How long does it take to build a duplex?

How long the build itself takes

On our duplex projects, about 12 months is a typical construction period for the two homes, built together under one program. A basement generally adds three to four months, since excavation and the structure below ground come before the homes above can rise.

The build follows the same order as any house we construct, described on our process page. Excavation, footings, slab and frame come first. The roof, windows, cladding and external doors then close the house to the weather while the electrical, plumbing and mechanical rough-ins run inside. Joinery, stone, tiling and paint follow, with fixtures installed, commissioned and tested room by room before handover. A duplex simply carries that sequence across two homes and the party wall between them.

What comes before construction starts

Design is the first stage and its length follows the brief and the site. A duplex asks more of the early stages than a single home. Two layouts, a party wall, two entries and two sets of outdoor spaces all have to work together within the council's controls.

Approval is next. NSW Planning says a complying development certificate can be issued in as little as 20 days where a proposal meets every standard in the code. It compares that with an average determination time of 70 days for a development application. The Low Rise Housing Diversity Code lets dual occupancies use that fast track route in zones where they are already permitted. Our guide to choosing between a DA or CDC explains which sites qualify.

Before we break ground we lock the program, order long-lead items (materials and fittings with long delivery times) and confirm the contract sum. Demolition and protection works are planned around the street and the neighbours, so you know the timeline and the number before the first truck arrives.

What can change the program

A basement is the clearest change, adding three to four months on its own. The approval path is another, since a council assessment usually runs longer than complying development and its conditions may need answering before construction. Sydney Water servicing can also shape the dates. For coordinator applications Sydney Water says it issues a Notice of Requirements within 60 days. Any works it requires must then be built and inspected before the certificate is issued. Our guide to the Section 73 certificate for a duplex covers that sequence.

Changes during the build affect timing too, which is why we hold walkthroughs while a change is still a conversation rather than a variation. The NSW Government's guidance on home building delays points to material and skilled worker shortages and suggests agreeing reasonable allowances for start and finish dates before you sign. If dates do slip, our guide to what happens if a builder does not finish on time explains your contract rights.

What happens after handover

You need an occupation certificate before either home can be lived in. Councils generally won't issue one for new homes until Sydney Water has issued its Section 73 certificate. If the two homes are to be sold or held on separate titles, the subdivision continues alongside the build. Our guide to whether a dual occupancy can be sold separately sets out the title options.

A guided handover then walks you through each home, its systems and its warranties. We return at three, six and twelve months to attend to settlement and defects. To talk about the program for your own site, explore our duplex builders in Sydney.