It depends on your block and your council, but the questions are always the same: is the zoning right, is the block big and wide enough, and is anything on the land that rules it out? Here’s the checklist we run through when someone asks us whether they can build a duplex.
1. Check the zoning
Most Sydney houses sit in an R2 Low Density Residential zone. Since July 2024, the NSW Government has allowed dual occupancies (duplexes) in R2 zones across the state with development consent, which opened up many suburbs where they weren’t allowed before. R3 Medium Density zones generally allow them too.
You can look up your zoning for free on the NSW Planning Portal spatial viewer. Type in your address and check the “Land Zoning” layer.
2. Check the lot size and width
This is where most blocks pass or fail, and the numbers change from council to council. A few examples show how much they vary:
- Near train stations: under Stage 2 of the NSW Low and Mid-Rise Housing Policy (from February 2025), mapped areas within about 800 m of certain stations can allow a duplex on a lot of 450 m² with a 12 m width, a 9.5 m height limit and one car space per home (Hornsby Council).
- Hornsby (outside those areas): 700 m² for an attached duplex and 800 m² for a detached one, more in heritage conservation areas.
- Fairfield: 600 m² or 900 m² depending on location (Fairfield City Council).
- Ku-ring-gai: 1,015 m² for most of the area (Ku-ring-gai Council).
Width matters as much as area. A wide block fits two garages, two driveways and better floor plans. If your block is long and narrow, it may still work, but the design has to be smarter.
3. Check for anything that rules the block out
Even with the right zoning and size, some land is excluded or much harder to build on. Look out for:
- a heritage item on the land, or a heritage conservation area
- bushfire-prone or flood-prone land
- easements or sewer and stormwater pipes running through the block
- a steep slope away from the street, which makes drainage harder and may need an easement through a neighbour’s land
A Section 10.7 planning certificate from council lists most of these for your property.
4. CDC or DA: which approval?
There are two ways to get a duplex approved in NSW:
- Complying development certificate (CDC): faster and more predictable. Your block has to meet the state’s Low Rise Housing Diversity Code and your council’s minimum lot size for complying development, and the design has to meet every standard in the code.
- Development application (DA): lodged with council. It takes longer, but it can handle blocks or designs that don’t fit the CDC rules.
Choosing the right path early saves months. We work this out at the start of every project and manage the approval for you.
5. Think about what makes a good duplex block
Being allowed to build is one thing; building something that’s easy to live in, lease or sell is another. Corner blocks, wide frontages, a gentle slope to the street and a north-facing backyard all make a better duplex. We’ve written more on this in Which site is most suitable for a duplex?
Not sure about your block? Send us the address
The rules are detailed and change often, so the quickest answer is to let us look. Send us your address and we’ll check the zoning, size, width and any red flags for free, and tell you honestly whether a duplex makes sense. We’ve built duplexes across Sydney, from Ermington to West Ryde, and handle the whole job from design and approval to handover. See our duplex building service.
This article is general information, current as of October 2026. Planning rules change, so always confirm the controls for your property with your council or a certifier.