Melbourne’s housing stock is well suited to extension and badly suited to being left alone. The city is full of compartmentalised cottages, bungalows and post-war homes with a dark rear kitchen, a disconnected back yard and one bathroom for four people. Adding thirty or forty square metres at the rear fixes all three, and costs less than the stamp duty on moving to a house that already has them.
This guide covers what Melbourne extensions cost in 2026, which approvals apply under Victoria’s two-permit system, and the design and structural realities specific to this city.
What Extensions Cost in Melbourne
New construction and extension work in Melbourne runs $2,700 to $5,100 per square metre in 2026, against $1,600 to $3,900 for reworking existing fabric. Adding area is the expensive option.
Typical whole-project figures:
- Small rear addition, 20 to 30 sqm — $70,000 to $145,000
- Medium ground-floor addition, 30 to 50 sqm — $130,000 to $240,000
- Large ground-floor addition, 50 to 70 sqm — $190,000 to $340,000
- Rear open-plan addition including a new kitchen — $150,000 to $300,000
- Second-storey addition, 60 to 90 sqm — $280,000 to $560,000
- Two-storey rear addition — $350,000 to $750,000
Inside those numbers
- Demolition and site preparation — $5,000 to $18,000
- Excavation and footings — $18,000 to $55,000, and higher than most cities because Melbourne’s reactive clay demands engineered footings
- Slab or subfloor framing — $15,000 to $40,000
- Structural frame and roof — $28,000 to $85,000
- Removing a load-bearing wall with a steel beam — $7,000 to $14,000, plus new stumps or footings under point loads in a stumped house
- Windows and external glazed doors — $15,000 to $55,000, and higher than other states because 7-star energy requirements push toward double glazing
- External cladding — $150 to $400 per square metre
- Roofing — $85 to $170 per square metre
- Services rough-in and fit-off — $16,000 to $42,000
- Internal linings, painting and joinery — $28,000 to $75,000
- New kitchen within the addition — $30,000 to $60,000
- Flooring — $70 to $200 per square metre
- Landscaping and making good — $10,000 to $45,000
Costs before construction
- Architectural or drafting documentation — $6,000 to $40,000
- Structural engineering — $2,500 to $6,000
- Soil report — $600 to $1,500, and essential
- Feature and level survey — $1,200 to $3,000
- Energy rating assessment — $400 to $1,200
- Building permit — $2,000 to $6,000
- Planning permit where an overlay applies — $1,500 to $5,000 in fees plus consultants
- Arborist report where trees are affected — $800 to $2,500
Allow $14,000 to $55,000 in pre-construction costs on a Melbourne extension.
Approvals: Victoria’s Two-Permit System
Melbourne extensions need a building permit from a registered building surveyor in essentially every case. Whether they also need a planning permit from council depends on overlays and zone provisions rather than the work itself.
You will likely need a planning permit where:
- A Heritage Overlay applies — common across inner Melbourne
- A Neighbourhood Character or Design and Development Overlay applies
- Flood controls apply — Land Subject to Inundation or Special Building Overlay, which affect more of inner Melbourne than people expect along old creek lines
- A Significant Landscape or Vegetation Protection Overlay applies and trees are affected
- The lot is under 300 square metres in certain residential zones
- The design departs from the state residential design standards on setbacks, height, site coverage, overshadowing, overlooking or private open space
A single-storey rear extension on a standard suburban Melbourne lot with no overlays, designed within the standards, frequently needs no planning permit at all. This surprises people, and it is the single biggest lever on your programme — the difference between a two-month approval and a nine-month one.
Check your overlays before you design. Free property reports for any Victorian address show zone and overlay information. See our full guide to Melbourne building and planning permits.
The Structural Reality: Reactive Clay and Stumps
This is where Melbourne extensions differ most from other cities.
Soil classification governs the footings
Melbourne’s basalt plains and clay soils produce highly reactive site classifications — commonly H1, H2 or E. A soil report costs $600 to $1,500 and determines the footing design, which in turn is one of the largest single line items. Engineered footings on an H2 site can cost $15,000 to $40,000 more than a standard slab on a stable site.
