The Problem with the Words
If you’ve spent any time researching backyard buildings in Queensland, you’ve probably noticed that every company, every council website, every forum thread and every real estate listing uses different language for what seems like the same thing.
Granny flat. Secondary dwelling. Modular home. Auxiliary unit. Accessory dwelling. Prefab. Tiny home. Compact dwelling. Pod.
Some of these are legal definitions. Some are marketing terms. Some are colloquial labels that have stuck around since the 1970s. And the confusion between them isn’t just semantic — it affects your approval pathway, your building standards, your insurance, your council charges, and ultimately what you’re allowed to build and how much it costs.
This article untangles the three terms people confuse most often: granny flat, secondary dwelling and modular home. They overlap, but they’re not the same thing. Understanding the difference is one of the first things worth doing before you spend money on plans, quotes or applications.
Secondary Dwelling — The Legal Term
A secondary dwelling is the planning law definition. It’s the term used in the Queensland Planning Regulation and in every SEQ council planning scheme. When a certifier, a town planner or a council officer talks about what you’re building, this is the word they use.
Under the Queensland Planning Regulation 2017 (as amended in September 2022), a secondary dwelling is:
A dwelling on a lot that is used in conjunction with, but subordinate to, another dwelling on the lot.
That definition carries specific legal requirements:
- Self-contained — kitchen, bathroom, bedroom and living area within the one building
- On the same lot as an existing primary dwelling
- Subordinate — smaller in scale, bulk and visual presence than the primary house
- Same address — shares the address of the main dwelling, can’t be separately titled
- Permanent — a fixed structure on a permanent foundation
- Connected to services — water, sewer (or on-site wastewater), and electricity
If a building meets all of those criteria and complies with the size limits, setbacks and siting rules in the local planning scheme, it typically qualifies as Accepted Development — meaning it needs building approval from a private certifier, but not a separate development application lodged with council.
Since September 2022, a secondary dwelling in Queensland can be rented to anyone on the open market. The old household-member restriction is gone. That’s the change that turned secondary dwellings from a family convenience into a genuine income-producing asset.
Every council has its own size limits. Brisbane allows up to 80m² in residential zones. Moreton Bay allows 45–55m² in suburban areas and up to 100m² on rural land. Ipswich caps it at 50m². The variation is significant, and it’s worth checking before you start designing anything. We’ve published a council-by-council breakdown for all of SEQ if you want the detail.
The key point: “secondary dwelling” is a planning category, not a building type. It tells you about the legal status of the building on the lot — not what it’s made of, how it was built, or what it looks like.
Granny Flat — The Colloquial Label
The term “granny flat” is not a legal definition in Queensland. You won’t find it in the Planning Regulation, and it doesn’t appear in any council planning scheme as a defined use. It’s a colloquial label — shorthand that Australians have used for decades to describe a small dwelling attached to or near a family home, originally built for an elderly parent.
The Queensland Government itself uses “granny flat” in some of its public-facing communications, which adds to the confusion. But when it comes to approvals, building codes and compliance, the term that matters is “secondary dwelling.”
So a granny flat and a secondary dwelling can be the same physical building. The difference is in the framing.
“Secondary dwelling” is precise. It tells a certifier, an insurer, a council officer and a buyer exactly what the building is: a Class 1a dwelling, subordinate to the primary house, compliant with specific planning provisions, built to residential standards.
“Granny flat” is vague. It could mean a compliant Class 1a secondary dwelling with full kitchen and bathroom. It could also mean an illegal bedroom above a garage with a bar fridge, a converted shipping container, a portable cabin on skids, or a fibro annexe built in 1983 without approval. The label doesn’t distinguish between any of these.
That vagueness matters for three reasons.
Insurance
If you tell your insurer you have a “granny flat” and it turns out the building isn’t a compliant, certified secondary dwelling, you may not be covered for damage, liability or loss of rental income. Insurers care about building classification, not what you call it.
Resale
When you sell a property with a secondary dwelling, the buyer’s solicitor and lender will want to see building approval documentation. A certified Class 1a secondary dwelling is an asset. An uncertified “granny flat” is a liability that can reduce the property’s value or block the sale entirely.
Perceived value
This one is subjective, but it’s real. When most people hear “granny flat,” they picture a basic, low-spec annexe — something functional but not desirable. That mental image affects how they value the building before they’ve seen it. It sets expectations at the bottom of the market, regardless of what you’ve actually built.
