Second storey
How much does a
second storey cost
in Melbourne?
Between $470,000 and $640,000 for a typical 40 to 55 square metre addition with one new bathroom, on an inner-suburb house built before 1940. Here is where that number comes from, and the four things that move it most.
The short answer
| Scenario | Assumptions | Range |
|---|---|---|
| Modest addition, outer suburb | 40 m², standard finish, post-1990 house, clear access | $255k – $345k |
| Typical inner-north addition | 55 m², mid finish, pre-1940 house, one bathroom | $445k – $605k |
| Heritage terrace, restricted access | 40 m², mid finish, overlay, no vehicle access | $470k – $640k |
Why it costs more than a ground-floor extension
A ground-floor extension puts new structure on new footings. A second storey puts new structure on a house that was never designed to carry it, which is where the extra money goes.
The existing house has to carry it
Footings, stumps and wall framing usually need upgrading before anything goes on top. On pre-war timber stock this is close to universal, and it is invisible work you will never see once it is finished.
The roof comes off
The house is open to weather for a period. Temporary roofing, protection and the risk of a wet week are all priced in, and none of it adds a square metre of living space.
The stair eats downstairs
A staircase takes roughly four to six square metres out of your ground floor and often forces a reconfiguration of rooms you were not planning to touch.
You may need to move out
Second-storey work is more disruptive than a rear addition. Temporary accommodation and storage are excluded from every published rate, including ours.
What the published rates leave out
Published square-metre rates cover the basic shell and roofline. Applied straight, they will understate a real project by a wide margin. The items below sit outside them and have to be added.
| Item | Why it is separate | Typical |
|---|---|---|
| New bathroom or ensuite | Wet areas need fittings and waterproofing the shell rate does not include | $17.5k – $35k |
| Structural upgrade below | Work to the existing house, not the new floor | $26k typical pre-1940 |
| Professional fees and permits | Architect, engineer, surveyor, permit levy, energy assessment | 25% |
| Contingency | The most common overrun is undisclosed structural damage | 12% |
Planning and approval
A second storey is far more likely to need a planning permit than a ground-floor rear addition, because it is visible from the street and it affects overlooking and overshadowing of neighbours. In a heritage overlay, expect the design to go through more iterations before it is lodged. Building permits in Victoria are issued by a registered building surveyor you appoint, not by the council — the council's role is planning, which is a separate step.
Get an indicative range
Second-storey addition is already selected. Eight questions, and you will see every line of the calculation.
Common questions
Is a second storey cheaper than moving?
Often, in higher-value suburbs. Stamp duty and agent fees on an upsized purchase can run well past $100,000 before you have gained a single room. But the comparison depends entirely on your suburb's price ceiling — spending $600,000 on a house that will not resell above the street's top price is how people lose money renovating.
Can any house take a second storey?
Most can, with enough structural work. The real question is what that work costs, and the answer sits under the floor. An engineer's inspection of the footings and subfloor before you commit to a design is the cheapest money you will spend on the project.
How long does it take?
Design and approval commonly run six to twelve months before construction starts, longer in a heritage overlay. Construction itself is typically six to nine months. The approval phase is where most timelines slip.
Do I need to move out?
Usually for at least part of it, particularly while the roof is off. Budget for it separately — no published cost guide includes temporary accommodation, and ours does not either.
When you are ready to build
AE Index is not a building company. When a project is ready to be priced properly, we pass it to a builder from our verified network — who will walk the site, inspect what is under the floor, and put a fixed price in writing. We are paid a fee by them on work that proceeds, and you are under no obligation to use them.
Plenty of directories call their builders trusted without saying what that means. Ours means five specific things:
- Current domestic builder registration, confirmed with the Victorian Building Authority
- Domestic building insurance current and sighted
- Two completed projects contacted directly — not supplied testimonials
- Fixed-price contracts with a written variations policy
- Re-checked annually, and removed from the network on any lapse
The sensible order is estimate first, referral second. Run the numbers, decide whether the project is viable, and only then talk to a builder.
Last updated 28 July 2026