Second Storey Extension Cost 2026: What Going Up Actually Costs
Summary
The short version. A second storey in 2026 lands between $3,200 and $6,500 per square metre of new upper floor in the quotes we see, which puts a 70 square metre addition somewhere between $265,000 and $470,000 by the time the roof, structure, stair, and fitout are done. The upper floor is the straightforward half. The ground floor is where the money goes: strengthened footings, steel over existing openings, a stair that eats a bedroom, and rent somewhere else for six to nine months. Consultants and documentation add $14,000 to $45,000 before a single roof tile comes off. Approval takes three to six weeks on a complying pathway and four to seven months if council is assessing overshadowing with an unhappy neighbour on the file. Spend money on geotechnical and structural advice before you fall in love with a floor plan, because that advice decides whether the project is worth doing at all.
Table of Contents
Most second storey enquiries we receive arrive with a number already attached. The owner has found a per-square-metre figure online, usually sitting near $2,800, multiplied it by the 70 or 80 square metres they want upstairs, and landed on something close to $220,000. Then the geotechnical report comes back, the structural engineer asks for a pier and beam solution under the existing lounge room, and the number moves by six figures.
That gap is not bad luck. It is the difference between building a floor and building a floor on top of a house that was never designed to carry one. A single-storey brick veneer from 1978 was engineered for its own roof and nothing else. Adding a storey means the footings, the wall frames, the lintels, and sometimes the slab all get reassessed against loads they have never seen.
So the honest range for 2026, across the four states we document in, is $3,200 to $6,500 per square metre of new upper floor. Sydney and Melbourne inner suburbs sit at the top. Regional Queensland and Tasmania sit lower, with the caveat that trade availability can push a regional job past a metro one. Those figures cover construction only. Consultants, approvals, and living elsewhere are separate.
What a second storey costs in 2026
We see the same three cost bands repeat across the jobs we draw. A modest addition of two bedrooms and a bathroom, roughly 55 to 65 square metres, with a simple gable roof and no planning complications, lands between $210,000 and $330,000 in construction. A typical four-bedroom-upstairs layout of 80 to 100 square metres with two bathrooms and a reworked ground floor runs $340,000 to $560,000. Anything involving a lift, a cantilevered deck, structural steel through the middle of the existing house, or heritage fabric goes past $600,000 and keeps going.
Per square metre, going up costs more than going out. The same 70 square metres added at ground level with its own slab usually comes in 15 to 30 per cent cheaper, because nothing above it has to be demolished and nothing below it has to be strengthened. People choose the second storey anyway, and usually for a reason no spreadsheet captures. They want to keep the backyard.
The timeline at a glance
Owner-builders tend to plan the construction period accurately and the everything-else period badly. The build is the part with a Gantt chart. The eleven months in front of it are the part where a family ends up paying rent on a house they cannot move back into yet.
Here is the shape of a second storey project, based on the jobs we document and the feedback we get from clients once they are through it.
| Stage | Realistic duration | Typical spend at this stage | What gets underestimated |
|---|---|---|---|
| Feasibility, survey, geotechnical | 3–6 weeks | $3,500–$12,000 | That the geotech can kill the project outright |
| Concept design and client revisions | 4–8 weeks | $2,500–$7,000 | Three rounds of changes is normal, not slow |
| Structural engineering and consultants | 4–8 weeks (overlaps design) | $6,000–$22,000 | Engineering often forces a design rework |
| Construction documentation | 3–6 weeks | $6,000–$18,000 | Documentation depth drives quote accuracy |
| Approval (complying pathway) | 3–6 weeks | $3,000–$6,500 | Requests for further information |
| Approval (council assessment) | 4–7 months | $5,500–$16,000 | Neighbour objections and re-notification |
| Tender, contracts, and builder selection | 4–8 weeks | Nil to $2,000 | Good builders are booked 4–6 months out |
| Construction | 5–9 months | The rest of it | Wet weather while the roof is off |
Add it up honestly and a second storey is a 14 to 24 month commitment from first phone call to moving back in. We have seen faster. We have also seen a Melbourne job take 31 months because an overshadowing objection went to VCAT.
Every stage, and what it costs you
The cost of a second storey is not one number. It is about forty numbers, and the order you spend them in matters more than the total. Spending $9,000 on investigation before spending $12,000 on documentation is how you avoid throwing both away.
