Extending an existing house is often more cost-effective than selling and upsizing, especially in Melbourne suburbs where stamp duty and agent fees on a $1.8 million purchase can easily exceed $100,000. In 2026, most home extensions Melbourne homeowners commission cost between $2,400 and $6,500 per square metre, with the final figure shaped by scope, storey, site conditions, and finish selections.
This guide gives Melbourne homeowners a full 2026 cost breakdown for single-storey, second-storey, and small home extensions, the hidden expenses most builders skip over, and the permits you need before work begins.
1. Ground Floor (Single-Storey) Extension Cost
A single-storey rear or side addition is the most common type of extension. It usually adds a larger kitchen, family room, or master suite to an existing home.
Typical 2026 ranges:
- Standard specification: $2,400 to $3,200 per square metre
- Mid-range specification: $3,200 to $4,000 per square metre
- Premium or architectural specification: $4,000 to $5,000+ per square metre
A 30 square metre rear extension therefore costs between $72,000 and $150,000 for the build alone, before permits and finishes.
2. Second-Storey Extension Cost
Second-storey additions are significantly more expensive than ground floor work because they require structural re-engineering, internal stair access, and temporary roof removal.
Typical 2026 ranges:
- Standard specification: $4,100 to $5,200 per square metre
- Mid-range: $5,200 to $6,000 per square metre
- Premium: $6,000 to $7,500+ per square metre
A 60 square metre upper level usually lands between $246,000 and $450,000 depending on design, structural reinforcement, and finish selections.
3. Small Home Extension Cost (Under 25 m²)
Small extensions, such as a master suite, walk-in robe, or laundry-bathroom addition, often carry a higher per-square-metre rate because fixed costs (engineering, permits, site set-up) are spread across a smaller floor area.
A small home extension in Melbourne typically costs $80,000 to $140,000 for a 20 to 25 square metre addition with standard finishes. According to the Housing Industry Association, demand for small additions has stayed strong through 2025 as homeowners hold off on selling.
4. Planning and Building Permit Costs
Most extensions in Victoria need at least a building permit, and many also need a planning permit if the property sits on a heritage overlay, changes the building envelope, or alters site coverage. Permit fees usually run $1,500 to $4,500 for a typical extension. Council fees, soil tests, surveys, and engineering reports add another $2,000 to $6,000.
For more on what triggers a planning permit, read the HBK guide on things to consider when remodelling your home.
5. Design and Architect Fees
A draftsperson typically charges between $3,000 and $8,000 for a single-storey extension drawing package. A registered architect typically charges 6 to 12 percent of construction cost for a full-service package that covers design, documentation, and contract administration. On a $200,000 build, that is $12,000 to $24,000.
6. Site Conditions That Add Cost
Three site factors quietly push extension budgets higher:
- Sloping blocks add 8 to 15 percent for retaining walls, stepped footings, or engineered piers
- Restricted access (no truck access, neighbouring fences close) adds 5 to 10 percent for manual material handling
- Heritage overlay can require matching brickwork, timber profiles, or hand-finished joinery that triples the cost of standard items
Mornington Peninsula, parts of Glen Eira, and Bayside frequently involve at least one of these factors.
7. Demolition and Make-Good Costs
Tying new into old almost always means demolishing part of the existing house: removing an external wall, reframing an opening, or temporarily propping a roof. Budget $4,000 to $12,000 for demolition, removal, and structural make-good on a typical single-storey extension. Asbestos disposal, if required, adds $1,500 to $4,000.
8. Finishes Drive Up to Half the Final Price
Two extensions of the same size can finish $100,000 apart based purely on finish selections. Engineered timber floors, full-height tiles, stone benchtops, custom joinery, smart-home cabling, and double-glazed sliding stackers can add $40,000 to $80,000 across a 40 square metre addition. Set your finish budget early and lock it into the contract.
9. Contingency Budget
Always set aside 10 to 15 percent contingency for unexpected issues like asbestos, failed original waterproofing, outdated wiring, termite damage, or unsuitable footings under the existing slab. On a $200,000 build, that is a $20,000 to $30,000 cushion. The Australian Bureau of Statistics reports that the most common cause of overruns on renovation projects is undisclosed pre-existing structural or waterproofing damage.
10. Is a Small Second Dwelling a Cheaper Alternative?
For some homeowners, a detached second dwelling at the rear of the block is cheaper than a full extension. Typical 2026 ranges run $2,200 to $3,400 per square metre for a 40 to 60 square metre unit, often with no internal disruption to the main house. Recent Victorian planning reforms have made many smaller second dwellings exempt from a planning permit provided they meet size and setback rules.
For a side-by-side look at the options, see the HBK page on home extensions Melbourne.
How Long Does an Extension Take to Build?
A typical single-storey extension takes 4 to 6 months from contract signing to handover. Second-storey extensions usually take 6 to 9 months because of the additional structural and weather-protection work involved. Master Builders Victoria reports that construction timeframes have lengthened by an average of 15 percent since 2022 because of trade availability and supply chain conditions.
Frequently Asked Questions
Q. What is the cheapest type of home extension in Melbourne?
A. A single-storey rear extension with a standard specification (timber frame, tiled roof, standard kitchen and bathroom fittings) is usually the most affordable option, starting at around $2,400 per square metre.
Q.Do I need a planning permit for an extension?
A. Many extensions do, especially on heritage overlays, in flood or bushfire zones, or where the work changes the building envelope beyond the VicSmart limits. Always check with your local council before signing a contract.
Q. Is it cheaper to extend up or out?
A. Extending out (ground floor) is usually cheaper per square metre because second-storey extensions require structural reinforcement, internal stair access, and temporary roof works. Building up, however, keeps your backyard intact.
Q. How long does a home extension take to build?
A. Typically 4 to 6 months for a single-storey extension and 6 to 9 months for a second storey, from contract signing through to handover.
Get a Fixed-Price Extension Quote
HBK Constructions has delivered home extensions across Melbourne for 20 years, with completed projects in Bentleigh East, Brighton, Hampton, Mentone, Mornington, Mount Eliza, and Frankston South. Every project is a fixed-price contract with full insurance, milestone-based payments, and a twelve-month defect liability period.
What sets HBK apart:
- VBA-registered Victorian builder
- Fixed-price contracts with no hidden variations
- Domestic Building Insurance included on projects over $16,000
- End-to-end project management with in-house trades
- Local experience across Glen Eira, Bayside, Kingston, Mornington Peninsula, and Frankston
Contact HBK Constructions today for a free site assessment and a fixed-price quote on your extension.
Phone: 0400 200 415
Email: info@hbkconstructions.com.au
Website: hbkconstructions.com.au