How to Build a Home Extension

Home extensions offer Melbourne homeowners the perfect solution to growing space needs without relocating. Whether you’re planning a double storey addition or expanding your ground floor, understanding the process is essential.

At Cameron Construction, we’ve guided countless families through successful extension projects. Learning how to build a home extension properly saves time, money, and stress throughout your renovation journey.

What Should You Plan Before Starting Your Extension

Define Your Space Needs and Project Scope

Start with precise measurements of your current home and identify exactly which rooms require expansion or addition. Melbourne families typically add 40-80 square metres for double storey extensions, while ground floor additions average 30-60 square metres. Document your family’s daily routines to determine whether you need additional bedrooms, living areas, or kitchen space. Consider future needs over the next 10-15 years, as most Melbourne homeowners stay in extended properties for at least a decade after completion.

Establish Your Budget with Professional Estimates

Extension costs in Melbourne range from $3,500-$5,500 per square metre for quality construction, with double storey additions typically requiring 15-20% more budget than single level builds. Obtain detailed quotes from three registered builders to understand true project costs. Add 15-20% contingency for unexpected issues like poor soil conditions or heritage requirements (particularly common in inner Melbourne suburbs). Factor in temporary accommodation costs if your extension affects kitchen or bathroom access during construction.

Navigate Council Requirements Early

Planning permits are mandatory for most Melbourne extensions, with processing times averaging 8-12 weeks across metropolitan councils. Submit applications before you engage builders, as permit conditions often affect design specifications and construction methods. Heritage overlay properties require additional documentation and may face height restrictions or material requirements. Contact your local council planning department within the first month of project consideration to understand specific requirements for your suburb and property type.

Understand Building Code Compliance

The Building Code of Australia sets strict standards for structural integrity, energy efficiency, and safety requirements that your extension must meet. Extensions over 10 square metres require building permits and registered building surveyor oversight throughout construction. Fire safety regulations become more complex for double storey additions (requiring additional egress windows and smoke detection systems). Your builder must demonstrate compliance with current accessibility standards, particularly for bathroom and kitchen extensions.

Once you complete this planning phase, the next step involves assembling your professional team and finalising your extension design.

How Do You Execute Your Extension Build

Select the Right Professional Team

Your extension project needs three key professionals: a building designer, structural engineer, and registered builder. Melbourne’s Building and Plumbing Commission requires builders to hold current registration for domestic building work, with domestic building insurance mandatory for contracts over $16,000. Interview at least three builders who specialise in your extension type, as double storey specialists understand complex foundation requirements while single level experts excel in seamless integration with existing structures. Verify each builder’s registration number through the VBA website and request references from projects completed within the past 18 months. Architects charge 8-12% of total project costs but add significant value for complex heritage or sloped block sites common across Melbourne’s inner suburbs.

Address Engineering and Structural Requirements

Structural engineers must assess your existing foundation capacity before any extension work begins, particularly for double storey additions which typically require reinforced footings and additional load-bearing elements. Melbourne’s clay soil conditions demand specific foundation designs, with most extensions requiring concrete piers that extend 2-3 metres below ground level. Your engineer will specify steel beam sizes, concrete specifications, and connection details that your builder must follow exactly. Building surveyors conduct mandatory inspections at four stages: foundation, frame, lock-up, and final completion (with each stage requiring approval before work continues).

Manage Construction and Quality Control

Extension projects in Melbourne average 12-16 weeks for single storey additions and 18-24 weeks for double storey builds, depending on complexity and weather conditions. Weekly site meetings with your builder prevent delays and address issues before they become costly problems. Payment should align with completion milestones rather than time periods, with typical stages being foundation (20%), frame (25%), lock-up (25%), fixing (20%), and final completion (10%).

Document progress with photographs and maintain written records of any variations or changes to original specifications.

Your construction team handles the build phase, but legal compliance and insurance requirements demand equal attention throughout your project.

What Legal Requirements Must You Meet

Building Permits and Surveyor Oversight

Building permits are mandatory for most Melbourne extensions, with specific exemptions outlined in Victorian Building Authority guidance. Applications require detailed architectural plans, engineering specifications, and soil reports. The Victorian Building Authority mandates that registered building surveyors conduct inspections at four critical stages: foundation excavation, structural frame completion, lock-up stage, and final completion.

Each inspection costs $400-800 but prevents costly rectification work later. Your building surveyor must approve each stage before construction continues (with penalties up to $33,000 for proceeding without proper approvals). Independent building surveyors offer better oversight than council-appointed alternatives, as they focus solely on code compliance rather than administrative processing.

Domestic Building Insurance Requirements

Domestic building insurance protects homeowners against builder default or death. Coverage is mandatory for all contracts that exceed $16,000 in Victoria. Your builder must provide this certificate before accepting any deposit payments, with policies typically costing 0.5-1% of total contract value.

The insurance covers incomplete work, defective construction, and non-compliance with building standards. Policies remain valid for six years after completion and transfer to new owners if you sell the property. Builders who fail to provide valid insurance face registration suspension and cannot legally commence work on your extension.

Home Insurance and Coverage Updates

Home and contents insurance requires notification before extension work begins. Standard policies exclude coverage during major structural alterations. Most insurers demand professional builder certification and valid building permits before they extend coverage to new areas.

Contact your insurer at least four weeks before construction starts to arrange temporary coverage adjustments. Some insurers charge additional premiums during construction phases (typically 10-15% of annual premium). Document all communications with your insurer and obtain written confirmation of coverage changes.

Statutory Warranties and Defect Protection

Builders must provide statutory warranties that cover structural defects for six years and non-structural issues for two years under Victorian legislation. These warranties are automatic and cannot be excluded from your building contract. Structural defects include foundation problems, load-bearing wall issues, and roof structural failures.

Document all warranty conditions in writing and retain certificates for the full warranty period. Warranty claims average $15,000-25,000 for major extension defects according to Victorian Building Authority data. Report defects immediately in writing to preserve your warranty rights and maintain detailed photographic records of any issues.

Final Thoughts

Home extension projects demand careful coordination between multiple professionals and strict adherence to Melbourne’s regulations. Success depends on early council engagement, accurate cost estimates, and selection of registered builders who understand local requirements. Professional teams prevent costly mistakes and navigate complex compliance standards that protect your investment.

Registered builders, structural engineers, and building surveyors bring essential expertise to your extension project. These professionals handle permit applications, code compliance, and quality control throughout construction. Their knowledge of Melbourne’s soil conditions and heritage requirements (particularly in inner suburbs) saves time and prevents expensive rectification work.

We at Cameron Construction help Melbourne families transform their homes through quality extensions. Our team manages the complete process from initial design through final completion. Contact us to discuss how to build a home extension that meets your family’s needs and budget.