Free tool · duplex and dual occupancy
Duplex cost calculator for Sydney (2026)
Estimate the all-in cost of knocking down a house and building a duplex in Sydney. Every rate and allowance comes from the published ranges in AUD Build’s 2026 duplex cost guide, with sources and dates.
Short answer
Building a duplex in Sydney costs about A$700,000 to A$1.8 million for construction of both homes, excluding land. With this calculator, a 2 × 150 m² standard duplex on a CDC comes to about A$890k–A$1.32m all-in, or about A$946k–A$1.43m with Torrens subdivision and a year’s rent at A$800 a week; a 2 × 200 m² mid-range architectural duplex on a sloping block through a DA, with stormwater detention and subdivision, comes to about A$1.50m–A$2.16m. The calculator includes the state Housing and Productivity Contribution, the Sydney Water charge and the long service levy, which most builder guides leave out.
Calculate your estimate
Your estimate
| Item | Range |
|---|
Worked examples
| Scenario | All-in range | Plus 5–15% contingency |
|---|---|---|
| 2 × 150 m² standard duplex, CDC, asbestos allowance, no subdivision, no rent | A$890k–A$1.32m | A$934k–A$1.52m |
| 2 × 150 m² standard duplex, CDC, asbestos allowance, Torrens subdivision, 52 weeks’ rent at A$800 (Greater Sydney median) | A$946k–A$1.43m | A$992k–A$1.63m |
| 2 × 200 m² mid-range architectural duplex, DA, sloping block with OSD, asbestos allowance, Torrens subdivision, no rent | A$1.50m–A$2.16m | A$1.57m–A$2.48m |
Rates and allowances used
| Item | Range used | When it applies |
|---|---|---|
| New home construction (floor area × rate) · Standard | A$2,500–3,200/m² | Always |
| New home construction (floor area × rate) · Mid-range architectural | A$3,200–4,000/m² | Always |
| New home construction (floor area × rate) · Luxury or custom | A$4,000–5,000/m² | Always |
| Demolition of the existing house | A$10k–A$50k | Always |
| Asbestos removal | A$5k–A$25k | If asbestos is present |
| Detail survey and geotechnical report | A$4k–A$8k | Always |
| Architectural design and documentation | A$8k–A$50k | Always |
| Structural engineering | A$3k–A$6k | Always |
| BASIX and NatHERS assessment | A$1k–A$3k | Always |
| Approval: CDC | A$2k–A$5k | CDC route |
| Approval: DA | A$5k–A$15k | DA route |
| Council contributions (one additional dwelling) | A$18k–A$55k | Always |
| Housing and Productivity Contribution (one new dwelling) | A$11k | Always |
| Sydney Water contribution (Sydney Water example) | A$3k | Always |
| Engineered footings on reactive clay (two homes) | A$24k–A$44k | Reactive clay |
| Sloping site: cut, fill and retaining | A$40k–A$90k | Sloping block |
| On-site stormwater detention | A$10k–A$25k | If council requires OSD |
| Service connections for the second home | A$5k–A$15k | Always |
| External works for two homes | A$60k–A$120k | Always |
| Torrens title subdivision | A$15k–A$60k | If you subdivide |
| Long service levy (0.25% of construction) | 0.25% | Always |
| HBC insurance (about 1.16% of construction) | 1.158% | Always |
How the estimate is built
- Construction = total floor area of both homes × the per-m² range for the specification, from Provincial Homes’ published Sydney duplex ranges: A$2,500–3,200 standard, A$3,200–4,000 mid-range architectural, A$4,000–5,000 luxury.
- Every other item uses the low and high ends of the published ranges in the duplex cost guide. Council contributions are shown for one additional dwelling (A$18,000–A$55,000 as builders quote it); some councils charge per dwelling, so ask yours.
- The Housing and Productivity Contribution is about A$10,812 for one net new dwelling in Greater Sydney (1 January 2026 rate), and the Sydney Water charge uses Sydney Water’s worked example of about A$2,950.
- The long service levy is 0.25% of construction; HBC insurance uses icare’s metro base rate of about 1.16%. Rent is weeks × weekly rent. Contingency of 5–15% is shown separately.
- Not included: land, pools, furniture, loan costs, sales or leasing costs and price changes after October 2026. Check whether each quote includes GST.
Questions
How much does it cost to build a duplex in Sydney in 2026?
About A$700,000 to A$1.8 million for construction of both homes, excluding land, according to the published guides compiled in AUD Build’s 2026 duplex cost guide. All-in budgets for a typical 2 × 150 m² knockdown duplex run about A$0.9–1.35 million in Western Sydney and A$1.5–1.8 million in premium council areas, before land and subdivision.
What do duplex quotes usually leave out?
Council contributions, the state Housing and Productivity Contribution, the Sydney Water charge, the long service levy and Torrens subdivision. On a typical knockdown duplex, the state contribution, Sydney Water and the levy together add roughly A$16,000–A$18,000.
How accurate is this calculator?
It gives a budgeting range, not a quote. It adds up the low and high ends of dated, published ranges. Your lot, council, floor area and specification decide the real price.
Does a duplex need a DA?
Not always. If the lot meets the Low Rise Housing Diversity Code standards for zoning, lot size and frontage, a CDC is often possible and usually quicker. Check your lot on the NSW Planning Portal.
How does AUD Build price a duplex?
As a written proposal that separates shared-site works, home A and home B. Materials for both homes come from www.audbuild.net as one order with two separate specifications, and AUD Build clients can log in to check the material unit prices in their quote.
Sources
All ranges, with their sources and dates, are in AUD Build’s 2026 cost guide. Compare builders on the same drawings: see the knockdown rebuild builders and duplex builders comparisons.