Building a duplex in Australia can run from about $550,000 to $1.3 million. Wollongong comes with its own cost quirks. After 25 years of building duplexes across the South Coast, I’ve seen one pattern repeat: most people underestimate the real price.

Important Disclaimer:
“This article is general guidance, not an exact price guide, guaranteed returns, or a substitute for professional advice or a formal quote. Construction costs, rental yields, and capital growth examples reflect 2025 conditions and will vary with site constraints, design, materials, and market movements. Speak with a qualified financial adviser before making investment decisions. For accurate estimates and design recommendations for your site, contact CKS Projects. We’ll provide a comprehensive consultation and a formal quote tailored to your Wollongong duplex. “

The builder’s quote is not your final spend

Professional fees, site works, council charges, landscaping, and similar items typically add 25 to 35 percent to the base construction price. At CKS Projects, we walk clients through the complete budget up front, so there are no unpleasant surprises once construction starts.

Understanding Total Duplex Construction Costs

Duplex cost in Wollongong depends on factors most first-timers don't consider. Let me break down what you're actually paying for.

Base Construction Costs for Wollongong Duplexes

Expect to pay between $400,000 and $700,000 per unit for construction alone. That's $800,000-1.4 million total for both dwellings before any additional expenses.

Wollongong's construction costs sit slightly below Sydney but above regional NSW. Sydney duplex construction ranges from $600,000 to $1.2 million, while Wollongong typically runs $700,000-1.1 million for comparable quality.

Per square metre pricing helps compare options accurately. In 2025, duplex construction costs typically range from $2,000 to $3,800 per square metre. Standard Wollongong duplexes average $2,400-2,800 per square metre for quality finishes.

A 150sqm dwelling costs $360,000-420,000 to construct. Multiply by two dwellings, you're at $720,000-840,000 base construction. That's before site works, professional fees, or landscaping.

Hidden Costs That Blow Your Budget

Council contributions, soil tests, utility connections, and landscaping can add 15-20% to your base cost. Most builders' quotes exclude these expenses entirely.

Wollongong Council charges section 7.11 and 7.12 contributions ranging $15,000-35,000 per duplex depending on location. Water and sewer connection fees add another $10,000-15,000 per dwelling. That's $50,000-100,000 in council costs before you've poured concrete.

Geotechnical reports cost $1,500-2,500 but prevent $50,000+ foundation disasters. Wollongong's varied geology, from coastal sand to escarpment rock, means this report isn't optional, it's essential insurance.

Landscaping, driveways, fencing, these "finishing touches" cost $40,000-70,000 for both dwellings. Quality paving, established gardens, and automatic irrigation all add up faster than you'd believe.

Regional Cost Variations Across the South Coast

coastal view in Australia — Not all **Wollongong** suburbs cost equally to **build** in. Northern suburbs like Thirroul and Austinmer command premium pricing for everything, from land to trades.
Coastal suburbs with difficult access increase costs 10-15%. Narrow streets, limited parking for tradies, material delivery challenges, these logistics add genuine expenses. Central **Wollongong** and suburbs with easy access cost less.
Southern suburbs like Albion Park and Shellharbour offer more affordable **duplex** construction. Land costs less, trades charge standard rates, and council fees sit lower. Your $1.1 million **Wollongong** duplex might cost $950,000 in Shellharbour.

Breaking Down the Major Cost Components

Understanding where money goes helps you make informed decisions about what's worth spending on.

Site Preparation and Earthworks

Site preparation on sloped blocks can add another $50,000-$100,000 to construction costs. Wollongong's hilly terrain makes this particularly relevant.

Flat blocks need minimal site works, $10,000-20,000 for basic leveling and services trenching. Moderately sloped sites require cut and fill, retaining walls, specialised drainage. Budget $40,000-70,000 for these extras.

Severely sloped blocks, common in western Wollongong suburbs and escarpment areas, need extensive earthworks, multiple retaining walls, and complex drainage systems. These sites can add $80,000-120,000 to base construction costs.

Rock excavation presents expensive challenges. Hitting rock during excavation costs $150-250 per cubic metre to remove. Severe rock conditions add $30,000-60,000 to project budgets.

Materials and Labour Expenses

About a quarter to a third of construction costs go to paying workers. Wollongong labour rates sit below Sydney but exceed rural NSW significantly.

Skilled trades, plumbers, electricians, carpenters, charge $80-120 per hour. Your duplex needs hundreds of trade hours across multiple disciplines. Labour alone consumes $200,000-350,000 of total construction budget.

Material costs fluctuate with market conditions. Timber, steel, and concrete all vary based on supply and demand. Materials for duplex construction include lumber, concrete, roofing, windows, doors, plumbing, electrical wiring, and HVAC systems.

Quality specifications dramatically affect material costs. Budget kitchen and bathroom fixtures save $15,000-20,000 per dwelling but look cheap and need replacement sooner. Premium fixtures add $25,000-35,000 per dwelling but last decades and attract better tenants.

Professional Fees You Can't Avoid

Architects usually charge 5% to 12% of the building cost, and builders take another 10% to 20% for project management. These fees aren't negotiable for quality duplex projects.

Architectural design for Wollongong duplexes costs $15,000-35,000, depending on customisation. Off-the-shelf designs cost less but might not suit your block. Custom designs cost more but maximise your site's potential.

Structural engineering fees run $8,000-15,000. Civil engineering for drainage and services adds $5,000-10,000. Building certification costs $5,000-8,000. Survey work needs another $3,000-6,000.

