Building a Duplex in Sydney: Rules, Costs & What to Know Before You Start
Introduction
Duplex developments have become an increasingly popular option for Sydney homeowners and investors looking to maximise land value without moving into large-scale development.
However, building a duplex involves more than just construction. Planning controls, approvals, site constraints, and cost considerations all play a major role in whether a project is viable and successful.
This guide outlines what to know before building a duplex in Sydney, including rules, costs, and key considerations to help you plan with confidence.
What Is Considered a Duplex in NSW?
In NSW, a duplex is classified as a multi-dwelling housing development, typically consisting of two attached dwellings on a single lot.
Duplexes can be:
Torrens titled
Strata titled
The classification affects approvals, services, and long-term ownership structure.
Duplex Planning Rules in Sydney
Duplex developments in Sydney may be approved under:
Local Council Development Applications (DA), or
NSW Complying Development (CDC) pathways
Key factors that influence approval include:
Zoning
Minimum lot size and frontage
Building height and setbacks
Floor space ratio (FSR)
Private open space requirements
Each council applies controls differently, so early planning advice is essential.
Can My Site Support a Duplex?
Not every block is suitable for a duplex. Key considerations include:
Land size and frontage
Site slope and orientation
Easements and services
Bushfire, flood, or heritage constraints
Vehicle access and parking requirements
A feasibility assessment early on can help avoid costly design work on unsuitable sites.
How Much Does It Cost to Build a Duplex in Sydney?
As a general guide, duplex construction costs in Sydney typically start from around $1.2m and can exceed $2m+, depending on design, site conditions, and finish level.
Cost factors include:
Structural complexity
Shared walls and fire separation
Services and infrastructure upgrades
Driveways, landscaping, and fencing
Approval and consultant fees
A clear scope and early cost alignment are critical to maintaining feasibility.
Design Considerations That Affect Value
Good duplex design balances build efficiency with long-term value.
Key design considerations include:
Functional layouts for both dwellings
Natural light and ventilation
Acoustic separation
Street presence and resale appeal
Consistent quality across both homes
Cutting corners in design often impacts resale value and buyer appeal.
Design & Construct vs Traditional Tendering for Duplexes
Duplex projects involve more complexity than single dwellings, making early coordination critical.
A design & construct approach allows:
Budget input during design
Better control over construction methodology
Reduced redesign after pricing
Streamlined communication
This can help maintain feasibility and reduce delays, particularly on tight sites.
Common Mistakes to Avoid
Some common pitfalls include:
Underestimating approval timeframes
Designing before confirming site suitability
Over-spending on finishes that don’t improve value
Engaging builders too late in the process
Early planning and professional guidance help avoid these issues.
Final Thoughts
Building a duplex in Sydney can be a smart way to maximise land value, but success depends on careful planning, realistic budgeting, and the right delivery method.
Understanding the rules, costs, and process before you start helps ensure your project is viable and delivered efficiently.
Frequently Asked Questions
What zoning is required to build a duplex in Sydney?
Duplex developments are generally permitted in specific residential zones, subject to local council controls or NSW Complying Development rules. Zoning and minimum lot requirements vary by area.
How long does it take to build a duplex?
Once approvals are in place, duplex construction typically takes between 10–14 months, depending on design complexity, site conditions, and weather.
Is a duplex a good investment in Sydney?
A well-designed duplex can offer strong long-term value, particularly in high-demand areas. Success depends on site suitability, construction quality, and planning controls.
Can one side of a duplex be sold separately?
Yes. Duplexes can be subdivided under Torrens or strata title, subject to approvals and servicing requirements.
If you’re considering a duplex or multi-dwelling project and want clarity on feasibility, costs, and approvals, speak with a builder experienced in managing complex residential builds.
Contact CETA Projects to discuss your duplex project and next steps.
