You've decided you want a second dwelling on the property. Maybe it's for ageing parents, adult kids who aren't leaving anytime soon, a rental to help with the mortgage, or a home office you actually enjoy walking to. Whatever the reason, you're now looking at two very different options being advertised at similar prices, and the marketing on both sides makes it hard to tell what you're actually getting.
The two paths are a traditionally built granny flat and a portable (or transportable) building. Both end up as a permanent second dwelling in your backyard. Both need approvals. Both cost more than the advertised price. But the way you get there, and what you own at the end, is genuinely different.
This is the honest breakdown, based on 2026 pricing across South East Queensland and Sydney, with the regulations and hidden costs both types of builders tend to skim over.
What the terms actually mean
Before we compare prices, let's be precise about what we're comparing. The construction industry uses these terms loosely and it causes confusion.
Traditional granny flat is what most people picture. A licensed builder pours a slab, frames it on your site, does the whole build in your backyard from the ground up. It becomes permanently fixed to your land as a Class 1a dwelling. In Queensland planning speak it's a "secondary dwelling". In NSW it falls under a State Environmental Planning Policy that lets it be approved via Complying Development Certificate on most residential lots.
Portable or transportable building is a Class 1a dwelling built in a factory, trucked to your site, and craned onto footings or piers. It is still a fully compliant residential building. It is not a donga, not a caravan, not a shed with a bed in it. The key legal difference is that it's engineered to be relocated later. You can sell your house and take the dwelling with you if you want to.
There's a third category that muddies the water: kit homes and flat pack builds, where you buy the frame plus cladding and either assemble it yourself or hire trades to put it together on site. These behave more like a traditional build in terms of approvals and permanence, just with a cheaper structural component. We'll touch on these but they're a separate conversation.
The real cost comparison
Advertised prices on both sides are misleading, so let's work with total project costs, which is what actually leaves your bank account. All figures are 2026 South East Queensland and Sydney rates.
Traditional granny flat, built on site
| Size | Spec level | Total project cost |
|---|---|---|
| Studio, 35 to 40 m² | Medium spec | $120,000 to $155,000 |
| 1 bedroom, 45 to 50 m² | Medium spec | $135,000 to $180,000 |
| 2 bedroom, 55 to 60 m² | Medium spec | $165,000 to $220,000 |
| 2 bedroom, 60 m² (max in QLD metro) | High spec | $220,000 to $280,000 |
| 2 bedroom, 60 m² | Premium finishes | $260,000 to $315,000 |
These figures include the slab, structure, weatherproofing, kitchen, bathroom, all internal fitout, standard site works, service connections, and certifier fees. They assume flat ground with reasonable rear access. They exclude the expensive variables like sloping blocks, reactive soils, and long service runs.
Per square metre, expect around $2,200 to $3,300/m² for medium spec, rising to $3,000 to $3,500/m² for high spec. Smaller granny flats always cost more per m² than a full house because the fixed costs of a kitchen, bathroom, and service connections get spread across less floor area.
Portable and transportable buildings
| Size | Fitout level | Building only (delivered) | Total project cost |
|---|---|---|---|
| Studio, 25 to 30 m² | Basic Class 1a | $65,000 to $95,000 | $110,000 to $150,000 |
| 1 bedroom, 35 to 45 m² | Medium spec | $95,000 to $135,000 | $145,000 to $195,000 |
| 2 bedroom, 55 to 60 m² | Medium spec | $130,000 to $180,000 | $180,000 to $240,000 |
| 2 bedroom, 60 m² | High spec | $180,000 to $230,000 | $240,000 to $300,000 |
The "building only" column is what portable builders advertise on their website. The "total project cost" column is what you actually pay. The gap covers what portable manufacturers almost never include in their headline figures:
- Site preparation and earthworks ($3,000 to $15,000 depending on block)
- Concrete footings, piers, or slab ($10,000 to $25,000)
- Transport and crane hire ($4,000 to $12,000, more if access is tight)
- Service connections for water, sewer, stormwater, and electrical ($15,000 to $30,000)
- Building and planning approvals ($3,000 to $10,000)
- External works like paths, decks, and skirting ($5,000 to $20,000)
This is why the "$99k granny flat" ads are misleading. They're quoting the delivered box only.
