Duplexes: What’s Possible in Sydney Upper North Shore

The Upper North Shore of Sydney, encompassing councils like Hornsby and Ku-ring-gai, is experiencing a transformation in residential development. With recent changes in NSW housing policies, duplex developments have become a viable option for homeowners and investors seeking to maximise land use and property value.
 

Understanding Duplex Developments

A duplex is a residential building comprising two separate dwellings on a single lot, either sharing a common wall (attached) or as separate structures (detached). This form of housing offers flexibility for multi-generational living, rental income, or property resale.
 

Zoning and Planning Regulations

In NSW, the permissibility of duplex developments largely depends on the zoning of the land. The primary residential zones include:

• R1 General Residential

• R2 Low-Density Residential

• R3 Medium-Density Residential

• R4 High-Density Residential

• RU5 Village

Recent reforms have expanded the potential, making duplex developments permissible in all R2 zones.
 

Minimum Lot Size and Width Requirements

The NSW Government’s Low and Mid-Rise Housing Policy stipulates the following minimum requirements for duplex developments:

• Minimum Lot Size: 450 square metres

• Minimum Lot Width: 12 metres

• Floor space ratio: max 0.65:1

• Height of building: max 9.5 m

• Car parking: 1 space per dwelling

• Subdivision allowable in R1, R2 and R3 Zones only min 225 m² per lot / 6 m width per lot

These standards apply to properties within 800 metres of 171 designated town centres and transport hubs, facilitating increased housing density in well-connected areas.
 

Approval Pathways: DA vs. CDC

There are two primary approval pathways for duplex developments:

1. Development Application (DA): A traditional route involving a comprehensive assessment by the local council.

2. Complying Development Certificate (CDC): A streamlined process for developments that meet specific criteria, allowing for faster approvals.

As of July 2025, the CDC pathway will be available for duplex developments in R2 zones, provided they meet the stipulated standards.
 

Local Council Considerations

While state policies provide a framework, local councils are the approval authority and impose additional requirements:

For Hornsby Shire Council:

• You need 700 sqm for the attached dwelling and 800 square meters for the detached duplex with 16 meters frontage for developments in R2 zones.

• If you are in a heritage conservation zone you need 800 sqm for the attached dwelling and 900 square meters for the detached duplex with 16 meters frontage for duplex developments in R2 zones 

The 16m Frontages are measured at the building line, allowing battleaxe properties to be developed into duplex's.

For Ku-ring-gai Council:

• For an Attached or Detached Duplex, you will need 1015 sqm with a lot width of 18m.

Ku-rin-gai Council is still currently finalising development controls for duplexes, and we will update you as soon as we get confirmation.

It’s essential to consult with the respective council and a professional builder to understand the specific requirements for your property.

Benefits of Duplex Developments

• Maximised Land Use: Efficient utilisation of land in high-demand areas.

• Maximise your Financial Options: Live in one, sell one to pay down your debt, live in one and rent one for cash flow, or cash in and sell both

• Increased Property Value: Potential for higher returns through rental income or resale.

• Flexible Living Arrangements: Suitable for extended families or as separate dwellings for rental purposes.

Conclusion

Duplex developments in Sydney’s Upper North Shore present an excellent opportunity for homeowners and investors to capitalise on recent housing policy reforms. Understanding zoning regulations, minimum lot requirements, and approval pathways is crucial. Engaging with experienced builders, like Binai Construction, can provide valuable guidance through the development process.