We get asked this question a lot, as property property owners use the same words for very different planning outcomes.
You might say you want to build a second dwelling, second house, granny flat, dual living setup, duplex or dual occupancy. From a planning point of view, those terms do not all mean the same thing.
That difference matters. It can affect whether you need a development application, whether the second home can be separately rented, whether it can ever be separately titled, what infrastructure charges apply and whether the proposal has a realistic chance of approval.
The two most common options are:
- A secondary dwelling, often called a granny flat
- a second dwelling often called a dual occupancy or two dwellings on one lot
They can look similar on paper, but councils assess them differently.
What is a secondary dwelling?
A secondary dwelling is a smaller dwelling on the same lot as the main dwelling. It is used with, and remains subordinate to, the main dwelling. The Queensland Government describes a secondary dwelling as a dwelling that is used in conjunction with, and subordinate to, another dwelling on the same lot. It is usually smaller in size and scale, and it cannot be developed by itself without a main dwelling.
In plain English, this is what most people call a granny flat.
A secondary dwelling may be attached to the main house, detached in the backyard, built under an existing house, or included as part of a larger renovation. It normally has its own kitchen, bathroom, bedroom and living space, but it stays part of the same property.
In Brisbane, Council treats a dwelling house as including either one dwelling, or two dwellings where one is a secondary dwelling. A dwelling house is not a dual occupancy, rooming accommodation, short-term accommodation or multiple dwelling.
The practical takeaway is simple. A secondary dwelling is not a second full house with equal planning status. It is an additional, smaller dwelling that sits under the main dwelling house use.
Can you rent out a granny flat in Queensland?
Yes, in many cases. Queensland changed the rules in September 2022 to remove restrictions on who can live in secondary dwellings. The Queensland Government says the amendment enabled homeowners to rent out secondary dwellings, such as granny flats, to anyone.
That change made secondary dwellings much more attractive for rental income and family accommodation. However, it did not remove the need to comply with local planning scheme requirements, building approval, fire safety, plumbing and other approvals. The State Government also makes clear that new secondary dwellings still require building approval and may still need other development approvals.
This is where many homeowners get caught. The rental rules changed, but the planning controls did not disappear.
What is a second dwelling aka dual occupancy?
A dual occupancy is different. It generally means two dwellings on one lot, or two dwellings on separate lots that share common property. Brisbane City Council describes dual occupancy as the term used in City Plan for duplex development, including premises containing two dwellings on one lot, whether attached or detached, or two dwellings on separate lots sharing common property.
A dual occupancy is normally two dwellings with a more equal role. Each dwelling is often designed for a separate household. They may be attached, like a duplex, or detached, like two houses on one property.
A dual occupancy may have separate entrances, separate garages, separate private open space and separate service connections. It may also form part of a later titling strategy, such as a building format plan or community titles scheme, depending on the site, council area and approval pathway.
The key difference is this:
A secondary dwelling is subordinate to a main dwelling.
A dual occupancy creates two dwellings with a more independent planning function.
Why the wording matters
The phrase “second dwelling” causes confusion because it can mean either option.
Example 1: You own a house in Brisbane and want to add a 60m2 detached granny flat behind it for rental income. That may be a secondary dwelling, provided it meets the relevant City Plan, building and site requirements.
Example 2: You own a large block and want to build another full three-bedroom house at the rear with its own driveway, services, yard and long-term plan for separate ownership. That is much more likely to be a dual occupancy or another assessable residential use, not a simple granny flat.
Example 3: You want to convert the lower level of a raised house into a separate self-contained unit. Depending on the size, layout, access, parking and relationship to the main house, this could be a secondary dwelling. If it functions as a second equal dwelling, Council may treat it differently.
The design intent matters. Councils look beyond what the owner calls it. They assess what the plans actually show.
Secondary dwelling vs dual occupancy comparison
Secondary dwelling:
- Usually smaller than the main house
- Must stay on the same title as the main dwelling
- Usually cannot be sold separately
- Often has size and location limits
- May be accepted development if it meets all requirements
- Still needs building approval
- Can often be rented, subject to compliance
Dual occupancy:
- Two dwellings with more independent use
- May be attached or detached
- Often needs a development application
- May be code assessable or impact assessable, depending on the site
- Can trigger infrastructure charges
- May support a later titling pathway in some cases
- Has stricter planning, parking, design and servicing requirements
In Brisbane, dual occupancy is not treated the same as a secondary dwelling. Brisbane City Council says dual occupancy development will be either code assessable or impact assessable. If it is impact assessable, the application requires public notification before Council makes a decision.