What the comparison actually looks like
Once you compare like for like, the pricing gap between the two options is smaller than most people think. For a standard 60 m² 2 bedroom dwelling built to a medium spec, you're looking at roughly $180,000 to $220,000 for a traditional build and $180,000 to $240,000 for a portable option, all in.
The portable option can be cheaper at the small end (studio and 1 bedroom) because factory efficiency pays off more on smaller structures. At the 60 m² 2 bedroom size, they end up costing about the same. Above 60 m² you're back into custom territory where the traditional build often wins on value.
Timing: how long until you're renting it out
This is where portable buildings actually have a clear advantage, and it's not marketing spin.
Traditional granny flat timeline (Queensland):
- Design and documentation: 3 to 6 weeks
- Building approval by certifier: 2 to 4 weeks
- Development Application (only if needed): 6 to 12 weeks
- Site start and slab: 2 weeks
- Frame to lockup: 4 to 6 weeks
- Fixing to practical completion: 4 to 6 weeks
- Final inspection and Form 21: 1 week
Total realistic timeline: 4 to 8 months from signing your building contract to handover. Longer if you hit weather delays, a DA is required, or if trade availability is tight in your area.
Portable building timeline:
- Design confirmation and factory scheduling: 2 to 4 weeks
- Approvals in parallel with factory build: 4 to 8 weeks
- Factory manufacture: 6 to 10 weeks
- Site preparation running in parallel: 2 to 4 weeks
- Delivery, crane, and install: 1 to 2 weeks
- Service connections and final inspection: 1 to 2 weeks
Total realistic timeline: 10 to 16 weeks from order to occupancy. The critical advantage is that factory manufacture happens while your site works are being done, and rain doesn't stop the factory. A traditional build stops the moment a storm rolls through.
If you need the space fast, or you're paying interest on a construction loan and every month matters, this is a real financial benefit. Three or four months of saved interest on a $200,000 build at 7% is $3,500 to $4,700 you don't spend.
Approvals: the biggest myth in the industry
The single most common thing we hear from clients is "someone told me a portable building doesn't need council approval because it's not permanent". This is wrong and it gets people into trouble.
Here's the reality across Queensland and NSW:
In Queensland
Every new secondary dwelling on your lot, whether it's a traditional build or a portable structure, requires building approval from a licensed private building certifier. This is not optional. It confirms compliance with the National Construction Code, the Queensland Development Code, and since 1 May 2024, the 7 star NatHERS energy efficiency standard.
Whether you also need a full Development Application from your local council depends on your zoning, overlays, and design. Many councils in South East Queensland (Brisbane, Gold Coast, Sunshine Coast, Moreton Bay) allow secondary dwellings up to 80 m² as "accepted development", which means no DA is required if you meet the setbacks and other criteria. Once you hit any overlay (flood, bushfire, character, heritage) or exceed the size cap, you're into DA territory, which adds two to three months and $3,000 to $8,000 in council fees.
Since September 2022, Queensland has permanently removed the old rule that limited who could live in a secondary dwelling to family members. You can rent your granny flat to anyone on the open market, and the tenant doesn't have to be related to you.
In NSW
NSW is actually simpler in one important way. Under State Environmental Planning Policy (Housing) 2021, most residential lots of 450 m² or larger can approve a secondary dwelling of up to 60 m² via Complying Development Certificate. This is a faster approval pathway that typically clears in 15 to 20 business days and doesn't require a full DA. There's still building work insurance to consider: for any residential building work over $20,000, the builder must hold Home Building Compensation Fund cover through icare.
The point about portable buildings
Portable buildings do not skip either the building approval or the planning approval. They go through the same process. The certifier still has to inspect the placement, the footings, the service connections, and the tie down. The council still applies its zoning and overlay rules to your site.
What changes is the paperwork the manufacturer provides. A reputable portable builder will supply the engineering certificates, structural drawings, energy rating, and tie down design as part of their package. Cheaper portable suppliers won't, and you'll end up paying an engineer separately to make it compliant. This is where "budget" portable deals go sideways.
Property value and resale
This is the argument that comes up in every conversation, and the honest answer is more nuanced than either side of the industry admits.