Stage 1: Survey, geotechnical, and the structural reality check
Before anything gets drawn, you need to know what is under the house and what is in the walls. A detail and level survey costs $1,400 to $3,800 depending on block size and slope. A geotechnical investigation with two or three boreholes runs $2,200 to $5,500. If the existing footings need exposing, add $1,500 to $4,000 for excavation and inspection. A second storey is the project where skipping the survey hurts most, which is why we’ve written separately about why a professional land survey matters before any design work starts.
We got this wrong early on. A client in the Hills district wanted to skip the geotech to save $2,800, and we documented a concept over an existing brick veneer on what we assumed was a standard reactive clay site. The engineer came back needing underpinning to 1.8 metres across two thirds of the perimeter. That added close to $55,000 and a design change to shift the upper floor footprint away from the worst of it. Two weeks of our drafting went in the bin. The lesson was cheap compared to what it could have been, and we have not documented a second storey without geotechnical input since.
Stage 2: Concept design and documentation
Concept design for a second storey costs more than a ground-floor addition because the constraints are tighter. Every window position gets tested against overlooking. Every wall wants to land on something that can carry it. Concept and design development typically runs $2,500 to $7,000, and full construction documentation, the drawings a builder actually prices and builds from, runs $6,000 to $18,000 depending on complexity and state requirements.
That is the line item people try hardest to cut, and it is the one that pays for itself. Thin drawings produce wide quotes. We regularly see three builders price the same thin drawing set with a $140,000 spread between them, because each one guessed differently about what was not shown. Most of those gaps come from the same handful of drafting mistakes owner-builders make, and every one of them gets more expensive when the drawing is of a second storey.
Stage 3: Engineering and the rest of the consultants
Structural engineering for a second storey is not the $2,000 exercise it is for a carport. Expect $4,500 to $12,000, higher if steel transfer beams are needed through the existing ground floor. On top of that, the list varies by state and site. Energy assessment (BASIX in NSW, NatHERS elsewhere) runs $450 to $1,200. Upstairs glazing and insulation choices move the rating more than most people expect, and our guide to 7-star energy ratings for owner-builders explains how.
A shadow diagram package is $800 to $2,500. A bushfire attack level assessment, where required, runs $1,200 to $3,500.The assessment is the cheap part. The rating then sets your window, cladding, and roof specification, and our breakdown of BAL construction costs shows what each level adds.
A town planner, if you are heading into a discretionary or merit assessment, runs $3,000 to $9,000 and is usually worth every dollar.
Stage 4: Approval
This is where the four states diverge, and where the advertised timelines stop meaning much.
In NSW, some two-storey alterations and additions qualify for a Complying Development Certificate under the Codes SEPP, which is a three to six week pathway through a private certifier at $3,000 to $6,500. The criteria are strict on height, setbacks, landscaped area, and privacy. Miss one and you are in a Development Application with council instead, which is $5,500 to $16,000 all in and four to seven months realistically.
In Victoria, a building permit is certain and a planning permit is likely, because Clause 54 of the planning scheme tests overlooking, overshadowing, and neighbourhood character on a second storey more aggressively than on anything else you can build. Overlays make it worse. If an objection lands and you end up at VCAT, add six to twelve months and $15,000 to $45,000 in legal and expert costs.
In Queensland, whether you need a development approval depends on your local plan. Brisbane’s pre-1947 character overlay is the one that catches people, because it can restrict what you do to the roof form and the front of the house even when the height is compliant. Building work is assessed against the Queensland Development Code either way.
In Tasmania, the relevant planning scheme provisions and the Director’s Determinations decide whether your work is permitted or discretionary, and wind and snow loading in the highlands changes the structural cost before you get to planning at all.
If you’re running the job yourself, the owner-builder permit requirements in your state sit on top of the planning and building approvals and need to be in place before work starts. We have said this to enough clients now to be confident in it. Do not commit to a builder’s start date until you hold the approval in your hand.
Stage 5: Construction
Once the roof comes off, the clock is honest. A straightforward second storey runs five to seven months. Add a reworked ground floor, a new kitchen, or a difficult site access and it becomes seven to nine. The first three weeks are the highest risk period in the entire project, because that is when the existing house is open to the weather under a temporary roof. Temporary weatherproofing costs $8,000 to $30,000 and it is not optional.
