A standard knockdown rebuild replaces one house with one house. On the right lot, the same demolition can make room for a duplex: two homes, one to live in and one to sell or rent, or one for each generation.
Does your lot qualify for a duplex?
Four things decide it: the zone, the lot size, the lot width and the approval pathway. Since 1 July 2024, dual occupancies are permitted with consent in the R2 Low Density Residential zone across NSW. Within 800 metres walking distance of nominated town centres, the state's low and mid-rise standards apply, including a 450 m² minimum lot size and 12 m minimum width. Elsewhere, council's LEP and DCP set the numbers. Minimum land size for a duplex works through the Wollongong tests.
How is a knockdown duplex approved?
The demolition, the two new dwellings and, often, the subdivision are dealt with together in one CDC or DA. Each dwelling needs its own BASIX certificate. As with a single home, the existing house stays standing until the approval, contract and insurance are in place.
What doubles compared with a single-home rebuild?
- Services: two water meters, two power supplies, and separate sewer and stormwater where the homes will be on separate titles.
- Driveways and parking: two crossings on a side-by-side duplex, or one long shared driveway on a front-and-back layout.
- Kitchens, bathrooms and laundries: the most expensive rooms per square metre, twice.
- Fire separation: the wall or floor between the two homes must meet the National Construction Code.
Demolition, the site set-up and much of the structure are shared, which is where a duplex gains over two separate builds.
When is the title decided?
Before the design. Torrens title gives each home its own lot; strata keeps shared areas as common property. The choice changes where services, walls and driveways go. Torrens title or strata compares them.
Does a knockdown duplex stack up?
It depends on the lot, the local sale prices and what you plan to do with the second home. The feasibility is worth checking before design starts: compare the build cost of two homes against what each would be worth, and allow for the time the lot earns nothing.
If you own an older house on a wide or deep Illawarra lot, ask a builder that turns Wollongong knockdown sites into duplexes to test the lot and the numbers before you commit to a single-home rebuild. Custom home or project home? covers the design choices that follow.
Sources
Checked on 25 October 2026.
- NSW Planning, Low and Mid-Rise Housing Policy: summary of key provisions: dual occupancy permissibility and standards.
- NSW Planning Portal, BASIX: a BASIX certificate for a new home.
- NSW Department of Planning, Complying development: definition and published approval times.
General information from a builder, not legal or planning advice. Confirm current requirements with your council, certifier or Building Commission NSW.