Traditional granny flats generally add 60 to 80 per cent of their construction cost to your property's market value in South East Queensland and Sydney metro. So a $200,000 build typically lifts your property value by $120,000 to $160,000. In tight suburban markets with strong rental demand (Brisbane's inner north, western Sydney, Gold Coast), that figure can nudge higher. In outer suburbs and regional areas, it's often lower.
Portable buildings on a permanent foundation perform closer to traditional builds than most people assume. If they're installed as Class 1a permanent dwellings, tied down properly, and connected to services, appraisers treat them very similarly to conventionally built dwellings when calculating your property value. Studies of manufactured housing markets show appreciation rates within 1 to 2 per cent of conventional homes over more than 20 years.
The catch is buyer perception. Some buyers still associate "transportable" with "temporary" and discount their offer accordingly. If you plan to sell within five years and you're in a premium suburb where buyers are paying for aesthetic consistency with the main house, this can cost you real money. If you're building for the long haul or as an investment, and especially if you'd consider moving the portable dwelling to a new property later, this concern is largely irrelevant.
There's one scenario where portable buildings genuinely win on economics: if you sell the main property and take the portable dwelling with you to a new site. Traditional granny flats are fixed to your land. Portables are engineered to be lifted, transported, and reinstalled. Relocation costs typically run $8,000 to $18,000 depending on distance and access, but you keep the $150,000+ asset instead of leaving it behind for the new owner to enjoy.
Rental yield and investment return
Rental income is the same for either type of dwelling, assuming similar size and spec. What tenants care about is bedroom count, bathroom quality, storage, and location. They don't care whether the walls were assembled in Ipswich or in your backyard.
2026 weekly rental rates (South East Queensland):
- Studio, 1 bedroom, 35 to 45 m²: $380 to $480 per week
- 2 bedroom, 55 to 60 m²: $450 to $580 per week
- Premium 2 bedroom in inner Brisbane, Gold Coast waterfront: $550 to $680 per week
2026 weekly rental rates (Sydney metro):
- Studio, 1 bedroom, 35 to 45 m²: $450 to $580 per week
- 2 bedroom, 55 to 60 m²: $520 to $680 per week
- Premium 2 bedroom in Eastern Suburbs, Inner West: $680 to $850 per week
On a $200,000 investment renting at $520 per week ($27,040 per year), you're looking at a gross yield of around 13.5 per cent. After council rates, insurance, maintenance, property management fees (if you use an agent), and vacancy allowance, net yield typically lands at 7 to 9 per cent depending on your suburb. That's a substantially better return than the underlying property in most markets.
If you're building for investment, the numbers don't materially change between traditional and portable. The construction method doesn't affect the rent achievable. What affects your return is size, layout, and spec level. A well designed 2 bedroom will always outperform a bigger studio because the target renter market is larger.
When each option genuinely makes sense
Here's how we'd frame the decision after building both types across South East Queensland.
Choose a traditional granny flat built on site when
You want maximum design flexibility, especially matching the existing home's character. Queenslander restoration jobs, heritage character homes, and premium suburban builds usually look wrong with a portable structure sitting next to them.
Your block has awkward access. Portable dwellings need a truck path in and crane clearance, which rules out about a third of inner suburban Brisbane blocks with tight side access or overhead power lines. Building on site has no such limit.
You're holding the property for the long term with no intention to relocate. The permanent build maximises property value and doesn't leave any buyer perception issues.
You want to exceed 60 m² floor area. Above 60 m² you're often into custom design territory anyway and the portable premium starts to lose its logic.
Your soil is reactive or the site slopes significantly. Traditional builds handle these conditions with proper engineered footings and stepped slabs, which portable builders often can't quote confidently without a full geotechnical assessment.
Choose a portable or transportable building when
You need it fast. If time to occupancy matters more than a perfect design match, the 3 to 4 month timeline advantage is real.
You want fixed price certainty from day one. Portable manufacturers can lock in exact pricing because they control the manufacturing environment. Site builds carry more variation risk from weather, unforeseen ground conditions, and material fluctuations.
You want the option to relocate later. This is genuinely valuable if you're approaching retirement and might sell down in a few years, or if you're building for a specific family member who might not need it forever.
The block is a clean flat rectangle with straight access from a rear lane. This is where portable builders make the most sense economically because their delivery and install process is optimised for it.
