How Long Does a Duplex Take to Build in the Illawarra?

The most common question we get on the first call about a duplex is not about cost. It is about time. How long until we can move in. How long until the second dwelling sells. How long until the construction loan stops costing interest every month.

The straight answer for a TAG Homes duplex in the Illawarra is ten to twelve months of construction, slab to handover of both dwellings. That is the number we plan to, build to and hold ourselves to, on coastal blocks in Thirroul and Towradgi just as much as on flat suburban lots in Oak Flats. Here is where the time goes, what happens before a slab is poured, and where duplex builds lose time when they are not run well.

Before Construction Starts

The pre-construction phase covers everything from finalising the design to getting the approval in place to producing the tender documentation the build runs on. If you walk in with approved plans, we go straight to pricing. If the plans are still being drawn, our drafting team finishes them with you first.

Approval comes through one of two pathways. A development application is assessed by the council, Wollongong City Council or Shellharbour City Council for most of our sites and Shoalhaven City Council for Vincentia and the south. A complying development certificate is issued by a private certifier when the block and the design meet the state's standard rules. Where a block qualifies, we advise the complying development pathway over a development application: the certifier assesses the design against fixed rules, so the outcome is predictable and the build can start sooner. For Shoalhaven projects we work with a private certifier in Nowra who knows the local requirements. Which pathway suits your block depends on the zoning, the lot size and the design, and we sort that out with you before the drawings are finalised so the submission is right the first time. Our guide to council approval in Wollongong walks through both pathways.

Tender documentation, the detailed scope and selections schedule that takes the project to a fixed-price contract, runs alongside the approval. We charge a fixed fee for it once a guide price is agreed, and the sooner selections are made, the sooner it is finished.

Ten to Twelve Months of Construction, Slab to Handover

Once the build starts, a TAG Homes duplex runs ten to twelve months from slab to handover. The milestones run in this order: site set-out and footings, then the slab, then the frame, with both halves framed together so the trades work efficiently. Roof and lock-up follow, which is the point where the building is weatherproof. From there the internal trades sweep through both dwellings: plumbing and electrical rough-in, plastering, kitchens and bathrooms, painting and flooring. Practical completion, the final inspections and handover come at the end.

Two halves of a duplex are built in lockstep. The trades come to site once, do both dwellings and move on, which is faster and cheaper than treating the two homes as separate projects. Building the halves at different times costs more and stretches the program.

Where Duplex Builds Lose Time, and Where They Do Not

The biggest time risk in a duplex build is predictable: late selections. Once construction starts, every selection, tiles, tapware, kitchen, joinery, appliances, has to be locked in before the trade needs to order or install it. A selection that drags on pushes the program back by exactly that long. On a TAG Homes build, selections are locked in before the contract is signed, which is the single biggest reason our duplexes finish in ten to twelve months.

Site conditions are the second risk, and only when they are discovered late. A slope or rock that was not accounted for in the geotechnical report, or a flood overlay that changes the floor level, extends a program if it shows up after construction starts. We investigate the ground and the overlays before anything is priced, so the design already allows for them.

Most of our sites are coastal, from Thirroul and Austinmer down to Kiama and Vincentia, and coastal detailing is part of how we build, not an add-on. Corrosion-rated fixings, cladding and roof detail are specified in the design and ordered with everything else, so a beachside duplex runs to the same program as a block in Figtree.

Trade availability across the Illawarra is the third factor. We work with around 35 contractors consistently, so we are not chasing plasterers, tilers and electricians on the open market the way builders with smaller networks sometimes have to. That stability is what keeps the program on track.

How TAG Homes Manages the Duplex Timeline

As an Illawarra duplex builder, TAG Homes has multiple duplex builds running across the region right now, in Woonona and Bulli, with more signed and heading to site. The award winning Henrietta Street duplex in Towradgi recently completed. Running concurrent duplex builds keeps the trades sequenced and the team across the same construction details from one job to the next, which means each new build starts from a position of momentum rather than a cold start.

The fixed-price contract we run holds for the duration of the build, which removes one of the biggest sources of program slippage on duplex projects, the back-and-forth over variations. Selections are locked in before the contract is signed, the scope is detailed in tender documentation, and what is priced is what gets built.

Every TAG Homes build runs on Jack, the latest construction management software built for Australian builders. The schedule, the selections, the purchase orders, the site diary and the client updates sit in one place, so the program is tracked day by day and you can see where your duplex is up to at any point.

TAG Homes is a construction-led builder with our drafting team. Bring your approved plans, or plans you are working on with your own architect or designer, or start from a blank page through our design and construct pathway, and we will take it from there.

Ready to Map Out Your Build Timeline?

If you are planning a duplex in the Illawarra and you want a realistic program for your block and design, give us a call. We will talk through where the project sits today, what the path to handover looks like, and where the time risks are for your site.

Call Grant on 0423 409 212. TAG Homes Pty Ltd, NSW Builder's Licence 369859C. Winner at the 2026 Master Builders NSW Southern Regions Excellence in Building Awards, and 2024 HIA NSW Region Start-up Business winner.

Questions we hear most

How long does a duplex take to build in Wollongong?

Construction takes ten to twelve months from slab to handover of both dwellings on a TAG Homes duplex. Design, approval and tender documentation happen before that, and how long they take depends on where your plans are up to when you call, so the first conversation is about where the project sits today.

Does a duplex take longer to build than a single house?

Surprisingly little longer, despite being two dwellings. Both halves are built in lockstep, so the frame goes up across both together, lock-up covers both, and the internal trades sweep through both at once. You get two homes for a program not far off a single custom home.

Can you fast-track a duplex with a complying development certificate?

Sometimes. The complying development pathway through a private certifier can replace a council development application, but the design has to fit the state policy exactly, so not every duplex qualifies. We can tell you quickly whether the pathway is available for your block.

What is the longest part of a duplex build?

The internal trades phase, between roof-on and handover, is the longest stretch. It is also where program slippage happens on builds that are not run tightly, because late selections, supply delays on tiles or appliances, and the number of trades working in sequence can each add time. Locking in selections before construction starts is the biggest single thing that keeps a duplex on program.