Before you commit to a number, write it all down. We built the owner-builder budget checklist so you can price the whole project instead of the pretty part. It covers consultants, approvals, temporary accommodation, storage, and the contingency most people leave out. If you are not sure whether your work needs a planning approval or just a building permit, run it through the permit checker first.
The line items that wreck second storey budgets
Per-square-metre pricing is the most misleading number in Australian renovation, and the industry keeps using it because it makes a large project sound small. Pricing a second storey by the square metre is like pricing your grocery shop by the kilo. A kilo of potatoes and a kilo of salmon are not the same shop, and neither are 70 square metres of bedrooms and 70 square metres of bedrooms sitting on new steel over a sixty-year-old brick house.
These are the items that sit outside most advertised figures and inside almost every final invoice.
| Line item | Typical 2026 range | Notes |
|---|---|---|
| Roof demolition, disposal, and asbestos handling | $12,000–$40,000 | Asbestos-cement sheeting alone can add $8,000–$25,000 |
| Temporary roof and weatherproofing | $8,000–$30,000 | Priced weekly; wet weather costs you twice |
| Scaffolding | $7,000–$22,000 | Usually 16–30 weeks of hire |
| Footing strengthening or underpinning | $15,000–$75,000 | Entirely dependent on the geotech |
| Structural steel and transfer beams | $18,000–$60,000 | Includes propping the existing structure |
| New roof structure and covering | $32,000–$85,000 | Larger footprint than the one you removed |
| Internal staircase | $9,000–$28,000 | Plus the ground-floor room you lose to it |
| Upstairs bathroom, fully tiled | $28,000–$55,000 | Waterproofing over a timber floor, done properly |
| Ground-floor make-good and repaint | $18,000–$45,000 | Cracking, ceiling replacement, cornice, flooring |
| Temporary accommodation | $22,000–$60,000 | Six to nine months of rent plus a bond and storage |
| Contingency | 12–18% of contract sum | Not a luxury on a retrofit |
The staircase deserves its own paragraph. It costs $9,000 to $28,000 to build, and it also consumes eight to twelve square metres of your existing ground floor, usually from the hallway, a bedroom, or the living area. We have watched a client add four bedrooms upstairs and lose one downstairs, for a net gain of three. Draw the stair first. Everything else on the ground floor arranges itself around it.
What Draftee does. We prepare the concept design, coordinate the consultants, and produce the construction documentation your builder prices and your certifier assesses. We draw the plans, we don’t sell buildings. That means we have no incentive to talk you into a bigger second storey, a fixed-price package, or a product line with our name on it, and no reason to shade a feasibility answer to protect a sale. If the geotechnical report says your house cannot carry a second storey economically, we would rather tell you in week three than in month nine.
What you can actually control
Very little of a second storey budget is negotiable once the engineer has signed the drawings. Almost all of it is negotiable before that, which is the opposite of how most owner-builders spend their attention.
Keep the upper floor inside the existing footprint wherever you can. Every metre the new floor extends past a supporting wall below becomes a cantilever or a new footing, and either one costs $4,000 to $15,000 more than landing on what is already there. Stack the wet areas. Putting the upstairs bathroom above the downstairs bathroom or laundry saves $6,000 to $14,000 in plumbing, and it keeps the noisy pipes out of the middle of your bedrooms.
Keep the roof simple. A hip and valley roof with four changes of pitch costs 25 to 40 per cent more than a gable or skillion covering the same area, and it leaks in more places over twenty years. Decide your finishes before the drawings go out to tender, because a $40,000 allowance for tapware and tiles becomes a $75,000 variation once someone walks into a showroom.
Then hold the contingency. Twelve per cent minimum, fifteen if the house is older than 1980, and do not touch it for a nicer benchtop in month two.
Ready to draw?
If you are weighing up a second storey, the useful next step is not a builder’s quote. It is a clear-eyed read on what your existing house can carry and what the approval pathway looks like in your council area. That is the work we do first.
Tell us about your block and we will come back with the documentation scope, a fixed fee, and an honest view on the approval pathway for your site. We work with owner-builders across NSW, VIC, QLD, WA and TAS.
Questions we get asked about second storey costs
Sometimes, and the crossover point is closer than people expect. A 90 square metre second storey with significant ground-floor rework can reach $520,000, and a full knock-down rebuild of a four-bedroom house in the same suburb might be $650,000 to $850,000 for a brand new dwelling with no retrofit compromises and no 1970s wiring.
