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Duplex and dual occupancy builders
Minimum lot size and frontage rule out most blocks before anything else is decided. And building two dwellings is not the same as being able to sell them separately — subdivision is its own process, with its own timeline and its own approval.
- Licence checked
- Insurance sighted
- Solvency re-checked
When this is the right path, and when it is not
Your block meets the lot size and frontage rules and the zoning permits a second dwelling.
It is not viable where minimum lot size or frontage falls short, and it is a harder project where a character or heritage control applies.
How the job actually runs
- 01Test whether the site permits it
Zone, minimum lot size and frontage decide this, and they vary by council and by address. It is the first question, not a detail.
- 02Decide torrens, strata or neither
Whether the dwellings can be separately titled changes the finance, the sale value and the planning path. Settle it before design.
- 03Design for two, not one twice
Party walls, acoustic separation, separate services and independent access are the things that make a duplex work or fail.
- 04Get the feasibility done properly
A duplex is a small development. Treat it with development discipline — costs, timelines, finance and exit — not house-building optimism.
Where these jobs go wrong
What most often costs people money on a duplex or dual occupancy specifically.
- Assuming the block qualifies
Minimum lot size and frontage rules rule out most blocks. Confirm against the address before you spend money on anything.
- Forgetting the subdivision is a separate process
Building two dwellings and being able to sell them separately are different things with different approvals and different timeframes.
- Under-specifying the party wall
Acoustic and fire separation is regulated and it is the thing occupants complain about. It is not a place to save.
- Ignoring the finance structure
Lenders treat dual occupancy differently to a single house. Talk to a broker before you commit to a build contract.
Duplex, dual occupancy, secondary dwelling: three different things
The words are not interchangeable and the difference is legal
A duplex is usually two dwellings under one roof form on one lot, often designed so each half can be sold separately. A dual occupancy is the planning term several states use for two dwellings on one lot, attached or detached, and it may or may not permit separate titles. A secondary dwelling — granny flat, in ordinary speech — is a smaller dwelling subordinate to the main house, usually with a floor area cap and usually not separately saleable. Which of the three you are actually proposing determines the approval pathway, the contribution charges, the parking requirement and whether the result can ever be sold as two properties. People routinely brief one and get quoted for another.
The zone decides it, and the lot decides whether the zone helps
Permission for two dwellings on a lot comes from the zone, and every state writes it differently: a minimum site area, a minimum frontage, a maximum site coverage, a required private open space per dwelling, and often a separate rule for whether the lot can then be subdivided. A lot can comfortably clear the site area and fail on frontage, which is the most common reason a duplex proposition dies. Establish those numbers against the actual title dimensions before any design work, because they are cheap to check and expensive to discover.
Two dwellings means two of everything, and a wall between them
Separate water, sewer, power and often separate stormwater connections; separate meters; and a party wall that has to meet fire and acoustic requirements as a separating construction rather than as an internal wall. The party wall is where budgets slip, because it is not one wall — it is a construction type with implications for the footings, the roof junction and the services that cannot pass through it. None of this is difficult, but it is a materially different build from one house of the same total floor area.
Selling separately is a survey question, not a building one
If the point of the exercise is two saleable properties, the subdivision or strata pathway has to work from the beginning: the boundary between them has to be capable of being drawn, each dwelling needs its own legal access and services, and the local rules on minimum lot size after subdivision have to be satisfied. Building first and subdividing later is possible and is sometimes the right sequence, but only if the design was set up for it. Retrofitting a title boundary through a building that was not planned for one is the expensive version.
What moves the price
No figures — a number without your site and your specification is a guess. For a duplex and dual occupancy job, these are what actually move it.