A secondary dwelling built to Class 1a standards, with steel and timber framing, full insulation, architectural fixtures and considered interior design, is the same building classification as a house. The word “granny flat” doesn’t communicate that. For many buyers and renters, it actively works against it.
Modular Home — The Build Method
A modular home describes how a building is constructed, not what it is under planning law.
Modular construction means the building — or major sections of it — is manufactured off-site in a controlled factory environment, then transported to the site and installed on a prepared foundation. The building arrives substantially complete: framed, clad, insulated, wired, plumbed, painted, tiled, with fixtures and fittings installed. Final connections (power, water, sewer) and any site-specific finishing happen after placement.
A modular home can be many things under planning law. It can be a primary dwelling, a secondary dwelling, a dual occupancy, or a commercial building. The construction method doesn’t determine the planning classification — the use, the size, and the relationship to other buildings on the lot do.
So when someone asks “should I get a modular home or a secondary dwelling?” — the question doesn’t quite make sense. A modular home can be a secondary dwelling. They’re not alternatives; they’re different dimensions of the same project. One is a planning category (secondary dwelling). The other is a construction method (modular).
What modular construction changes
The build method does affect several practical things, even if it doesn’t affect the planning classification.
Build time. A modular secondary dwelling is typically manufactured in 8–16 weeks and installed in a day. Site-built construction of the same dwelling might take 16–30 weeks on-site. The total project timeline from contract to occupancy is usually shorter for modular — though site preparation (slab, services) happens in parallel either way.
Quality control. Factory construction means controlled conditions — no rain delays, consistent temperature for paint and adhesives, fixed workstations, repeatable processes. The same trades work on the same details every day. This tends to produce more consistent quality than site-built construction, where conditions and trades vary from project to project.
Site disruption. A modular building arrives substantially complete and is craned into position. The on-site construction window is days, not months. For homeowners who are living on the property during the build — which is most secondary dwelling clients — this matters. Less noise, less dust, less traffic, and less time with a construction site in the backyard.
Transport constraints. Modular buildings have to travel on roads, which limits their width. In Queensland, a standard heavy vehicle load is 3.5m wide. Buildings up to about 3.2m wide can travel without special permits. Wider modules (3.5m–4.5m) need escort vehicles, route permits and sometimes night transport. This means modular construction works best for compact designs — which aligns naturally with secondary dwelling size limits.
Cost structure. Modular pricing tends to be more predictable because the dwelling cost is fixed at contract. Site costs are still variable. The total cost of a modular secondary dwelling isn’t necessarily cheaper or more expensive than site-built — it depends on the specification, the site, and the builder. But the cost certainty on the dwelling component is typically higher.
The Comparison Table
Here’s how the three terms actually relate to each other:
| Secondary Dwelling | Granny Flat | Modular Home | |
|---|---|---|---|
| What it describes | Planning classification | Colloquial label | Construction method |
| Legal definition in QLD? | Yes — Planning Regulation 2017 | No — informal term | No — industry term |
| Determines approval pathway? | Yes | No | No |
| Determines building standards? | Yes (Class 1a under NCC) | No | No (same standards as site-built) |
| Determines size limits? | Yes (set by council planning scheme) | No | No (but transport width limits apply) |
| Can they overlap? | A secondary dwelling can be modular or site-built | Usually refers to a secondary dwelling | A modular home can be a secondary dwelling, primary dwelling, or other use |
| What councils care about | Size, setbacks, siting, compliance | Whether it actually meets secondary dwelling criteria | That it meets the same NCC standards as any other building |
| What insurers care about | Building classification and certification | Whether it’s actually certified | Same as site-built — Class 1a compliance |
The short version: “secondary dwelling” is what your building is under planning law. “Granny flat” is what your neighbour calls it. “Modular” is how it might be built.
Other Terms You’ll Encounter
While we’re clearing up language, here are a few more terms that get thrown into the mix — and what they actually mean in Queensland.
Dual occupancy
Two independent dwellings of similar size and scale on the same lot. Neither is subordinate to the other. Completely different approval pathway from a secondary dwelling — usually requires a Development Application, higher infrastructure charges (some councils charge $28,000 or more), and different setback requirements. If your secondary dwelling is too large or too visually dominant relative to the main house, a council may reclassify it as a dual occupancy. That’s one of the reasons size limits exist.
Auxiliary unit (Ipswich)
Ipswich City Council uses “auxiliary unit” instead of “secondary dwelling” in its planning scheme. The concept is the same — a subordinate, self-contained dwelling on the same lot as a primary house — but the term and some of the specific provisions differ. Ipswich caps auxiliary units at 50m² and one bedroom, making it one of the most restrictive councils in SEQ.
