Why This Article Exists
The most common question we get is some version of “how much does one of these cost?” It sounds simple. It isn’t.
The problem is that most companies in this space answer the question in one of two ways. They either give you a single headline number that doesn’t include half the actual costs, or they say “it depends” and make you fill out a form before they’ll tell you anything useful.
Both approaches waste your time. The first sets you up for a budget shock halfway through the project. The second assumes you’re ready to talk to a salesperson when you’re still trying to figure out if this is even financially feasible.
So here’s the honest version. A secondary dwelling in Queensland typically costs between $150,000 and $300,000 all in — from initial site assessment through to a finished, certified, liveable building. That range is wide because the dwelling itself is only part of the total cost. The site is the other part, and sites vary enormously.
This article breaks down exactly where that money goes.
The Two Halves of the Cost
Every secondary dwelling project has two distinct cost components, and understanding the difference between them is the single most important thing you can do before committing to a build.
The dwelling cost — what the building itself costs to design, manufacture and deliver. This is the predictable part. A well-run builder or modular company should be able to give you a fixed price for the dwelling based on the model, size and specification you choose. If they can’t, that’s a warning sign.
The site cost — everything that needs to happen on your land before, during and after the dwelling arrives. This is the variable part. It depends on your soil, your slope, your existing services, your access, your council area, and whether any overlays (bushfire, flooding, vegetation) apply to your property.
The dwelling cost is a product decision. The site cost is an engineering and logistics decision. They’re quoted separately because they’re driven by completely different factors — and any company that bundles them into a single number before visiting your site is either guessing or hiding something.
Part 1: The Dwelling
The dwelling is the building itself — structure, cladding, insulation, internal fit-out, kitchen, bathroom, flooring, fixtures, electrical, plumbing. Everything from the slab up.
For a Class 1a secondary dwelling in Queensland built to current NCC standards, expect to pay somewhere in these ranges based on size:
| Dwelling Size | Typical Cost Range | What You Get |
|---|---|---|
| 20–35m² (studio/1-bed) | $80,000–$130,000 | Open-plan studio or compact one-bedroom. Kitchen, bathroom, living/sleeping area. Suits home office, single occupant or couple. |
| 35–55m² (1–2 bed) | $130,000–$180,000 | Separated bedroom(s), proper kitchen, bathroom, living area. Genuine independent living for one or two people. |
| 55–80m² (2–3 bed) | $170,000–$250,000+ | Full micro-home proportions. Two or three bedrooms, proper circulation, kitchen that doesn’t feel compromised. Suits a family or high-spec rental. |
These ranges reflect the current Queensland market for purpose-built modular and site-built secondary dwellings using standard residential materials — steel and timber framing, insulated wall and ceiling panels, compliant glazing, residential-grade kitchen and bathroom fit-out.
The per-square-metre cost for secondary dwellings in Queensland currently sits between $2,000 and $3,500/m², depending on specification level. That’s higher per square metre than a standard house, and there’s a reason for it: fixed costs. Every secondary dwelling needs a kitchen, a bathroom, a switchboard, a hot water system, plumbing rough-in, electrical fit-out, and compliance certification — whether it’s 25m² or 75m². Those fixed costs get spread across less floor area, which pushes the per-metre rate up.
This is normal. It doesn’t mean you’re being overcharged. It means small buildings cost more per square metre than big ones. Always have.
What affects the dwelling price
Size — the most obvious variable. A 30m² studio costs less than a 60m² two-bedroom, but not half as much, because of those fixed costs.
Specification level — a basic fit-out with laminate benchtops and standard fixtures costs less than stone benchtops, architectural tiles and brushed brass tapware. Both are valid choices. The difference can be $15,000–$30,000 on a mid-size dwelling.
Build method — modular (factory-built, delivered complete) versus site-built (constructed on your land from scratch). Modular typically delivers faster with less site disruption but may cost slightly more upfront. Site-built offers more customisation but introduces weather delays, longer timelines and more coordination between trades.
Transport and crane — for modular buildings, delivery and crane placement is a real cost. It varies based on distance from the factory, site access and crane requirements. Budget $8,000–$20,000 for transport and crane on a typical SEQ project. Acreage with good access will be at the lower end. Tight suburban sites or long rural driveways will be higher.
Width — in modular construction, width matters because of transport regulations. A 3.2m-wide module can travel on a standard truck. A 4.0m-wide module needs escort vehicles and route permits, which adds to delivery cost. Wider modules are typically only practical for acreage and rural sites with good road access.