Your total professional fees reach $40,000-75,000 easily. Professional fees including architects, engineers, and certifiers typically add 8-12% to your construction budget.

Factors That Increase or Decrease Your Duplex Costs

Smart decisions during planning dramatically affect final costs. Here's where money gets saved or wasted.

Block Conditions and Topography

The condition of your building site can impact construction costs, with accessibility, soil quality, and terrain all affecting foundation and site preparation requirements. Wollongong blocks vary enormously.

Coastal blocks with high water tables need specialised drainage and damp-proofing. Budget extra $15,000-25,000 for these protections. Escarpment blocks with reactive clay soils need deeper foundations costing $20,000-40,000 more than standard slabs.

Access affects costs significantly. Blocks with good street access for concrete trucks, material deliveries, and waste removal cost less. Difficult access sites add 5-10% to labour costs as everything takes longer.

Design Complexity and Finish Quality

Simple rectangular duplex designs with standard finishes cost the least. Complex shapes, multiple roof lines, extensive glazing, these architectural features add 15-25% to construction costs.

Single-storey duplexes cost $2,200-2,600 per square metre. Two-storey duplex construction typically exceeds $650,000 total and averages $2,600-3,200 per square metre due to structural complexity and additional trade coordination.

Finish quality presents clear cost tiers. Basic spec (laminate benchtops, carpet, standard fixtures) costs $2,000-2,400 per sqm. Mid-range spec (stone benchtops, hybrid floors, quality fixtures) runs $2,400-2,800 per sqm. Premium spec (high-end everything) exceeds $3,000 per sqm easily.

CKS Projects typically recommends mid-range specifications. They deliver quality that justifies rental premiums without overcapitalising on features tenants won't pay extra for.

Council Requirements and Approval Pathways

Wollongong Council requirements significantly impact project costs and timelines. Understanding approval pathways prevents expensive delays.

Complying Development Certificate (CDC) projects cost less in approval fees ($3,000-5,000) and complete faster. Development Application (DA) projects need $8,000-15,000 in fees and take 12-16 weeks minimum.

Meeting building codes and obtaining permits are important but come with fees. Construction certificates cost $3,000-5,000 additional. Occupation certificates add another $1,500-2,500.

Sites requiring DA due to slope, vegetation, or non-standard designs face higher consultant fees. Additional reports, traffic studies, acoustic assessments, arborist reports, these add $5,000-15,000 to project costs.

Making Your Duplex Project Financially Viable

Successful duplex projects require realistic budgeting and smart cost management throughout construction.

Realistic Budget Planning With Contingencies

Your all-in budget should include a 10-15% contingency fund on top of the final estimate. Every duplex project encounters unexpected costs.

Start with land cost. Wollongong duplex-suitable blocks cost $600,000-900,000 depending on location and size. Add $800,000-1.1 million construction. Include $100,000-150,000 for all additional costs. You're at $1.5-2.15 million total project cost.

Contingency funds cover variations, unforeseen site conditions, and market price fluctuations. Without contingency, minor issues derail projects or force quality compromises. Budget 10% minimum, 15% safer.

Finance structuring matters enormously. Banks typically lend up to 80% of the project's end value for construction loans. You need 20% plus costs as cash or equity.

Cost-Saving Strategies That Don't Compromise Quality

Smart savings come from efficiency, not cutting corners. CKS Projects knows where money saves without sacrificing outcomes.

Off-peak construction timing saves 5-10% on trade costs. Starting projects in March-October when demand drops means better trade availability and more competitive pricing.

Standard designs modified for your block cost less than full custom architecture. You're saving $10,000-20,000 in design fees while still getting appropriate solutions.

Material selection offers savings without quality compromise. Choosing locally available bricks over imported stone saves substantially. Using porcelain tiles that look like marble costs half as much and performs identically.

Avoid unnecessary design complexity. Every corner, roof valley, and level change adds cost. Simpler forms built well outperform complex designs built cheaply.

Expected Returns on Your Investment

A profitable duplex project typically targets a Gross Rental Yield of 5%+ and a Development Margin of 20%+. Wollongong market conditions support these returns with proper planning.

Your $1.7 million duplex (land plus construction plus costs) should rent for $1,200-1,400 weekly combined. That's $62,400-72,800 annual income, delivering 3.7-4.3% gross yield. After costs, the net yield sits around 2.5-3.2%.

Capital growth matters more long-term. Wollongong property appreciates 4-6% annually on average. Your $1.7 million investment grows $68,000-102,000 yearly through appreciation.

Development margin (profit if selling immediately) requires end value exceeding total costs by 20%+. Your $1.7 million duplex should appraise at $2.04 million+ to justify the project financially.

CKS Projects provides transparent, detailed cost breakdowns for every Wollongong duplex project. Our years of experience means we accurately estimate all expenses upfront, from base construction through council fees to landscaping. We help clients understand true project costs and make informed decisions about design, finishes, and timing that deliver strong returns without budget blowouts.

Ready for an honest conversation about what your duplex will actually cost? Let's discuss your specific site and create a comprehensive budget.

About the Author

Keiron Moore is the Director of CKS Projects with over 25 years of experience building duplexes across Wollongong and the South Coast. He provides transparent cost guidance and detailed budget planning, helping clients understand true duplex construction expenses and make informed decisions that deliver strong returns without financial surprises.