How Much Does a Home Extension Cost?

Planning a home extension in Melbourne requires careful budgeting and realistic cost expectations. The question “how much does a home extension cost” depends on multiple factors that can significantly impact your final investment.

At Cameron Construction, we’ve guided hundreds of Melbourne homeowners through extension projects ranging from $50,000 ground floor additions to $200,000+ double storey builds. Understanding these cost variables helps you make informed decisions about your home’s future.

Factors That Affect Home Extension Costs

Extension costs in Melbourne vary dramatically based on five primary factors that determine your final investment. The size of your extension represents the most significant cost driver, with ground floor additions averaging $2,500-$4,000 per square metre and double storey builds reaching $3,500-$5,500 per square metre according to recent construction data. A 40-square-metre ground floor addition typically costs $100,000-$160,000, while the same space as a double storey addition ranges from $140,000-$220,000 due to structural complexity and advanced structural requirements.

Material Selection Impact

Premium materials can double your extension costs compared to standard specifications. Engineered stone benchtops add $800-$1,200 per linear metre versus $300-$500 for laminate options. Hardwood floors cost $180-$300 per square metre compared to $60-$120 for hybrid alternatives. We recommend you allocate 30-40% of your budget to materials and finishes, with kitchen and bathroom spaces that require the highest investment per square metre.

Site Conditions and Access Challenges

Sloping blocks increase foundation costs by 25-50% due to additional excavation and retaining requirements. Sites with limited access for machinery add $15,000-$30,000 to project costs through manual handling and crane requirements. Clay soil conditions (common across Melbourne’s eastern suburbs) require deeper footings, which adds $8,000-$15,000 to structural costs.

Council Requirements and Permit Costs

Council permit fees range from $1,453 for projects under $500,000 to over $28,000 for extensions exceeding $15 million in development value. Planning applications start at $220 for minor works but can reach $1,420 for developments between $100,000-$500,000. These regulatory costs represent just the beginning of your extension journey, as the actual construction phase brings its own set of financial considerations that Melbourne homeowners must understand.

Average Extension Costs in Melbourne

Melbourne extension costs vary significantly across project types, with ground floor additions starting at $100,000 for basic 40-square-metre builds and premium double storey extensions reaching $350,000+ for complex designs. Single storey extensions average $2,500-$4,000 per square metre, making a standard 50-square-metre addition cost $125,000-$200,000 based on finishes and site conditions. Double storey builds command $3,500-$5,500 per square metre due to structural requirements, with 80-square-metre projects costing $280,000-$440,000 according to Australian Bureau of Statistics construction data from 2023-24.

Ground Floor Extension Costs

Ground floor additions deliver the most cost-effective space solution for Melbourne families. A 40-square-metre ground floor extension costs $100,000-$160,000 with standard finishes, while premium specifications push costs to $180,000-$220,000. These projects require minimal structural work compared to double storey builds, which keeps foundation costs at $15,000-$25,000 for most sites.

Clay soil conditions (common in eastern Melbourne suburbs) add $8,000-$15,000 to foundation requirements through deeper footing specifications.

Double Storey Addition Costs

Double storey extensions provide maximum space efficiency on smaller blocks but require substantial structural investment. A typical 80-square-metre double storey addition costs $280,000-$440,000, with structural engineering fees alone reaching $8,000-$15,000. These builds add 40-60% more floor area than single storey options while increasing property values by $30,000-$50,000 beyond construction costs. Second storey conversions cost 20-30% less than new double storey builds but need existing roof removal and structural upgrades.

Kitchen and Bathroom Extension Costs

Kitchen extensions represent the highest cost per square metre at $4,500-$7,500 due to plumbing, electrical, and appliance requirements. A 25-square-metre kitchen extension with premium finishes costs $112,500-$187,500, while bathroom additions range from $35,000-$65,000 for 15-square-metre spaces. Combined kitchen-bathroom extensions in double storey builds reduce per-square-metre costs by 15-20% through shared plumbing and structural work.

Smart budget allocation becomes critical once you understand these baseline costs, as strategic decisions about where to invest and where to save can significantly impact your project’s final value.

Ways to Manage Your Extension Budget

Successful extension budgets require a 20-25% contingency above your base construction estimate, as Melbourne projects consistently exceed initial projections due to unforeseen site conditions and material price fluctuations. Allocate your budget with 60% for construction, 15% for materials upgrades, 10% for permits and professional fees, and 15% for contingencies.

The Australian Bureau of Statistics reports that building construction prices have risen due to increased labour costs and material price pressures, which makes realistic budgets more critical than ever for extension success.

Strategic Spending Priorities

Focus your premium budget allocation on structural elements and waterproofing that cannot be easily upgraded later, while you save on cosmetic finishes that can be improved over time. Spend 40% of your materials budget on foundations, framing, and roof work, as these elements determine long-term performance and cannot be economically modified after completion. Kitchen and bathroom spaces justify premium investment at $4,500-$7,500 per square metre because they deliver the highest return on investment and daily functionality improvements.

Save money on flooring, paint colours, and light fixtures that can be upgraded affordably in future years without structural disruption. These cosmetic elements offer flexibility for budget-conscious homeowners who want to spread costs over multiple years.

Avoiding Cost Blowouts

Experienced extension builders reduce cost overruns by 30-40% compared to general contractors unfamiliar with Melbourne’s council requirements and site challenges. Builders with established supplier relationships secure materials at 15-20% below retail prices and avoid the delivery delays that add $200-$400 per day in project extensions.

Fixed-price contracts with detailed specifications prevent scope creep that typically adds 10-15% to project costs. Stage payments tied to completion milestones protect your budget from builder cash flow issues that can derail timelines and increase expenses.

Planning for Unexpected Costs

Melbourne’s clay soil conditions (common across eastern suburbs) can add $8,000-$15,000 to foundation requirements through deeper footings. Sites with limited access for machinery increase costs by $15,000-$30,000 through manual handling and crane requirements. Weather delays during winter months can extend project timelines by 2-4 weeks, which adds holding costs for temporary accommodation or storage.

Set aside 5-10% of your total budget as a contingency fund for these unexpected expenses. Consider implementing a phased approach to spread costs over time if budget constraints are a concern.

Final Thoughts

Melbourne home extension costs range from $100,000 for basic ground floor additions to $440,000+ for premium double storey builds, with the answer to “how much does home extension cost” depending on size, materials, site conditions, and council requirements. Professional planning prevents the 10-15% cost overruns that plague poorly managed projects. Experienced builders reduce expenses through established supplier relationships and detailed specifications.

Realistic budgets with 20-25% contingencies protect against Melbourne’s unpredictable clay soil conditions and access challenges (which can add $15,000-$30,000 to project costs). Strategic material selection and phased construction approaches help homeowners manage cash flow while they achieve their space and functionality goals. Smart budget allocation focuses premium investment on structural elements that cannot be easily upgraded later.

We at Cameron Construction have delivered extensions across Melbourne for over four decades, handling concept to completion including planning, permits, and council compliance. Our in-house team eliminates the coordination issues that typically increase costs and extend timelines for extension projects. Contact us today to discuss your extension plans and receive a detailed cost estimate for your Melbourne home.