This is a concept website · Enquire about this domain

Approving a duplex, a guide by Dotto

Designing and approving a duplex

Two homes, one wall, and the duplex rules between them

A guide to designing and approving a duplex, mostly in New South Wales, published by Dotto from the official sources linked on each page. Six pages, set out in three pairs: the planning words, the approval, and the building.

An attached duplex in plan, one home and its mirror A ground floor plan of two attached homes side by side, facing a street at the bottom. The left home is drawn in solid blue ink; the right home is the same plan reflected, drawn in dashed grey pencil. Between them runs a hatched party wall. Each home has a garage and an entry at the front, a kitchen and bathroom in the middle, and living at the back. Party wall, the fold LivingLiving KitchenKitchen EntryEntry BathBath GarageGarage Street Home A, drawn Home B, its mirror
Drawn for this guide: one home and its reflection either side of the shared wall. An illustration only, not a design and not to scale.

Start with the words, or go straight to the page you need. Every rule on these pages links the official page it comes from, and each page says when it was checked.

What the rules call a duplex

In NSW planning terms, a duplex is a dual occupancy: two homes built on one lot of land, attached or detached, and the NSW planning department notes that dual occupancies are often known as duplexes or semis.

In an attached dual occupancy the two homes share a common wall, which the department also calls a partition wall. They usually sit side by side facing the street, and tend to be symmetrical in layout and form, much like the drawing above.

The building code sees the same pair differently. Under the National Construction Code, each home in a group of attached dwellings is its own Class 1a building, separated from the next by a fire-resisting wall. That wall, which the code says may also be known as a party wall, has a page of its own.

A granny flat is a different thing. The department leaves secondary dwellings out of what counts as a dual occupancy, and gives a granny flat as its example, so this guide leaves granny flats aside.

Six pages, folded into three pairs

Each page has a mirror page across the fold: the two read best together.

Pair 1 · The words
What a duplex is in planning termsAttached, detached, semi-detached and the words around them, in NSW and in Queensland.The Low Rise Housing Diversity CodeThe NSW code that lets a duplex be approved as complying development, and what it asks for.
Pair 2 · The approval
DA or CDC: three ways to approve a duplexThe approval routes for a duplex in NSW, and the certificates that follow each one.Telling the neighboursWho must be told, and when, on each route, under the statewide plan.
Pair 3 · The building
The party wall: fire and soundThe separating wall between the two homes, and the services that pass through it.BASIX for a duplexWhich part of the BASIX tool, one certificate or two, and where it goes at each stage.

What has changed in NSW, by date

The rules for a duplex in NSW have moved a good deal in two years. These are the changes the official pages record, oldest first. More are on the way, so check each source before relying on it.

  1. Dual occupancies and semi-detached homes became permitted in the R2 low density residential zone across all of NSW.
  2. New planning controls for dual occupancies and other low and mid-rise housing began in residential zones within 800 metres walk of nominated town centres and stations in Greater Sydney, the Central Coast, the Lower Hunter and Newcastle, and the Illawarra-Shoalhaven.
  3. The Pattern Book Development Code opened the complying development pathway to low-rise designs from the NSW Housing Pattern Book.
  4. NCC 2022 Amendment 2 came into effect, and the NSW Government describes it as the current edition of the building code.
  5. The BASIX tool was upgraded, including the option to put up to 1,000 dwellings, duplexes among them, on a single certificate.
  6. The department exhibited a proposed variations pathway for complying development, and says it will finalise the changes later this year.
  7. A single statewide Community Participation Plan replaced the councils’ own plans, setting when development applications go on public exhibition.
  8. The Planning Portal announced that BASIX certificate numbers are now checked inside the application form before an application can be submitted.
  9. NSW is due to adopt NCC 2025, the new edition of the building code.

Where to look up your own lot

  • Zoning and constraints. The NSW Planning Portal says you can enter your address in its Spatial Viewer to see the planning constraints and zoning rules that affect your property.
  • The low and mid-rise housing areas. The department publishes an indicative map, and says landowners need to check the legislation because the map can’t factor in individual property constraints or local walking networks.
  • A certifier. The Planning Portal links the Building Certifiers Public Register for finding a registered certifier.
  • BASIX. The BASIX tool sits on the Planning Portal, and you log in with a Portal account to use it.

Everything here is general information. A council planner or a registered certifier can tell you how these rules apply to a particular lot.