You're on a rural or regional block far from tradie networks. Traditional builders in remote Queensland and NSW charge premiums for travel time and site allowances. Portable manufacturers absorb these costs into transport, which is often cheaper.
The mistakes we see most often
Comparing the wrong prices. Advertised portable prices exclude site works and utilities. Advertised traditional prices sometimes exclude approvals and finishes. Always ask for a fixed lump sum price that includes everything up to Form 21 (QLD) or Occupation Certificate (NSW). If a builder can't give you that, they're either inexperienced or they're planning to hit you with variations later.
Assuming portable means faster approvals. As covered above, portable buildings need the same building approval and often the same DA as a traditional build. What moves faster is the construction phase, not the paperwork.
Underestimating service connection costs. Long distances from the main house to the granny flat position, deep sewer connections, and lack of existing electrical capacity are all common surprises. A $15,000 service connection assumption can become a $28,000 reality on tricky sites. This applies equally to both build types. Get a plumber and sparky to walk the site before you sign anything.
Ignoring the 7 star NatHERS standard. Since 1 May 2024, all new dwellings in Queensland (including secondary dwellings) must meet a 7 star NatHERS energy rating. Older portable designs that were fine under the 6 star rule now need double glazing, upgraded insulation, and better orientation. If a portable builder is quoting on old plans, verify the energy rating. This shows up as extra cost either way.
Not checking finance implications. Some lenders treat portable dwellings on a different classification for lending calculations, particularly if the manufacturer doesn't provide a Class 1a certification or if the tie down engineering is treated as reversible. If you're borrowing against the finished value, ask your broker or lender specifically about their approach to modular and transportable dwellings before committing. Traditional builds don't have this issue.
Assuming Queensland rules match NSW. The two states have genuinely different approval pathways. NSW's CDC pathway is often faster and cheaper for a 60 m² granny flat than the Queensland accepted development pathway. If you own property in both states, don't assume the process is the same.
A decision framework
If you're still stuck between the two options, work through these questions in order:
What's your maximum size? Above 60 m² in metro areas, favour traditional. At or below, both work.
Is the block flat with truck access? If yes, portable is viable. If no, traditional wins by default.
How's your timeline? Need it in under 4 months? Portable. Comfortable with 6 to 9 months? Traditional gives you more flexibility.
Are you planning to sell or move within 10 years? If you might relocate the dwelling, portable is genuinely useful. If it's staying with the land, traditional protects your resale value better.
What's the main house? Modern brick or contemporary weatherboard? Either works. Character Queenslander or heritage cottage? Traditional builds nearly always look better and add more value.
How comfortable are you with variation risk? Site builds have more moving parts. Portable is more predictable. If you hate financial surprises, that predictability has real value.
The bottom line
There isn't a universal winner in this comparison. The industry likes to frame it as portable versus traditional, but the honest answer is that they're two solutions to slightly different problems.
Portable buildings win on speed, fixed pricing, and flexibility down the track. Traditional granny flats win on design flexibility, resale value in premium markets, and ability to handle awkward sites. Total costs at the 60 m² 2 bedroom sweet spot are within about 10 to 15 per cent of each other once you compare like for like turnkey figures.
If you're building for investment income and speed matters, portable often makes financial sense. If you're building for lasting family use next to a character home in a premium suburb, traditional almost always looks and performs better.
The one thing that isn't different between them is the paperwork. Regardless of which you choose, you'll need building approval from a licensed certifier, planning approval from council if you exceed the accepted development thresholds, service connections certified by licensed trades, and (in NSW over $20,000 or QLD over $3,300) home warranty insurance from the builder. Skipping any of these is illegal and unsellable at resale.
Get three fixed lump sum quotes that include everything to handover. Verify each builder's licence with QBCC (in QLD) or NSW Fair Trading. Ask for their most recent completed project and go visit it. Talk to the owners about what actually happened during the build versus what was promised.
That's how you make a good decision on a $200,000 asset that you're going to own for 20 years.
Harbour Build is a QBCC licensed builder (licence no. 1115030) operating across South East Queensland and NSW (licence no. 275897C). We build traditional granny flats and can quote on portable dwelling installations where the site suits. If you're weighing up the options for a specific block, get in touch or call us on 1300 455 228 for a site assessment and a fixed price quote with no obligation.