A duplex, which NSW planning law calls a dual occupancy, puts two dwellings on a single lot. When the site and the plans satisfy every rule in the state's Low Rise Housing Diversity (LRHD) Code, the project can be approved with a complying development certificate (CDC) rather than a council DA.
What the LRHD Code covers
The LRHD Code sits in Part 3B of the Codes SEPP. It deals with low rise dual occupancies, manor houses and terraces, none higher than two storeys. For a duplex, the dwellings can share a wall or stand apart, provided both sit on one lot. A secondary dwelling such as a granny flat is a separate type of development and falls outside this part of the code.
The code works only in zones R1, R2, R3 or RU5, and only where the planning rules for that land permit a dual occupancy. Sites that are shut out of complying development generally, including heritage items, heritage conservation areas and environmentally sensitive areas, are shut out here too.
Lot and design rules
Your lot needs to reach the council's minimum lot size for dual occupancies, as set in its Local Environmental Plan (LEP). If the LEP gives no figure, the code applies a default of 400 m². There is also a minimum lot width, plus standards covering height, setbacks, floor space, landscaping, parking and privacy.
The application must include a design verification statement. It is prepared by a registered architect, or by a building designer holding BDAA accreditation, confirming that the design is consistent with the state's design guide for this type of housing.
There is no room for near enough. Miss one standard and the CDC route closes, leaving a DA as the way forward.
How the 2024 and 2025 housing reforms fit in
From 1 July 2024, the State Environmental Planning Policy (Housing) 2021 has allowed dual occupancies, with consent, across the R2 zone statewide, even where a council plan used to prohibit them. The state has since set its own minimum standards for dual occupancy DAs in many areas, including a 450 m² lot, a 12 m lot width and a 9.5 m height limit. A council cannot refuse a DA on those grounds if the design meets them.
The complying development rules were adjusted separately, so do not take it for granted that the CDC path is available just because duplexes are now allowed on your street. The LRHD Code's own lot rules, exclusions and design standards keep applying. Get a certifier to check your particular lot early, before the plans are fixed.
The building code side
Under the Building Code of Australia, each dwelling in a side by side duplex is a separate Class 1a building. A separating wall between them has to hold back fire and cut down noise. Where one dwelling is stacked over the other, the building is generally Class 2, which falls outside our registration and needs a certifier qualified for that class. Our guide to The separating wall between duplex homes: fire and sound rules explains the details.
From application to occupation
A typical duplex CDC follows these steps:
- Obtain the planning certificate and a detail survey of the lot.
- Prepare the design, design verification statement, BASIX certificates and engineering.
- A certifier assesses the drawings against the code and, if they comply, issues the CDC.
- Appoint a principal certifier, who inspects the work at each mandatory stage of the build.
- Obtain an occupation certificate before either home is lived in.
Where the LEP allows it, the code can also allow the lot to be subdivided under that CDC. See our duplex and dual occupancy page for how we help, use our plan assessment service to test a design, or request a quote for your CDC.
Local help across NSW
CertifiBuild certifies Class 1 and Class 10 work in 39 council areas. Local rules on these council pages are a good place to start: Burwood Council, Cumberland City Council, Randwick City Council, Sutherland Shire Council, City of Parramatta, City of Ryde.
Suburb pages with local planning notes: Burwood Heights, Chester Hill, Coogee, Engadine, Ermington, Gladesville, Homebush West, Hunters Hill, Lane Cove, Lane Cove North. You can also browse every service area.
Sources
- Codes SEPP Part 3B, Low Rise Housing Diversity (LRHD) Code page, NSW Planning Portal
- LRHD Code FAQs, NSW Department of Planning
- Low and mid-rise housing policy key provisions summary, NSW Department of Planning
- Low and mid-rise housing policy overview, NSW Department of Planning