That is a very different pathway to many secondary dwelling projects, which may sit under the dwelling house provisions if they meet the relevant requirements.
For a Brisbane homeowner, a small detached granny flat behind an existing house may be a secondary dwelling. A new pair of attached dwellings on one lot will usually be a dual occupancy. If the site is in a character area, flood overlay, biodiversity overlay, landslide area or another mapped constraint, planning approval may still be required even for work that looks simple. Brisbane Council notes that overlays and neighbourhood plans can add design requirements and other matters to consider.
Logan has its own terminology and local rules. Logan City Council says a secondary dwelling is self-contained, can be beside, behind, below or above the primary dwelling, can be attached or detached, must be on the same lot, must have the same owner, cannot be subdivided and cannot have a separate title.
Logan also applies size limits. Council states that a secondary dwelling is limited to 70m2 if located in a residential zone on a lot less than 1,000m2, or 100m2 otherwise. Infrastructure charges also apply for secondary dwellings in Logan.
Logan also has an “auxiliary unit” pathway, which is termed Dual occupancy (Auxiliary unit) under the Logan Planning Scheme. Logan’s fact sheet explains that an auxiliary unit is on the same lot and under the same ownership, but may be occupied by people who form a separate household to the main dwelling. It must be on a lot of at least 450m2 and has limits on bedrooms, kitchen, living space and size.
This is a good example of why you cannot rely on generic advice. A layout that works as a secondary dwelling in one council area may be assessed differently in Logan.
City of Moreton Bay has very specific secondary dwelling requirements. For example, secondary dwellings in the Suburban neighbourhood precinct or Coastal communities precinct of the General residential zone require a minimum lot size of 600m2 and primary frontage of 12.5 metres. In other applicable precincts, zones or local plans, the minimum lot size may be 450m2 with 10 metres frontage.
Moreton Bay also has tight size limits for secondary dwellings in many residential areas. Council states that the maximum gross floor area is 45m2 on lots between 450m2 and 800m2, and 55m2 on lots greater than 800m2. Rural and rural residential zones allow up to 100m2, subject to the scheme.
Moreton Bay also requires shared services for secondary dwellings, including a single common water connection and meter, electricity connection and meter, wastewater connection or system, street number, letterbox, driveway and pedestrian access point.
That can surprise owners who want a granny flat to feel like a fully separate house. In Moreton Bay, if you design it with separate services, separate frontage behaviour and a separate identity from the street, you may push it away from a secondary dwelling outcome.
For dual occupancy, Moreton Bay makes the distinction clear. Council says a dual occupancy is not a secondary dwelling and that a secondary dwelling is part of a dwelling house. Council also notes that dual occupancy development may be accepted subject to requirements, code assessable or impact assessable depending on the zone, precinct and site circumstances.
Common mistakes property owners make
The most common mistake is assuming that any second self-contained unit is a granny flat.
A second kitchen does not automatically make something lawful. A separate entrance does not automatically make it a dual occupancy. A tenancy agreement does not fix a planning issue. The plans, the use, the size, the siting, the title arrangement and the local planning scheme all matter.
Another mistake is assuming that a secondary dwelling can be sold separately. In most cases, it cannot. It stays part of the same lot. Logan Council says this directly, noting that a secondary dwelling cannot be subdivided and cannot have a separate title.
The third mistake is relying on rules from the wrong council. Brisbane, Logan and Moreton Bay all treat these uses differently. The same plan may have a different approval pathway across council boundaries.
When you may need a town planner
You should get planning advice before finalising plans if:
- You want two dwellings on one lot
- You want to rent out a granny flat
- You want future separate title potential
- The second dwelling is large or detached
- The property is affected by flood, character, biodiversity, bushfire, slope or other overlays
- Your certifier has asked whether a DA is required
Council has issued a show cause notice or compliance letter
A planner can check the zoning, overlays, use definition, assessment pathway, site constraints and approval risk before you spend money on final building plans.
A secondary dwelling is usually the simpler pathway. It suits smaller granny flats, family accommodation, rental studios and compact backyard dwellings where the second dwelling remains subordinate to the main house.
A dual occupancy is a larger planning move. It suits duplexes, two full dwellings, dual living investment projects and sites where separate occupation or future titling is part of the plan.
The wrong label can lead to the wrong design, wrong approval pathway and costly delays.
Before you build, confirm whether your proposal is a secondary dwelling, auxiliary unit, dual occupancy or something else entirely. Go To Town Planning can review your site, check the relevant council rules and confirm the likely approval pathway before you commit to construction drawings.