Part 2: The Site
This is where budgets blow out. Not because site costs are unreasonable, but because people don’t plan for them.
Site costs cover everything that needs to happen on your land to receive and support the dwelling. The range is wide — from as little as $15,000 on a flat suburban lot with existing services, to $60,000 or more on a sloping acreage block with reactive soil, no sewer, and limited road access.
Here’s what’s typically included:
Soil test and site survey — $800–$3,000
A geotechnical soil test determines the classification of your soil (how reactive it is, how much it moves with moisture changes) and what type of foundation the dwelling needs. This isn’t optional. It’s one of the first things that needs to happen, because the soil classification directly affects the slab design and therefore the cost.
A contour and feature survey maps your site — levels, boundaries, trees, existing structures, services. Your engineer and certifier need this to design the foundation and confirm setback compliance.
On a straightforward suburban lot, expect $800–$1,500 for both. On rural land with complex terrain or erosion management overlays, it can reach $3,000–$6,000.
Slab or foundation — $8,000–$25,000
Most secondary dwellings in SEQ sit on either a concrete slab or engineered piers (stumps). The choice depends on your soil, your slope, and whether your site is in a flood overlay.
A slab on a flat, stable site (Class A or S soil) is the simplest and cheapest option — typically $8,000–$15,000 for a standard secondary dwelling footprint. Reactive clay soils (Class M, H1 or H2 — common across much of SEQ) require a more engineered slab with deeper beams, which pushes the cost to $12,000–$20,000.
Piers are often the better choice on sloping sites, flood-prone land, or where you want to minimise ground disturbance. They’re also easier for running services underneath. Budget $10,000–$25,000 depending on the number of piers, depth, and structural engineering requirements.
Services connection — $5,000–$25,000
Your secondary dwelling needs to connect to water, sewer (or on-site wastewater), electricity, and possibly gas and telecommunications. The cost depends almost entirely on distance — how far the dwelling sits from existing service connection points on your property.
Electrical — if you’re within 30 metres of the main switchboard and your existing supply has capacity, a sub-board and cable run might cost $3,000–$6,000. If you need a new meter or a supply upgrade (common on older properties), it can reach $8,000–$15,000. Energex/Ergon application fees and connection charges apply on top.
Water and sewer — on a suburban lot connected to town water and sewer, extending services to a secondary dwelling typically costs $3,000–$8,000. On rural land with tank water and on-site wastewater (septic), you may need a new or upgraded system. An on-site wastewater assessment and system can cost $5,000–$15,000 depending on soil permeability and council requirements.
Stormwater — your secondary dwelling creates additional impervious area on the lot. Most councils require you to manage stormwater from the new building — either connecting to the existing stormwater system or installing on-site detention. Budget $2,000–$5,000.
Site preparation — $2,000–$15,000
This covers clearing, levelling, access for construction vehicles, and any earthworks needed before the foundation goes in. On a flat, clear site with good access, it’s minimal — $2,000–$5,000 for a basic scrape and level. On a sloping site that needs cut-and-fill, retaining walls or tree removal, it escalates quickly. Retaining walls alone can cost $5,000–$15,000 depending on height and length.
Driveway and access — $0–$15,000
If your secondary dwelling uses the existing driveway and there’s adequate access for construction vehicles (and later, for the occupant’s car), this cost can be zero. If you need a new or extended driveway, a turning area, or a dedicated car park (some councils require an additional parking space for a secondary dwelling), budget accordingly. A basic gravel driveway extension on acreage might cost $3,000–$5,000. A concrete driveway on a suburban lot can run $8,000–$15,000.
Part 3: Council Fees and Approvals
The approval cost for a secondary dwelling depends on whether your project qualifies as Accepted Development (self-assessable against the planning scheme) or requires a Development Application (DA).
Most secondary dwellings that comply with the size limits, setbacks and siting rules in their local planning scheme will be Accepted Development — meaning you need building approval from a private certifier, but you don’t need to lodge a separate planning application with council.
