both publish residential construction and building approvals data that tracks where Victorian build costs are heading quarter to quarter.

What isn't in the builder's quote

The most common budget blowouts on Melbourne extensions are the items that sit outside the construction contract entirely: site preparation, service upgrades, temporary accommodation and the finishing trades at the end. A fixed-price build contract is fixed on the scope it names, not on your project.

Watch for these:

• Site costs and soil. If the report comes back H2 or P classification, the footing design changes and so does the price. Get the soil test done before you sign, not after.
• Service upgrades. A bigger house often needs a switchboard upgrade, a larger water meter, or a relocated sewer connection. Melbourne Water asset protection applies if you're building near a sewer main.
• Re-stumping and levelling. Extending off an existing floor means both halves need to be on the same plane. On an older weatherboard, they rarely are.
• Landscaping and reinstatement. The builder leaves you a finished box. Paths, drainage, the lawn the excavator destroyed and the fence the crane took out are yours.
• Temporary accommodation. Four to six months of rent, plus storage, plus a second set of utility connections.
• Asbestos removal. In pre-1987 Melbourne homes, eaves, wall sheeting and old vinyl are all candidates. Removal is licensed work under Safe Work Australia codes and priced separately.

A pre-build inspection is cheap insurance against most of these. Pricing one takes a minute with the building inspection quote calculator, and finding out about the stumps before you're contractually committed is worth many times the fee.

How to compare Melbourne extension quotes properly

Compare extension quotes on scope and inclusions first, price second — a $40,000 gap between two builders almost always means they're pricing two different jobs. Ask every builder to quote the same written scope, or you're comparing nothing at all.

Here's the checklist we'd use:

1. Get three quotes, all against one scope document. Write down the finish level, the fixtures, the glazing and who does the landscaping.
2. Ask what allowances are in there. A "$3,000 kitchen allowance" is a placeholder, not a kitchen. Allowances are where cheap quotes hide.
3. Check the provisional sums. Site costs, soil and service connections are often provisional. Ask what happens when they're exceeded.
4. Confirm registration and insurance. Registration number, domestic building insurance certificate, public liability. In writing.
5. Read the variation clause. How much notice, what markup, and who approves it. This clause decides how much the last 20% of your build costs.
6. Ask for a build programme with dates. A builder who won't commit to a schedule usually can't.

Across the 90 quote-style calculators in Leadkit's library, 54 carry a minimum job fee — because below a certain size, mobilising a crew costs more than the work itself. That's why a 15 m² extension rarely comes in proportionally cheaper than a 40 m² one: the setup, the permits and the supervision barely move.

One honest observation from the rate data: when we model builder renovation quotes, the line homeowners consistently underestimate isn't materials — it's the multipliers. People budget carefully for the kitchen and then get caught by access, age and living on site, which together can add more than the entire finish upgrade they agonised over.

And if the extension is really a kitchen and living rebuild in disguise, price it as one — the individual trade calculators will get you closer than a single whole-of-project number.

Frequently asked questions

Q: How much does a 40 m² house extension cost in Melbourne?

A: A 40 m² house extension in Melbourne costs roughly $179,000 at builder's standard finish, $209,000 mid-range and $291,000 with premium fixtures, all inc. GST. That models a single-storey rear addition on a home aged 10–30 years with easy street access, structural work included and a $5,500 council allowance. Older homes, tight access or living on site during the build push it higher. You can model your own combination with the builder and renovation quote calculator above. This is a price indication only — your builder will confirm the final price after inspecting the site.

Q: Is it cheaper to extend out or build up in Melbourne?

A: Extending out is usually cheaper per square metre than building up — a second storey adds around 5% for working at height, plus structural work to the existing house and often underpinning. Going out costs you land and open space instead, and on a small inner-Melbourne block you may not have either. The rule of thumb: if your block has room behind the house and you're not fighting a heritage overlay, extend out. If you're on a narrow terrace block in Fitzroy or Prahran, up is the only real option, and you should budget for the roof coming off and four to six months of rent.

Q: Do I need a planning permit for a house extension in Victoria?