- Party wall construction and acoustic rating
- Separate service connections and metering
- Site coverage and landscaping requirements
- Torrens versus strata subdivision costs
- Driveway and parking arrangement
- Council contributions
Where we cover this, and what the planning data says
Typical height limit is the control that most often decides how a duplex and dual occupancy job runs. Read from state planning data.
| Suburb | Council | Typical height limit |
|---|---|---|
| Abbotsford | Canada Bay Council | 8.5m |
| Ashfield | Inner West Council | 8.5m |
| Balmain | Inner West Council | not mapped |
| Burwood | Burwood Council | 11m |
| Canterbury | Canterbury-bankstown Council | 8.5m |
| Croydon | Burwood Council | not mapped |
| Greystanes | Cumberland Council | not mapped |
| Homebush | Strathfield Council | 9.5m |
| Leichhardt | Inner West Council | not mapped |
| Marrickville | Inner West Council | 9.5m |
| Merrylands | Cumberland Council | 9m |
| North Parramatta | City of Parramatta Council | 9m |
| Northmead | City of Parramatta Council | 9m |
| Parramatta | City of Parramatta Council | 11m |
| Pemulwuy | Cumberland Council | not mapped |
| Pendle Hill | Cumberland Council | not mapped |
| Rhodes | Canada Bay Council | 20m |
| Rodd Point | Canada Bay Council | not mapped |
| Rozelle | Inner West Council | not mapped |
| Strathfield | Strathfield Council | 9.5m |
| Westmead | City of Parramatta Council | 11m |
| Chermside | Brisbane City Council | not mapped |
| Nundah | Brisbane City Council | not mapped |
| Taringa | Brisbane City Council | not mapped |
| Upper Kedron | Brisbane City Council | not mapped |
| Collinswood | City of Prospect | not mapped |
| Nailsworth | City of Prospect | not mapped |
| Tea Tree Gully | City of Tea Tree Gully | not mapped |
| Hobart | Hobart | not mapped |
| Launceston | Launceston | not mapped |
| North Hobart | Hobart | not mapped |
| Ascot Vale | Moonee Valley | not mapped |
| Avondale Heights | Moonee Valley | not mapped |
| Brunswick West | Moreland | not mapped |
| Brunswick | Moreland | not mapped |
| Coburg | Moreland | not mapped |
| Diamond Creek | Nillumbik | not mapped |
| Doncaster East | Manningham | not mapped |
| Eaglemont | Banyule | not mapped |
| Eltham | Nillumbik | not mapped |
| Essendon | Moonee Valley | not mapped |
| Glenroy | Moreland | not mapped |
| Hurstbridge | Nillumbik | not mapped |
| Ivanhoe | Banyule | not mapped |
| Lower Plenty | Banyule | not mapped |
| Montmorency | Banyule | not mapped |
| Moonee Ponds | Moonee Valley | not mapped |
| Northcote | Darebin | not mapped |
| Preston | Darebin | not mapped |
| Research | Nillumbik | not mapped |
| Reservoir | Darebin | not mapped |
| Thornbury | Darebin | not mapped |
| Yarrambat | Nillumbik | not mapped |
Suburb-level, read from state planning data. Not a report on any individual block.
What to ask a builder about a duplex or dual occupancy
Specific to this kind of job. The general list is in questions to ask a builder.
- Does this block meet the minimum lot size and frontage for a dual occupancy?
- Will it be torrens, strata or community titled, and when does that happen?
- Have you built a duplex under this council, and what did they push back on?
- How are the party wall, acoustic separation and fire rating detailed?
- If I am selling one side, what does the contract say about staging and access?
Related
Questions people ask
What is the difference between a duplex and a dual occupancy?
The terms are used loosely and differ by state. Broadly a duplex is two attached dwellings; dual occupancy can be attached or detached. What matters is what your council's controls actually permit.
Can I sell one and keep the other?
Only if the site can be subdivided, which is a separate approval to the building permit. Establish that first — it determines whether the project makes sense.
Do I need a builder who has done duplexes?
Strongly recommended. Party walls, dual services and staged occupancy are where inexperience costs money.
The mechanism
One recommendation, not six quotes
We are a builder broker. Every builder passes the Four-Point Builder Check™: licence checked on the state regulator's own register, insurance sighted rather than self-declared, solvency re-checked on a schedule, and confirmed they take on duplex and dual occupancy work in your suburb specifically.
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