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

There’s no single price for a duplex, because two homes on the same block can cost very different amounts depending on the site, the design and the finishes. What we can do is show you where the money goes, so you can budget properly and compare quotes fairly.

A starting point

Building costs in NSW are the highest in the country. According to Master Builders NSW, the average new detached house in NSW cost about $566,000 to build in 2024/25, or around $2,400 per square metre. A duplex is two homes, so it’s more than one house, but sharing a wall, roof and site works usually makes it cheaper than building two separate houses.

What a turnkey duplex includes

When you compare quotes, check that each one covers the same things. A complete duplex budget includes:

1. Design and consultants: architectural plans, structural engineer, stormwater and hydraulic plans, BASIX, survey and any reports council asks for.
2. Approval: CDC or DA fees, council contributions and Sydney Water (Section 73) costs.
3. Demolition and site works: removing the old house, excavation and any retaining walls.
4. Construction: slab, frame, roof, brickwork and cladding, windows, services and fit-out for both homes.
5. Finishing the site: driveways, fencing, paths and landscaping.
6. Subdivision (if you want separate titles): surveyor and registration costs once the homes are complete.

A low quote that leaves out site works, driveways or landscaping isn’t cheaper; it just moves the cost to later.

What pushes the price up or down

• The site: a sloping block, rock, poor soil or a long stormwater run costs more before anything is built above ground.
• Attached or detached: an attached duplex shares a wall and usually costs less than two separate homes.
• Size and layout: every extra square metre, bathroom and corner adds cost. Simple, efficient shapes build for less.
• Basement or not: a basement can work well on a block that slopes to the street, but it’s one of the biggest single costs.
• Finishes: stone, tapware, flooring and joinery vary enormously. Decide early whether the homes are for you to live in, to rent or to sell, and choose finishes to match.

How to keep the budget under control

• Get your builder involved at design stage. Plans drawn with real building costs in mind avoid expensive redesigns later.
• Lock in your selections before construction starts. Changes once the build is underway are the most common cause of blow-outs.
• Allow a contingency. Something unexpected usually turns up in the ground, especially on older blocks.
• Choose the right approval path. A CDC is usually quicker than a DA, which saves holding costs if you’re paying interest on the land.

Get a realistic price for your block

The only accurate number is one based on your site and your plans. We’ve been designing and building duplexes in Sydney for over 10 years, and we’ll walk you through a realistic budget before you commit to anything. See our duplex building service and recent projects, or check first whether your block suits a duplex.

This article is general information, current as of October 2026. Every project is priced on its own site, plans and selections.