Understanding Dual Occupancy and Duplex Developments in Hornsby Shire

As housing demands rise in Sydney, particularly in areas like Hornsby Shire, property owners are exploring options such as dual occupancy and duplex developments to maximise land use and investment returns. Understanding the local regulations and opportunities is crucial for successful development.
 

What Are Dual Occupancy and Duplex Developments?

Dual occupancy refers to two dwellings on a single lot, either attached (sharing a common wall) or detached (separate buildings). A duplex is a specific type of attached dual occupancy, typically mirroring each other, with a shared central wall. 

Understanding Attached and Detached Duplexes

When planning a duplex development, it’s essential to understand the difference between attached and detached duplexes, as each has specific design and zoning requirements.

? Attached Duplex: This is the most common type of dual occupancy, where two dwellings share a common central wall but exist as separate residences. Attached duplexes require less land than detached ones and can be more cost-effective due to shared construction elements such as walls and roofing.

? Detached Duplex: Also known as a freestanding dual occupancy, a detached duplex consists of two separate dwellings on the same lot, without a shared wall. This design provides more privacy and flexibility, making it an attractive option for families or investors looking to create two independent residences on one property. However, detached duplexes require larger land sizes due to additional space needed for separation between dwellings.

Both options offer great investment potential, but choosing the right one depends on lot size, zoning regulations, your development goals and cost. If you’re unsure which is best for your property, Binai Construction can guide you through the process to ensure you maximise your land’s potential.

Recent Changes in Hornsby Shire

As of 1 July 2025, new subdivision standards for dual occupancies and semi-detached dwellings will be implemented in Hornsby Shire. The Department of Planning, Housing, and Infrastructure (DPHI) will incorporate these controls into the Hornsby Local Environmental Plan (HLEP), pending final approvals. Hornsby Council at its meeting on 12 February 2025, nominated the following minimum lot sizes and lot width control for dual occupancy development.

Subdivision Guidelines

Subdivision of dual occupancies in R2 zoned lands is subject to the following: 

For R2 Land not in a Heritage Conservation Zone:

Attached Dual Occupancy:

? Parent Lot: 700 square metres

? Child Lot: 350 square metres

Detached Dual Occupancy:

? Parent Lot: 800 square metres 

? Child Lot: 400 square metres

For R2 Land within a Heritage Conservation Zone:

Attached Dual Occupancy:

? Parent Lot: 800 square metres

? Child Lot: 400 square metres

Detached Dual Occupancy:

? Parent Lot: 900 square metres

? Child Lot: 450 square metres

A minimum frontage width of 16 metres is required for parent lots. These subdivision standards will be enforceable from 1 July 2025. 

CDC Pathway as of 1st of July 2025, excluding Heritage Conservation Zones;

Attached Dual Occupancy:

? Parent Lot: 700 square metres  Minimum Width of 15m

? Child Lot: 350 square metres 

Detached Dual Occupancy:

? Parent Lot: 800 square metres Minimum Width of 15m

? Child Lot: 400 square metres
 

Benefits of Dual Occupancy and Duplex Developments

? Increased Housing Supply: Addresses housing shortages by providing more dwellings.

? Investment Opportunities: Potential for rental income or property sales.

? Efficient Land Use: Maximizes the utility of existing land resources. 

Key Development Standards - For Stage 2 Of The Low and Mid-Rise Housing Policy

For properties within an 800-metre walking distance of Asquith, Hornsby, Thornleigh, Pennant Hills, and Waitara Town Centres and Stations, the following standards apply: 

? Minimum Lot Size: 450 square metres

? Minimum Lot Width: 12 metres

? Applicable Zones: R1, R2, R3, and RU5 
 

These standards align with the Low Rise Housing Diversity Design Guide, facilitating a streamlined approval process through complying development if all criteria are met.  

Lands Restricted from Duplex Development in Hornsby Shire

• In a Transport Oriented Development Area as defined in the Housing SEPP;

• A heritage item or on which a heritage item is located;

• Bush fire-prone land

• Certain flood-prone land or land within flood planning areas in the Hawkesbury Nepean catchment;
  (Note: The Hawkesbury Nepean Catchment is land located north of Castle Hill Road and west of Pennant Hills Road & M1 Motorway)
  (Note: Flood-prone land is based upon the Probable Maximum Flood (PMF))

• In a coastal vulnerability area or a coastal wetlands and littoral rainforests area;

• In an ANEF contour or ANEC contour of 20 or greater; or

• and within a certain distance of certain pipelines.

Navigating the Development Process

Embarking on a dual occupancy or duplex development requires careful planning and adherence to local regulations. Consulting with experienced professionals, such as Binai Construction, can provide valuable insights and guidance tailored to your specific project needs.

Conclusion

Understanding the regulations and opportunities for dual occupancy and duplex developments in Hornsby Shire is essential for property owners and investors. Staying informed about local planning controls ensures that your development aligns with community standards and contributes positively to the housing landscape.

Contact Binai Construction today to discuss your project.