If your existing house is structurally sound, well positioned on the block, and you only need bedrooms, going up usually wins. If the ground floor layout is bad, the footings are marginal, and you are rewiring and replumbing anyway, run both numbers properly before you decide.
On a wide enough block, there’s sometimes a third answer worth pricing: building two houses on one block. We have had two clients abandon a second storey at the feasibility stage and rebuild instead. Both were happier for it.
Usually, but the slab and its footings decide the cost. Slab-on-ground houses built after roughly 1990 to engineered footing standards often carry a second storey with localised thickening and new pad footings under the new load paths. Older slabs, unreinforced edge beams, and reactive clay sites are where the figure climbs. We have seen slab retrofits handled for $18,000 and we have seen them cost $90,000 with piers drilled through the existing floor. Nobody can tell you which one you have from the kerb. The geotechnical investigation and the structural engineer’s assessment are the only honest answer, and together they cost $7,000 to $17,000. That is the cheapest money you will spend on the project.
Concept design through to construction documentation for a second storey generally runs $8,500 to $25,000 across the market, depending on the size of the addition, how much of the ground floor changes, and which state you are in.
The spread mostly reflects documentation depth. A set that shows every junction, every beam, and every bathroom setout costs more to produce and saves more in the build, because the builder is pricing what is drawn instead of pricing risk. It’s also why the cheapest drafting quote is rarely the cheapest outcome on a job this size.
We quote fixed fees for defined scopes so you know the number before we start, and we itemise what sits outside our scope, which is usually the engineering, the energy assessment, and the certification fees.
In NSW and Victoria, a neighbour objection on a second storey almost always concerns privacy or overshadowing, and both are assessable matters that council must consider. An objection does not stop a compliant design, but it costs you time. Expect an additional six to sixteen weeks of assessment, and possibly a request for amended plans with obscured glazing, raised sill heights, or a reduced upper-floor footprint. If it escalates to the Land and Environment Court in NSW or VCAT in Victoria, budget $15,000 to $45,000 and six to twelve months. The best defence is boring. Design inside the setbacks, keep the habitable-room windows off the shared boundary, and produce shadow diagrams that show compliance rather than arguing about it.
For a second storey, yes, in almost every case. The roof comes off the entire section you are building over, the ceilings below come down, and the house is unweatherproofed for weeks.
We have had clients who stayed by isolating half the house behind a temporary wall. It worked twice and it was miserable both times. Budget $22,000 to $60,000 for six to nine months of rent, bond, removalists, and storage.
Also check your insurance, because most home policies change or lapse during major structural work and you will need a contract works policy from the builder or from yourself if you are owner-building. Our owner-builder insurance guide covers which policies you need and when they have to be in place.
Three places, in this order. Footing and structural work that the geotechnical report exposed after the design was locked in. Ground-floor make-good, which people forget entirely and which runs $18,000 to $45,000 in cracking repairs, ceiling replacement, cornice, and repainting. And time, because temporary roofing, scaffolding, and rent are all priced by the week and a two-month delay is $12,000 to $20,000 in holding costs alone. None of those three appear in a per-square-metre estimate. All three appear in the final account.
Continue Your Research
Knock Down Rebuild Cost 2026: What the Whole Job Actually Costs
Sloping Block House Design: Cost, Approvals, and What the Fall Decides
The Importance of Professional Land Surveys: Why the Fence Isn’t the Boundary
Draftee provides architectural drafting and documentation services. We are not lawyers, builders, engineers, or certifiers, and nothing above is legal, financial, structural, or construction advice. Planning controls, building code provisions, and approval pathways change and vary between councils and states, so verify every regulatory detail with your local council, your certifier, or your registered building surveyor before you spend money. Structural feasibility for any second storey must be assessed by a qualified structural engineer on your specific site.
The figures in this article reflect quotes, consultant fees, and approval costs we have seen across our own projects as at early 2026. They are not a quote and they are not survey data. Construction pricing moves with trade availability, site conditions, and material supply, and a second storey is more exposed to site conditions than any other residential project type. Planning and building regulations differ by state and by council, National Construction Code editions and state variations are amended on cycles outside our control, and Tasmania has amendments to its planning provisions in progress at the time of writing.
Last updated and changelog
Last updated: 20 September 2026
Changelog:
– 20 September 2026: Initial publication