A: Most Victorian extensions need a building permit, and many also need a planning permit — it depends on your zone, any overlays on the title, and whether the design meets ResCode standards for setbacks, overshadowing and overlooking. A single-storey rear addition on a standard suburban block in a general residential zone can sometimes proceed on a building permit alone. Anything two-storey, in a heritage overlay, or close to a boundary almost always triggers a planning permit. Check your property report on the council's planning portal first, and budget around $5,500 for the whole approvals stack.

Q: What are home extension prices in Melbourne per square metre in 2026?

A: Home extension prices in Melbourne run about $4,500–$7,500 per square metre inc. GST in 2026 for an all-in figure that includes the build, structural work and a council allowance. The base construction rate before multipliers sits near $4,000 per m². Where you land in that band comes down to finish tier, how old the house is, whether a truck can get to the site and how fast you need it done. Luxury and architect-designed builds sit above the band entirely, often past $10,000 per m².

Q: How long does a house extension take in Melbourne?

A: Most Melbourne extensions take 4–8 months on site, plus 3–6 months beforehand for design, permits and the builder's schedule. A single-storey rear addition of 30–40 m² is typically 4–5 months of construction. A second storey runs 6–8 months because the roof comes off and the existing structure has to be reinforced first. Planning permit assessment adds 8–16 weeks on its own, and a Report and Consent for an easement or setback can add another six. Rushing it costs money — an urgent timeline adds around 15% to the build.

Q: Does an extension add more value than it costs in Melbourne?

A: Sometimes, but it's not automatic. Adding a fourth bedroom and a second bathroom to a well-located three-bedroom home in an established Melbourne suburb tends to return well, because you're moving the property into a different buyer bracket. Spending $400,000 on a luxury addition in a suburb with a median well below the resulting value rarely does. Before you commit, check comparable sales for the finished configuration in your own suburb — not the one next door — and remember that stamp duty, agent fees and moving costs are what you're really comparing an extension against. Our Victorian stamp duty guide sets out the cost of the alternative.

Q: What is a site classification and why does it change the price?

A: A site classification is the AS 2870 rating — M, H1, H2 or P — that a soil test gives your block, and it tells the engineer how much the ground will move with moisture. Much of Melbourne's east and north sits on highly reactive clay, which commonly lands an H1 or H2 classification and requires deeper footings, more reinforcement and a stiffer slab design. The difference between an M-class and an H2-class footing design on a 40 m² extension can be tens of thousands of dollars. Get the soil test done before you sign a fixed-price contract, because if the site cost is a provisional sum, that variation is yours to pay.

Q: Can I live in the house during an extension?

A: You can for most single-storey rear extensions, but it costs you about 15–20% on the build. The builder has to erect dust walls, stage the trades around your living areas, protect finished surfaces and work shorter hours. On a $209,000 extension that premium is around $36,000 — often more than renting a place nearby for the duration. For a second storey it's usually not an option at all, because the roof comes off. Price both scenarios before you decide; the "saving" from staying put frequently disappears once the premium is on the table.

Final tips before you commit

Get the soil test and the building inspection done before you sign, not after. Every expensive surprise on a Melbourne extension — reactive clay, rotten stumps, asbestos in the eaves, a sewer easement through the middle of your new living room — is knowable in advance for a few thousand dollars.

Then set your contingency at 15%, not 10%. On a $209,000 extension that's roughly $31,000 sitting in reserve. If you don't need it, you've got a landscaping budget. If you do need it, you've avoided the worst position in residential construction: out of money with the roof off.

And be honest about the finish tier before you brief anyone. Premium fixtures on the same footprint add around $82,000 to a 40 m² job. That's a legitimate choice — just make it deliberately at the start, rather than $30,000 at a time in the showroom halfway through.

Want an instant price estimate for your extension? Get your free quote estimate with Leadkit — pick your size, finish and site conditions and you'll get a full breakdown emailed to you in 30 seconds. Results are an indication only; your builder confirms the final price after assessing the job.

And if you run a building or renovation business yourself, you can embed the same calculator on your own site in 60 seconds — and turn the people pricing extensions at 11pm into leads with their contact details already attached.