Types of Duplex in NSW

In NSW Planning law, duplexes are not referred to as duplexes! Their legal name is dual occupancy. 

The Standard Instrument Principle Local Environmental Plan defines two types of dual occupancy: 

"dual occupancy (attached) means 2 dwellings on one lot of land that are attached to each other, but does not include a secondary dwelling"

"dual occupancy (detached) means 2 detached dwellings on one lot of land, but does not include a secondary dwelling"

An attached dual occupancy generally consists of two dwellings that share a common wall. The shared wall typically reduces construction costs and maximises land use efficiency. 

A detached dual occupancy features two completely separate dwellings on the same lot. These standalone homes don't share any common walls and are physically separated from each other, offering a more traditional single dwelling feel.

The phrase 'duplex' is used interchangeably in everyday language, but these specific definitions are important in Planning Law as they define explicitly the end land use. Most notably about a dual occupancy, there can never be more than two dwellings on one lot for the land use to be determined as being a dual occupancy.

If you had two Torrens titled lots next to each other however, you could potentially build two dual occupancies (i.e. two houses on one lot and two on the other) resulting in four houses!

Some key differences between attached and detached dual occupancy:

Attached Dual Occupancy:

• While sharing walls and foundations can reduce costs, this isn't always the case
• CDC (Complying Development Certificate) projects often have higher construction costs due to:
  • Increased steel requirements
  • Additional structural timber needs
  • More stringent building specifications
• CDC approval through private certifiers offers significant time advantages
• More cost-effective strategy for larger duplexes where land is scarce

Detached Dual Occupancy:

• Often more financially viable for smaller products on larger blocks
• Greater flexibility in design and construction methods
• Can be more cost-effective when land constraints aren't as high
• Allows for staged construction if needed (in some cases).

Key Considerations for Your Development Strategy:

• Block size and dimensions
• Local land value
• Target market preferences
• Development timeframe priorities
• Building size and specifications
• Approval pathway (CDC vs DA)

Need help assessing your site's Duplex potential? Simply visit our pricing page to find out how you can get clear answers now.