Tiny home
Not a planning term. “Tiny home” is a lifestyle label that covers everything from architecturally designed micro-houses to converted buses to trailers with composting toilets. Some tiny homes are compliant secondary dwellings. Many are not — particularly the “tiny homes on wheels” that dominate social media. If it has wheels, it’s not a secondary dwelling under Queensland planning law, regardless of how well it’s built.
Prefab
“Prefab” is short for prefabricated — any building where components are manufactured off-site. Technically, modular construction is a type of prefabrication. But in Australia, “prefab” carries connotations that “modular” doesn’t. For many people, “prefab” conjures images of cheap, temporary-feeling buildings from the 1960s and 1970s — the kind that looked tired within a decade. Modern modular construction has very little in common with that era, but the association persists.
Kit home
A kit home is delivered as a set of components — framing, cladding, roofing, windows — that are assembled on-site, usually by the owner or a local builder. Kit homes are not modular homes. A modular home arrives as a finished (or near-finished) building. A kit home arrives as parts. The quality of the final product depends heavily on who assembles it and how well they do it.
Container home
A building constructed from repurposed shipping containers. Some companies market these as secondary dwellings, but getting a shipping container certified as a Class 1a dwelling in Queensland can be difficult and expensive. The underlying structure wasn’t designed to meet residential building standards, and the modifications required to achieve compliance (insulation, fire separation, ventilation, structural reinforcement) can cost as much as building a purpose-designed dwelling from scratch.
Why the Language Matters
This isn’t an exercise in pedantry. The words you use when researching, quoting and building a secondary dwelling have practical consequences.
If you search for “granny flat builder” instead of “secondary dwelling,” you’ll get a different set of results — and those results will often be at the lower end of the market in terms of design quality, construction standards and long-term durability. You’ll also find more operators who play fast with compliance, because the “granny flat” market has historically attracted businesses that treat these buildings as a quick, low-cost product rather than residential architecture.
If you tell your certifier you want to build a “modular home” without specifying that it’s a secondary dwelling, you may start the conversation in the wrong approval pathway — primary dwelling provisions are different from secondary dwelling provisions, and the distinction matters for setbacks, size limits and infrastructure charges.
If you tell your insurer you have a “granny flat” that turns out to be an uncertified structure, you have a coverage problem. If you tell a buyer the same thing, you have a sales problem.
The language doesn’t have to be fancy. It just has to be accurate. “Secondary dwelling” for the planning classification. The specific build method (modular, site-built) when it’s relevant. And “granny flat” only when you’re talking to someone who needs the colloquial reference to understand what you mean — then clarify what the building actually is.
Where Outhaus Fits
We build modular secondary dwellings. That means our buildings are factory-manufactured, transported complete, and craned onto prepared foundations — and they’re designed from the outset to comply with secondary dwelling provisions under the Queensland Planning Regulation.
Every Outhaus dwelling is a Class 1a building — the same residential classification as a house. Steel and timber framing, full insulation, architectural fixtures and fittings, three interior palettes, and a specification level you’d expect in a well-designed home, not a budget annexe.
We don’t call them granny flats. Not because the word is wrong, but because it sets the wrong expectation. When people walk through one of our buildings for the first time, the most common reaction is some version of “this doesn’t feel like what I was expecting.” That gap between expectation and reality is the gap the language creates. We’d rather close it before people arrive.
If you want to see the difference for yourself, visit Outhaus Ranch — 472 Laceys Creek Road, Laceys Creek QLD. Three completed dwellings on a working cattle property, with real foundations, real services and real interiors. No display village staging. Just architecture you can stand in and make your own judgment about.
Further Reading
- What Is a Secondary Dwelling? (And What Isn’t) — the full definition, including what doesn’t qualify
- How Much Does a Secondary Dwelling Cost in Queensland? — transparent cost breakdown: dwelling, site, council fees and hidden costs
- Secondary Dwelling Size Limits by Council — SEQ 2026 Guide — what each council allows, zone by zone
- Building a Secondary Dwelling on Acreage in SEQ — the full process guide for rural and rural residential properties
- Five Reasons People Add an Outhaus — common use cases: multi-generational living, rental income, ageing in place, renovation staging and lifestyle flexibility
This article is general information only. It is not legal, planning or building advice. Regulations change, council schemes vary, and every site is different. Confirm everything with your local council and a qualified building certifier before committing to a build.