What is the minimum lot size for a duplex in Australia? Dual occupancy rules by state

There is no single minimum lot size because different state and council rules apply depending on where the block is located. In New South Wales and Queensland the documented minimums reviewed for this article range from 400 m² on the New South Wales complying-development path to 3,000 m² in Brisbane's Low density residential zone⁴².

Duplex is the everyday word for a pair of homes on one block, and the planning term in New South Wales is dual occupancy, meaning two homes on one lot, either attached or detached. It does not include a granny flat, which is treated as a secondary dwelling⁵. Brisbane's City Plan uses the same term for two dwellings on one lot, whether or not attached, as well as two dwellings on separate lots that share common property⁶.

Up to three sets of rules can affect whether a duplex can be built on a block. The council's planning rules set the zone and, in New South Wales and Queensland, usually the lot-size test. State rules can also override some council requirements. In New South Wales, this has applied in mapped low and mid-rise housing areas since 28 February 2025.⁷ An estate's design guidelines can add another layer and may prevent a duplex from being built on particular lots.

A lot that passes the minimum size may still need to meet other requirements, including width, floor space, height, parking, garden area and design standards. These requirements differ between states.

Victoria's residential zones do not set a minimum lot size for two dwellings on a lot. Instead, a planning permit is generally required. A permit is required to construct two or more dwellings on a lot, or a dwelling where one already exists, regardless of the lot size¹³. Extra controls can still apply to particular land through the local planning scheme.

The application is assessed against Victoria's planning standards for two or more dwellings on a lot¹⁴. Since 31 March 2025, a proposal that meets an applicable standard cannot be refused for failing that standard. If it meets every applicable standard, an objector cannot take the application to the tribunal.

Since 16 October 2025, some applications for two dwellings can use Victoria's faster VicSmart approval process. This applies in residential zones other than the Low Density Residential Zone where the listed standards are met. VicSmart is a 10-business-day permit process with no advertising to neighbours¹⁵.

Lot size still affects how much garden area is required. In the General Residential Zone, an application to construct a dwelling on a lot of 400 to 500 m² must set aside 25 per cent of the lot as garden area. This rises to 30 per cent for lots of more than 500 m² and up to 650 m², and 35 per cent for lots of more than 650 m²¹³. No minimum garden-area percentage applies to lots smaller than 400 m².

Different garden-area rules apply when land is subdivided. A vacant lot of less than 400 m² that could be developed for a dwelling must generally contain at least 25 per cent garden area, although some exceptions apply¹³.

A small second dwelling, Victoria's granny-flat equivalent, is a self-contained dwelling of 60 m² or less on the same lot as an existing home. The Department of Transport and Planning states that in most cases no planning permit is required where no flooding, environmental or other special control applies¹⁶. In the General Residential Zone, a permit is required only on a lot of less than 300 m², and the dwelling cannot be put on a separate lot by subdivision¹³.

In Western Australia, the amount of land required depends on the residential density code for the property. These codes, such as R20, R25 and R30, are shown on local planning maps. On R20-coded land a single house or grouped dwelling needs 350 m² minimum and 450 m² average site area per dwelling³.

Western Australia's planning rules use the term “grouped dwelling” for two or more homes on the same site where one is not built above or below another. The definition also includes dwellings in a strata scheme with common property³.

For two grouped dwellings on R20 land, the 450 m² average means the site would generally need 900 m² in total. Each dwelling must also have at least 350 m² of site area.

These minimum and average areas are set by the Residential Design Codes. Some limited exceptions apply, including cases where the Western Australian Planning Commission approves a lot up to 5 per cent smaller than the minimum because of circumstances, such as protecting a heritage feature or an unusual limitation of the land³.

The minimum lot size for a duplex can depend on up to three sets of rules: council planning rules, state rules and estate requirements.

• Council rules. In New South Wales it is the local environmental plan's lot-size clause for a dual occupancy. In Queensland it is the planning scheme's table of assessment for the zone and precinct. In Victoria local planning controls can add requirements to the state rules. In Western Australia, the residential density code shown on the local planning map helps determine the required site area.
• State rules. In New South Wales it is whether the lot sits in a mapped low and mid-rise housing area, where the 450 m² standard prevails, and which complying path applies. In Victoria it is clause 55 and the VicSmart class. In Western Australia it is the Table D row for the lot's density code.
• Estate rules. The plan of development, design guidelines or lot-specific building rules can add further restrictions. In the Queensland estates reviewed for this article, these rules can determine whether a duplex is allowed on a particular lot.