Joining new to old across moving ground
The junction between an existing stumped timber house and a new addition on a concrete slab is the most common source of extension defects in Melbourne. The two structures sit on different foundation systems and move differently — the old house rises and falls seasonally with the clay, the new slab does not.
The solutions:
- An articulation joint at the junction — a deliberate control joint through wall and ceiling allowing independent movement. Extensions built rigidly to old Melbourne houses crack, invariably.
- Matching the foundation system — building the addition on stumps or piers to match, so both move together. Increasingly common and often the better answer on a heritage cottage.
- Restumping the existing house first, so the old structure is stable before the new one is attached to it.
That last point matters enormously. Extending a house that needs restumping, without restumping it, means the new addition stays still while the old house continues to move. The junction will fail.
Second storeys on stumped houses
A timber cottage on timber stumps cannot carry another floor. Adding one generally requires replacing the entire subfloor structure with engineered footings and steel or concrete stumps, and often upgrading wall framing. This is why Melbourne second-storey additions frequently cost more than the equivalent work on a Brisbane or Perth brick home, and why an engineer’s assessment must come before any design work.
For more detail on this part of the project, see Prefabricated Second-Storey Additions: Crane Access and Module Connections.
Trees
On reactive clay, a mature tree near a proposed footing draws moisture and causes differential settlement. Removing one causes heave in the opposite direction as the soil rehydrates over several years. Either way an arborist and an engineer need to be involved, and root-sensitive footing design — piers and beams — may be required. Many Melbourne councils also protect trees under overlays or local law, and removal may simply be refused.
Extension Types That Work in Melbourne
The rear open-plan addition
The archetype: demolish the rear lean-to, add a single-storey volume with kitchen, dining and living, and open it to the back garden with glazed doors.
What determines success in Melbourne specifically:
- Northern orientation is close to everything. Melbourne has real winter, and a north-facing living space with correctly sized eaves is warm in June and shaded in January. A south-facing rear addition needs high-level or clerestory glazing on the north side, or it becomes an expensive cold room.
- Thermal mass. A concrete slab in a north-facing addition stores winter sun. In Melbourne’s climate this is worth real money in running costs, and it is free if you are pouring a slab anyway.
- Ceiling height. 2,700mm or higher transforms the space for modest additional cost.
- The junction. A deliberate threshold between old and new reads better than a blend, and it is where the articulation joint goes anyway.
- Glazing performance. Large glazed areas in Melbourne need double glazing to meet energy requirements and to be comfortable. Budget for it rather than being surprised by it.
The side extension
Where the block is wider than the house — common in middle-ring Melbourne — extending sideways adds width to narrow rooms. The constraint is side setback under the residential standards, and overlooking of the neighbouring property.
The bungalow rear extension
Melbourne’s interwar californian bungalows have generous proportions and a natural place to extend at the rear. Their solid brick construction carries load better than a weatherboard cottage, making second storeys more feasible, though the reactive clay still governs footings.
For more detail on this part of the project, see Renovating on Reactive Clay Soil: What to Discuss with Your Engineer.
The narrow single-fronted addition
Inner Melbourne single-fronted cottages are 3.6 to 4.5 metres wide on long narrow lots. Successful additions here often go two storeys at the rear with a light court or void cut into the plan, since building out consumes the only outdoor space.
The outdoor room
Cheaper than enclosed space and, with the right orientation and some weather protection, usable for much of the Melbourne year. See our guide to Melbourne decks and alfresco areas.
Energy Requirements
Victoria applies the National Construction Code energy provisions, requiring a 7-star NatHERS outcome for new dwellings along with a whole-of-home energy budget. For extensions, requirements generally apply to the new work, with the scope depending on the extent of alteration.
Practically, on a Melbourne extension this means double or high-performance glazing, insulation to specified R-values in walls, ceiling and floor, and efficient heating and hot water. Budget $10,000 to $30,000 for the energy-driven component, and treat it as an investment — Melbourne’s heating season makes it the part of the project you feel every day.
