General information. This page describes planning rules in general terms, not planning advice for any home or design. Which reading fits a particular building is a question for the council and the state’s planning department: in Victoria, the state’s planning department and the council; in Western Australia, the local government; in Brisbane, Brisbane City Council.
A home with two self-contained parts is read by planning rules in one of two ways: as one dwelling with a smaller second home on the same lot or title, or as two dwellings. Victoria and Western Australia have words for both readings, and Brisbane’s page for the two-home reading. Of these, only Western Australia uses the term, for a dual key dwelling, which its Codes count as one kind of ancillary dwelling.
Victoria: a small second home, or two dwellings on a lot
Victoria has a category for the smaller reading. Its planning department defines a small second home as a dwelling of 60 square metres or less, with a kitchen, a bathroom and a toilet, on the same lot as an existing home. Most properties in residential and rural zones can have one without a planning permit, though a building permit is always needed.
What ties it to the main home is title. The department says a small second home cannot be subdivided, and cannot be sold separately from the main home. So a two-part home read this way stays one property on one title.
The other reading is two dwellings on a lot. Clause 55 of every Victorian planning scheme, the Townhouse and Low-Rise Code, applies to developments of two or more dwellings on a lot, and to residential buildings of up to three storeys. In the residential zones, the department says, a planning permit is always required for these developments.
Western Australia: ancillary, grouped and multiple dwellings
Western Australia’s Residential Design Codes, the R-Codes, set out the words. Volume 1 (the April 2026 version) covers every single house and grouped dwelling development, and multiple dwellings in areas coded R10 to R60; Volume 2 covers apartment developments in areas coded R80 and above, and in R-AC areas.
The smaller reading is the ancillary dwelling: in the Codes’ definitions, a self-contained dwelling on the same site as another dwelling, which can be attached to it, built into it or stand apart from it. The Codes also name a dual key dwelling as one form of ancillary dwelling: a home whose parts open off a shared internal corridor through lockable doors, so that it can be divided into two separate homes. The state’s R-Codes page adds that ancillary dwellings sit on the same title as the main dwelling, and that they can now be built on any residential zoned land, including land with grouped or multiple dwellings and strata lots. One of the Codes’ performance criteria asks that an ancillary dwelling be big enough to live in properly while staying incidental to the main one.
The two-dwelling reading has two words, and which one applies turns on whether one home sits over the other:
- A grouped dwelling is one of two or more dwellings on the same lot where none sits wholly or partly above or below another (unless special conditions of the land’s form or slope call for it). The definition takes in a dwelling in a strata titles scheme with common property.
- A multiple dwelling is one of a group on a lot where part of one home’s plot ratio area is directly above part of another’s.
The Codes’ single house is a dwelling that stands entirely on its own green title or survey-strata lot, and the definition leaves out dwellings on titles with areas held in common property.
Brisbane: dual occupancy
Brisbane City Plan 2014 calls duplex development “dual occupancy”. The council’s page gives the plan’s definition in two parts: the residential use of premises with 2 dwellings on one lot, whether or not they are attached, or 2 dwellings on separate lots that share common property. Both parts are two-dwelling readings.
Brisbane assesses a proposed dual occupancy in one of two ways, code or impact assessment. Only impact assessment brings public notification, which happens before the council decides on the development application; code assessment has none. Once planning approval is in hand, building approval comes next, through a licensed building certifier, with scaled and detailed plans prepared by a draftsperson or architect.
These are Brisbane’s rules, in Brisbane’s plan. Other Queensland councils have their own planning schemes.
The two readings side by side
| Place | One home with a second part | Two homes |
|---|---|---|
| Victoria | Small second home: 60 square metres or less, same lot as an existing home, cannot be subdivided or sold separately | Two or more dwellings on a lot, under clause 55, the Townhouse and Low-Rise Code; a permit is always required in the residential zones |
| Western Australia | Ancillary dwelling: self-contained, on the same site and the same title as the main dwelling; a dual key dwelling is one form of it | Grouped dwelling (side by side) or multiple dwelling (one over another) |
| Brisbane | Not on the council’s dual occupancy page | Dual occupancy: 2 dwellings on one lot, or on separate lots sharing common property |
What the reading changes
The reading decides more than a planning form. In Victoria, a home read as a main home with a small second home stays one saleable property, because the second home cannot be subdivided or sold on its own. In Western Australia, an ancillary dwelling stays on the main dwelling’s title. Where each side is to have its own title, the home is being treated as two dwellings, and the titles are the subject of the next guide.
The approval path differs too. A small second home can be built on most Victorian residential properties without a planning permit, where two dwellings in a residential zone always need one, and in Brisbane, whether a dual occupancy is code or impact assessable decides whether the public is notified.
For the other states and territories, this guide holds no planning source that sorts a two-part home, and says nothing more about them.