What common projects cost in Melbourne
Five typical projects, worked out with the calculator. Each assumes mid-range finishes, an architect from start to finish and a house of unknown age, unless it says otherwise. Choose one to load it into the calculator, then change the answers to match your house.
The whole project includes contingency, design and consultant fees, permits, landscaping and furnishings. All figures include GST.
Why it doesn't start with square metres
A square metre of hallway and a square metre of ensuite are completely different things. Two houses with the same floor area can differ by hundreds of thousands of dollars, and the reasons are almost never the size. So floor area is only one of the questions here, and the rate it uses for an extension leaves the kitchens and bathrooms out. They're counted on their own, because that's where the money goes. I've written more about why per-square-metre figures mislead.
What it asks about, and why
- Wet rooms. I allow $30,000–50,000 for each kitchen or bathroom for a like-for-like update with the plumbing left where it is. A laundry and a powder room together count as one. Moving the plumbing adds more, and on a concrete slab it adds a lot.
- The age of the house. It sets the contingency: 5–10% for a house built after 1980, 10–15% for a post-war house, and 15–20% before 1945, or wherever nobody knows what's behind the walls.
- Access. If a small excavator can't get down the side, everything is dug by hand or lifted over. That adds 3–15% to the build.
- Finishes. Builders price the laying of a tile, not just the tile. Custom joinery, shadow-line plaster and fiddly junctions all add hours on site.
- Everything outside the building contract. Design and consultant fees, permits and levies, landscaping, blinds and furniture, and rent if you move out while the work happens. Not sure whether you'll need a planning permit? Check your address.
Your construction budget is the smaller number
The number you give a builder isn't the total you have to spend. It's what's left once fees, permits, the extras and contingency come out, and that's usually a fifth to a third less. The calculator shows both, so you can be open with builders about the construction budget from the start. It gets you better advice than keeping it secret.
What this calculator can't see
Your house. Tired stumps, original wiring, asbestos and termite damage only show up when someone looks. Tick what you already know about; the contingency is for the rest.
Your site. Slope, poor soil, big trees, easements, and flood or bushfire controls can all change the number.
The design. A simple box and a complex one of the same size are priced very differently. The ranges here are wide for that reason.
Tender day. When builders are busy, prices go up. The only number to make decisions with is a detailed, itemised price against drawings, with the builder's exclusions and assumptions listed.
Questions people ask
How much does it cost to renovate a house in Melbourne in 2026?
It depends far more on wet rooms, the age of the house, access and finishes than on floor area. As a guide, with design, permits and contingency included, a kitchen and bathroom renovation with no extension comes to about $99,000–190,000, and a 25 m² rear extension with a new kitchen, bathroom and laundry about $215,000–400,000.
How much does a rear extension cost in Melbourne?
Allow about $3,000–4,500 per square metre for the extension itself at mid-range finishes, plus $30,000–50,000 for each kitchen or bathroom in it. A 25 m² extension with a new kitchen, bathroom and laundry has a construction budget of about $150,000–245,000, and comes to about $215,000–400,000 once fees, permits, contingency and the extras are added.
How much does a second-storey addition cost in Melbourne?
Upstairs floor area costs more than ground floor: about $4,000–6,000 per square metre, plus $25,000–60,000 for the stair and the structure that carries it through the house, plus the wet rooms. A 60 m² upstairs addition with two bathrooms has a construction budget of about $325,000–535,000, or $400,000–720,000 for the whole project.
What costs are there besides the builder's price?
Design and consultant fees (architect, structural engineer, building surveyor, land surveyor, soil test, energy rating), permit and lodgement fees and the building permit levy, contingency, landscaping, window furnishings and anything supplied by the owner, and rent if you move out during the works. Together they often take a fifth to a third of the total.
How much contingency should I allow for a renovation?
At least 10% on an older house, and 15–20% where the services and structure are unknown, such as a house from before 1945 that hasn't been touched in decades.
How much should I allow for a kitchen or bathroom?
As a rule of thumb, $30,000–50,000 per wet room for a like-for-like update with the plumbing left where it is, in Melbourne in 2026. Count a laundry and a powder room together as one. Moving the plumbing, especially through a concrete slab, costs more.