How Long Does It Take to Build a Duplex in Sydney?

A standard duplex in Sydney takes 12 to 18 months from start to finish. That breaks down to 3 to 6 months for approvals and pre-construction, plus 8 to 12 months for the physical build.

A 4-bedroom double-storey design typically lands closer to the 18-month mark, while a single-storey duplex with simpler finishes can come in faster.

The biggest delay isn’t usually the building, it’s the paperwork. Here is your roadmap to navigating both.

This phase catches most people off guard. Before a single shovel hits dirt, you’ll spend months on design, surveying, and approvals.

Your architect or building designer will need:

• A detailed site survey
• Soil testing (essential for Sydney’s varied geology)
• Concept drawings and working drawings
• BASIX certificate (mandatory in NSW)

This decision can add or subtract months from your timeline.

A Development Application (DA) goes through your local council. In Sydney, particularly in areas like the Inner West, Northern Beaches, or Canterbury-Bankstown, DA processing times regularly blow out to 3 to 6 months. Complex sites or neighbour objections push this further.

A Complying Development Certificate (CDC) is assessed by a private certifier against set state criteria. If your site qualifies, you can have approval in 20 business days. That’s potentially 3 months saved.

Not every site qualifies for CDC. You must meet specific minimum land requirements. Heritage overlays, bushfire zones, flood-prone land, and sites near major roads often require a full DA.

Once approvals land and your builder schedules you in, the physical construction follows a predictable sequence.

Site clearing, excavation, plumbing rough-in, and concrete slab pour. Sydney’s clay soils often require engineered slabs, which adds complexity but not significant time.

Timber or steel frame goes up, followed by roof trusses and roofing. This is when your duplex starts looking like a building. Inspections happen at frame stage.

External cladding, windows, and external doors installed. The building is now weatherproof. This triggers a progress payment milestone.

Internal walls, electrical, plumbing fit-off, plastering, cabinetry, tiling, painting, and final fixtures. This phase is where most delays occur due to trade availability.

$2,500 to $4,500+ per square metre for a turnkey build.

Important: These are build costs only. They do not include land purchase, subdivision fees, or council contributions.

Do you own the land?

• No → Add land cost to your budget before proceeding.
• Yes → Proceed.

Is the land already zoned for dual occupancy?

• No → Add $20,000+ for a town planner and factor in rezoning risk. Some Sydney councils are resistant to dual occupancy in certain areas.
• Yes → Proceed.

Action: Check your land zoning today using the NSW Planning Portal. Search your address and confirm dual occupancy is permitted. Do this before you engage an architect.

The two longest phases are typically pre-construction (council approvals) and lock-up to completion (finishing trades).

Why approvals drag: Sydney councils are processing record numbers of applications. Staff shortages and complex planning controls create backlogs. Some councils are worse than others, check recent DA determination times on your council’s website before assuming a standard timeframe.

Why finishing trades drag: Tilers, painters, cabinetmakers, and electricians are in high demand across Sydney. Builders who subcontract to the lowest bidder often get bumped when higher-paying jobs come in. Thankfully, that doesn’t happen here at Jonathan Homes.

The 4-Bedroom Factor
Building a 4-bedroom duplex adds roughly 4 to 6 weeks to the timeline compared to a 3-bedroom layout. The extra square metreage means additional framing, plastering, electrical circuits, and finishing work. It’s not dramatic, but factor it in. Check out our article on What is a Duplex? for further comparisons.

Don’t just ask “How long will it take?” Vet a builder’s honesty with these three questions:

1. “Are you quoting a DA timeline or a CDC timeline?”

If they’re vague, they haven’t properly assessed your site. A good builder will have checked your planning controls before quoting a timeframe.

2. “How many other projects is your site supervisor managing right now?”

If the answer is more than 5, expect delays. Site supervisors stretched across too many builds can’t give your project the attention it needs.

3. “Do you have your own framing and tiling teams, or do you subcontract to the lowest bidder?”

Builders with in-house or long-term trade relationships have more control over scheduling. Those chasing the cheapest subcontractors often face no-shows and quality issues.

Obtain a Section 10.7 Planning Certificate (formerly Section 149) from your local council. This document confirms what you can and cannot build on your site. Cost is typically under $100 and can be ordered online through most Sydney councils.

Contact your bank or mortgage broker specifically about construction loans. These operate differently to standard home loans, you’ll pay interest-only during the build, with funds released in stages as construction progresses. Get pre-approval before you sign a building contract.

Use the script above. Compare their responses, check their licence on the NSW Fair Trading website, and ask for references from duplex projects completed in the last 12 months. Visit a current build site if possible.

Building a duplex in Sydney is a significant undertaking, but the timeline becomes manageable once you understand where delays typically occur. Start your planning early, choose the right approval pathway, and select a custom home builder who can give you honest answers about their capacity.

Ready to get your duplex project moving? Jonathan Homes specialises in duplex builds across Sydney and can guide you through the approval process, timeline planning, and construction. Get in touch for a consultation and take the first step toward your move-in date.