Timelines
- Design and documentation — 8 to 20 weeks
- Planning permit, where required — 8 to 36 weeks, longer with objections or VCAT
- Building permit — 2 to 4 weeks after complete documentation
- Tender and contract — 4 to 8 weeks
- Construction, single storey — 16 to 28 weeks
- Construction, second storey — 26 to 44 weeks
End to end: seven to twelve months for a single-storey extension with no planning permit, twelve to twenty months where a planning permit is required, and eighteen to thirty months for a second storey in a heritage overlay.
Melbourne’s winter adds a real constraint. Excavation, footings, framing and roofing all slow in June to September, and a project not at lock-up by late autumn will lose weeks. Where possible, schedule the wet-weather-sensitive stages for spring and summer.
Getting It Right
- Check overlays before design. This determines your timeline more than anything else.
- Get the soil report early. On Melbourne clay it drives the footing design and therefore the budget.
- Have an engineer assess the existing structure before contemplating a second storey.
- Restump first if the house needs it. Do not attach a new building to a moving one.
- Design for north. In this climate it is the difference between a room you use and a room you heat.
- Document thoroughly. Cheap drawings produce expensive variations.
- Tender to three builders on identical documentation. See our guide to vetting a Melbourne builder.
- Hold 15 to 20 per cent contingency. Extensions expose the existing house, and Melbourne’s housing stock always has something to say.
The Melbourne extensions people are happiest with years later share a pattern. They faced north, they sat on footings designed for the actual soil, they were joined to a house that had already been made stable, and the glazing was good enough that the room is pleasant in July as well as October.
Living Through an Extension in Melbourne
Whether you can stay depends on the work and on where the wet areas are — and on the season.
- A rear extension is usually survivable if the existing kitchen and a bathroom remain functional and temporary weatherproofing can separate the works. Expect dust everywhere regardless.
- A second-storey addition generally is not. The roof comes off and the house is tarpaulin-protected for weeks — which in a Melbourne winter is genuinely untenable.
- Restumping requires vacating for at least the days the house is lifted.
- Any extension involving the only kitchen or bathroom requires a temporary arrangement or relocation.
Melbourne-specific practicalities:
- Heat the occupied zone. A house with an open wall or a partly removed roof in July is cold in a way that a Brisbane equivalent is not. A portable heater and sealed plastic barriers with zippered access make the difference between manageable and miserable.
- Dust migration is worse in winter, because windows cannot be opened. A negative-pressure fan in the works area is worth the hire cost.
- A temporary kitchen needs warmth as well as water. A garage or laundry with a sink, fridge, microwave and induction plate works; an unheated one in June does not.
- Storage — $200 to $500 per month for a typical household.
- Temporary accommodation — $2,500 to $6,500 per month for a Melbourne family home.
Two weeks of accommodation during the most disruptive phases often costs less than the programme extension caused by working around a household.
Getting the Design Brief Right
The extensions that disappoint are usually the ones where the brief was expressed as area rather than function. Before engaging a designer, write down:
- What specifically does not work in the current house, room by room
- How the household actually uses the space — where people gather, work, and need quiet
- Which rooms are used at which times of day, which determines where the sun should be
- How the house should perform in winter, which in Melbourne is a design requirement rather than a preference
- What storage is missing and where it should be
- Which outdoor space matters and how the house should connect to it
- The budget, honestly, including consultants, permits and contingency
- How long you intend to stay
A designer given this brief will produce a better extension than one asked for “another forty square metres and an open-plan kitchen”.
The Question to Ask Every Builder
Before signing anything, ask each builder how they intend to handle the junction between the new addition and the existing house — specifically, what happens to the connection when the clay swells in winter and shrinks in summer.
A builder who has worked properly in Melbourne will describe an articulation joint, or matched foundation systems, or a recommendation to restump the existing house first. A builder who says the two will simply be tied together has told you their extensions crack, and that yours will too. It is the single most useful question you can ask in this city, and the answer takes thirty seconds.