Once you know a lot can carry two homes (the minimum land size page covers that), the next question is how to arrange them. There are two basic layouts, and most Illawarra lots favour one clearly.
What are the two duplex layouts?
- Side-by-side: two homes next to each other, each facing the street, sharing a wall down the middle. Each gets its own frontage, driveway and front garden.
- Front-and-back: one home faces the street and the other sits behind it, reached by a driveway down one side. They can be attached or detached.
How does lot width decide the layout?
Width is the first filter. A side-by-side duplex splits the frontage in two, so each home has to work on half the width. Within a low and mid-rise housing area, the state standards set a minimum lot width of 12 m for a dual occupancy and 6 m per lot for a Torrens subdivision. Outside those areas, council's controls apply. Narrow, deep lots usually point to front-and-back; wide, shallow lots point to side-by-side.
How does orientation change things?
On a side-by-side duplex both homes get the same aspect, so a north-facing rear yard benefits both. On a front-and-back duplex the rear home often gets the better light and privacy, while the front home gets the street. Where the street is to the north, the front home's living areas can face the street and the rear home's face its own yard.
What if the lot slopes?
A lot that falls from front to back often suits front-and-back, with each home stepping down the fall. A lot that falls across its width can make side-by-side awkward, because one home sits higher than the other. On steep Illawarra lots the slope can decide everything; building on a sloping block covers what it does to the cost.
How do driveways and outdoor space compare?
Side-by-side means two driveways and two garages on the frontage, which can dominate the street. Front-and-back means one long driveway, which takes garden and deep soil from the side of the lot. Each home also needs its own private outdoor space: under the complying development design guide, at least 16 m² per dwelling, at least 3 m wide, next to the living area.
How does title fit in?
Side-by-side duplexes Torrens-title neatly, with the boundary down the party wall. Front-and-back Torrens titles need an access handle or right of carriageway for the rear lot, and strata is often simpler for them. See Torrens title or strata before choosing.
How do you choose?
| Lot | Usually suits |
|---|---|
| Wide frontage, shallow depth | Side-by-side |
| Narrow frontage, deep lot | Front-and-back |
| Falls front to back | Front-and-back, stepped |
| Corner lot | Side-by-side, one home facing each street |
| Plan to sell both separately | Side-by-side, Torrens title |
I sketch both layouts on every duplex site before recommending one, because the lot usually answers the question quickly. To test your own lot, talk to an Illawarra duplex builder who designs both layouts on sloping and flat lots.
Sources
Checked on 25 October 2026.
- NSW Planning, Low and Mid-Rise Housing Policy: summary of key provisions: dual occupancy permissibility, the non-discretionary standards and subdivision.
- NSW Planning, Low Rise Housing Diversity Design Guide for complying development: principal private open space for dual occupancies (section 2.1L).
General information from a builder, not planning or legal advice. Confirm the controls for your lot with your council, a certifier or a solicitor.