Render of a modern two storey duplex with timber entry doors and landscaped front gardens

Duplex Builders Sydney

A duplex turns one block into two homes, for family, rental yield or resale. We design and build dual occupancies across Sydney under one design and construct contract, from the first feasibility check to the keys for both dwellings.

Discuss your project

Licensed builder
NSW Class 2 Building Practitioner
14+ years building in Sydney
5.0 on Google

Dual occupancy, designed and built by one team

Most duplex budgets go wrong before construction starts. A design is drawn without a builder’s input, the approval pathway is guessed, and the price comes back well above the numbers the project was bought on. Design and construct closes that gap: we test the site, the controls and the cost first, then design two homes that build cleanly and sell or rent well.

You get one point of accountability for design, approvals and construction, and a programme you can plan finance and rent around.

The approval pathway

The NSW low and mid-rise housing reforms, in force since July 2024, made dual occupancies permissible with consent in most R2 low density zones. That opened up a lot of Sydney blocks, but your council’s lot size and frontage controls still apply, and the complying development pathway has changed several times since.

So we start every duplex with the controls for your lot: zoning, minimum lot size, frontage, heritage, flood and bushfire overlays, and whether a CDC is available or a DA is needed. The pathway sets the timeline as much as the design does.

Side by side or one above the other

A side by side duplex is usually Class 1a under the Building Code of Australia. Stack one dwelling above the other and it becomes a Class 2 building, which brings in the Design and Building Practitioners Act: declared designs and a registered building practitioner to build and declare the work.

Shafbuild holds a NSW Class 2 Building Practitioner registration, so either layout is open to you.

Separation done properly

The wall between two dwellings has to meet fire resistance and sound insulation requirements, and services, roof and stormwater need to be split cleanly, especially if you plan to subdivide. We resolve these details in design so they are priced and approved, not argued about on site.

How a duplex project runs

Feasibility
Zoning, lot size and frontage controls, the likely approval pathway, build cost and what the finished dwellings are worth, tested before you spend on design.
Design
Two homes planned together: layouts, the separating wall, services, parking and private open space, priced as the design develops.
Approvals
A complying development certificate where your lot and design qualify, or a development application through council. Subdivision is planned at the same time if you want to sell or finance separately.
Construction
One builder, one contract and one programme for both dwellings, with regular updates and a single point of contact.
Handover
Certification, occupation certificates, warranties and documentation for each dwelling.

Duplex questions

How much does it cost to build a duplex in Sydney?

The main drivers are the site (slope, soil, rock, drainage and access), demolition of any existing house, the size and finish level of the two dwellings, and the approval pathway. We price from a defined scope at feasibility, so you can test the numbers against what the finished dwellings are worth before committing to design.

Can my block take a duplex?

Since July 2024 the NSW low and mid-rise housing reforms have made dual occupancies permissible with consent in most R2 low density zones. Your council still sets lot size and frontage controls, and heritage, flood and bushfire constraints apply. We check all of this for your lot at feasibility.

Can a duplex be approved as a CDC?

Sometimes. The complying development pathway for dual occupancies depends on your council’s controls and the state codes, and the rules have changed several times since 2024. Where your lot qualifies, a CDC is usually faster than a DA. We confirm the current position for your site before design begins.

Can I subdivide and sell one side?

Often, yes, through Torrens or strata subdivision, depending on council controls. Plan subdivision with the design so the separating wall, services and boundaries suit it from the start.

Is a duplex a Class 2 building?

A side by side duplex is usually Class 1a. If one dwelling sits above the other, the building is Class 2 and the work falls under the Design and Building Practitioners Act. Shafbuild is a registered Class 2 building practitioner, so we can build either.