How Much Does a Double Storey Extension Cost?

A double storey extension price in Melbourne typically ranges from $3,000 to $5,000 per square metre, but the final cost depends on several factors specific to your property and vision.

At Cameron Construction, we’ve helped hundreds of Melbourne homeowners understand where their budget goes and how to make informed decisions about their investment.

Where Your Double Storey Extension Budget Actually Goes

Foundation and Structural Work

Foundation and structural work typically accounts for 15–20% of your total project cost, making it one of the largest individual expenses. This phase includes site preparation, soil reports, footing design, and the concrete slab or stumps that support your new structure. Melbourne’s variable soil conditions mean soil reports are essential-they cost approximately $20 for up to five samples but prevent costly surprises later.

The building surveyor and structural engineer use soil data to design appropriate foundations, and skipping this step often leads to expensive remedial work. If your block has poor soil, steep slopes, or limited access, foundation costs can climb significantly, sometimes reaching 25% of the total budget.

Materials and Labour Costs

Materials and labour represent the bulk of your extension cost, splitting roughly 50–65% of the budget between them. According to Rawlinson’s Construction Cost Guide, a double storey extension in Melbourne costs around $2,570 per square metre for basic services and $3,256 per square metre for fully serviced finishes, with high-quality finishes reaching $4,560 per square metre.

Labour costs in Victoria remain competitive compared to other states, but skilled trades-framers, electricians, plumbers, and plasterers-command premium rates for quality work. Material prices fluctuate with market conditions; timber, steel, and concrete have all seen price volatility over recent years, so locking in quotes early protects against cost escalation.

Design and Engineering Fees

Design and engineering fees typically run 5–8% of the project cost, covering architectural drawings, structural plans, and BCA compliance documentation. Councils require these before issuing a building permit, and quality designs prevent costly construction errors and delays.

Many homeowners underestimate this cost, expecting permits to be free or cheap, but a comprehensive engineering package for a double storey addition costs $4,000 to $8,000 depending on complexity and your block’s characteristics. Understanding these three cost pillars positions you well to evaluate quotes and identify where builders allocate your budget-which brings us to the factors that actually shift these numbers up or down for your specific property.

Factors That Influence Double Storey Extension Pricing

Block Size and Site Complexity

Your Melbourne block’s characteristics shift costs far more than general pricing guides suggest. A 50-square-metre extension on flat land with straightforward soil costs substantially less than an identical footprint on a sloping block with poor drainage or heritage overlays. Soil reports from your engineer reveal whether you need deep footings, pilings, or reinforced slabs-costs that vary depending on what lies underground.

A block requiring minimal site work uses a standard concrete slab at $150–$200 per square metre, while poor soil or steep grades push foundation costs to $400–$600 per square metre. Melbourne’s variable geology means two adjacent properties can have vastly different foundation expenses, so soil testing early prevents budget shocks mid-project.

Local Council Requirements and Planning Permits

Council requirements compound these variations significantly. Planning permits add $2,000 to $8,000 in fees and design time, particularly if your extension affects setbacks, overshadows neighbours, or sits in a heritage area. Building permit levies in Victoria depend on your estimated cost of works and municipality-the Victorian Building Authority’s Building Permit Levy Calculator shows levies ranging from $500 to $3,500 for typical extensions.

Some councils demand traffic impact reports, arborist assessments, or structural certification that others don’t, so your specific location determines hidden costs. Your local council’s planning department can clarify which requirements apply to your property before you commit to a design.

Quality of Finishes and Specifications

Finishes quality amplifies labour and material expenses dramatically. Basic finishes cost around $2,085 per square metre, while high-quality finishes reach $4,560 per square metre according to Rawlinson’s Construction Cost Guide-that’s more than double the price for the same structural shell. Specifying materials, appliances, and colour schemes upfront prevents provisional cost items that builders use to cover unknowns, which inevitably blow out during construction.

Vague specifications like prime cost sums or provisional sums shift risk to you and guarantee cost surprises. Lock your finishes in writing before construction starts, and avoid allowing the builder discretion on materials or fittings. Once you understand how these factors shape your budget, managing costs becomes a matter of making informed decisions at each stage-starting with how you source and evaluate builder quotes.

Ways to Manage Your Double Storey Extension Budget

Get Multiple Quotes from Qualified Builders

Three written quotes from registered builders form the foundation of smart budget management, and they must cover identical plans and specifications. Consumer Affairs Victoria states that obtaining at least three quotes on the same scope prevents price manipulation and reveals genuine market rates for your project. When you compare quotes, check what each one includes: some builders price finishes separately, others bundle them, and some exclude permit costs or site preparation. A $500,000 quote might exclude $15,000 in council fees, structural engineering, or soil testing, so line-by-line comparison matters more than the headline number.

Verify every builder holds current domestic building insurance before they start work-Victorian law requires this for projects exceeding $16,000. Check their registration on the Building and Plumbing Commission website and review their disciplinary history on ASIC. Unregistered or uninsured builders expose you to massive liability if something goes wrong.

Plan for Contingency Costs

Contingency costs should sit at 10–15% of your total budget, not the 5% many homeowners assume. This covers the soil issues that soil reports didn’t fully reveal, the structural surprises that emerge once walls come down, and the material price spikes that occur mid-project. A $500,000 extension with only 5% contingency ($25,000) leaves you dangerously exposed when your electrician finds outdated wiring requiring expensive upgrades or your concrete slab needs reinforcement.

Understand Payment Schedules and Milestones

Payment schedules must follow stages: deposit at signing, then payments at base, frame, lock-up, and fixing stages-never pay in full upfront or large lump sums before work is complete. Consumer Affairs Victoria recommends paying only after you inspect and approve each stage. Write all variations to the contract in writing before work proceeds; verbal agreements about changes guarantee cost blowouts because disputes arise over what was actually agreed.

Lock Finishes and Specifications in Writing

Specifications that remain vague create provisional cost items that builders use to cover unknowns, which inevitably blow out during construction. Lock your finishes in writing before construction starts, and avoid allowing the builder discretion on materials or fittings. Once your budget locks finishes, specifications, and payment milestones in writing, you eliminate most budget surprises and position yourself to complete the project without financial stress.

Final Thoughts

A double storey extension price in Melbourne reflects foundation complexity, material quality, council requirements, and labour rates specific to your property. The factors we’ve covered-soil conditions, planning permits, finish specifications, and payment schedules-determine whether your project lands at $3,000 or $5,000 per square metre. Understanding these variables prevents budget surprises and positions you to make decisions that protect your investment.

Double storey extensions typically add 10–15% to your property’s value, though this varies by location, quality, and market conditions. A well-executed extension that improves functionality and meets current building standards attracts buyers and justifies the cost. The key is locking specifications, obtaining multiple quotes from registered builders, and planning contingency costs before construction begins.

Getting your extension quote starts with three steps: engage a registered building surveyor or town planner to clarify whether planning and building permits apply to your property, commission a soil report if your block shows any complexity, and brief three qualified builders on identical plans and specifications so you can compare genuine market rates. We at Cameron Construction have guided hundreds of Melbourne homeowners through this process, and our in-house designers, engineers, and project managers handle everything from concept through completion, including planning, permits, and BCA compliance across Melbourne’s councils. Contact us to discuss your project and receive a detailed quote tailored to your property’s specific needs.