| Fee Type | Typical Range | Notes |
|---|---|---|
| Building approval (private certifier) | $3,000–$6,000 | Covers plan assessment, inspections during construction, and final certification. Required for all secondary dwellings. |
| Plumbing approval | $500–$1,500 | Separate from building approval. Covers plumbing and drainage compliance. |
| QBCC insurance (if applicable) | $1,500–$3,500 | Required for residential building work over $3,300. Covers structural defects for 6.5 years and non-structural for 12 months. |
| Development Application (if triggered) | $3,000–$10,000+ | Only required if your project doesn’t meet Accepted Development criteria — usually because of overlays, non-compliance with size/setback rules, or site-specific triggers. |
| Town planner (if DA required) | $3,000–$8,000 | Professional fees to prepare and lodge the DA. Not needed for Accepted Development. |
| Structural engineering | $2,000–$5,000 | RPEQ-certified structural design for the foundation and tie-downs. Required regardless of approval pathway. |
| Energy assessment (NatHERS) | $500–$1,500 | Required to demonstrate compliance with energy efficiency provisions. Modular builders often include this in their price. |
For a straightforward Accepted Development secondary dwelling, total approval and professional fees typically sit between $6,000 and $15,000. If a DA is triggered, add another $6,000–$18,000 for the application, consultant fees and extended timeframe.
Part 4: Infrastructure Charges
This is the line item that catches people off guard. Infrastructure charges are levied by some councils to fund roads, water, sewer and stormwater infrastructure. Whether they apply to your secondary dwelling — and how much they cost — depends entirely on your council area.
| Council | Infrastructure Charges for Secondary Dwellings |
|---|---|
| Brisbane | Generally no charges for compliant secondary dwellings (Accepted Development). Charges may apply if a DA is required. |
| Moreton Bay | Generally no charges for compliant secondary dwellings following the October 2024 amendment. Previously charged in some circumstances. |
| Gold Coast | May apply. Check with council — charges can range from $15,000–$28,000 depending on the infrastructure networks serving the lot. |
| Logan | May apply above certain size thresholds. Contact council for current schedule. |
| Sunshine Coast | May apply. Council assesses on a case-by-case basis. Can be $15,000–$25,000. |
| Ipswich | Generally no charges for compliant auxiliary units (Ipswich’s term for secondary dwellings). |
| Redland | May apply above certain thresholds. Council is currently reviewing policy (Major Amendment 02/25 underway). |
| Noosa | May apply. Contact council for current schedule. |
Why this matters: A $20,000 infrastructure charge can turn a feasible project into a marginal one. Always confirm infrastructure charges with your council before committing to a build. This is one of the first things to check — not one of the last.
Part 5: The Costs Nobody Warns You About
These are the line items that don’t appear in any brochure, and they’re the reason the gap between “the quote” and “what I actually spent” can be $20,000–$40,000.
Power supply upgrade
Older properties — especially pre-1990 homes and rural properties — often don’t have enough electrical capacity to support a second dwelling. If Energex or Ergon determines your supply needs an upgrade, that’s your cost. It can range from $3,000 for a simple switchboard upgrade to $10,000–$15,000 for a new service run from the street. On rural properties where the supply line is a long distance from the road, it can be significantly more.
On-site wastewater
If your property isn’t connected to town sewer — common on acreage and rural residential land — you’ll need an on-site wastewater system for the secondary dwelling. This might mean upgrading your existing septic to handle the additional load, or installing a new system. An on-site wastewater report (required by council) costs $1,500–$3,000. A new treatment system with land application area can cost $8,000–$20,000 installed.
Bushfire (BAL) compliance
If your property is in a bushfire overlay (common on acreage in SEQ), the dwelling may need to meet a specific Bushfire Attack Level. BAL-12.5 adds minimal cost to the build. BAL-19 and BAL-29 start requiring upgraded glazing, ember guards, non-combustible materials and specific construction detailing that can add $5,000–$20,000 to the dwelling cost. BAL-40 and BAL-FZ (Flame Zone) are significantly more expensive and may affect the feasibility of the project.
A BAL assessment costs $800–$2,000 and should be done early — before you commit to a design or a contract.
Flood and stormwater management
Properties in flood overlays may require the dwelling to be elevated above the Defined Flood Level. This affects foundation design and cost. In some cases, a hydraulic report is required — budget $2,000–$5,000 for the report, plus additional foundation costs.
Tree removal and vegetation management
If significant trees sit where you want to place the dwelling, removal may require council approval. Protected vegetation under State or council codes can’t just be cleared — and the assessment and offset process can cost $2,000–$8,000 if it triggers a referral. This is worth checking very early in the process.
Landscaping and reinstatement
After the dwelling is placed and the construction traffic leaves, your site needs finishing — paths, turf or ground cover, screening plants, fencing between the dwellings if needed. This isn’t a compliance cost, but it’s a real one. Budget $3,000–$10,000 for basic landscaping around the dwelling.
Temporary fencing, skip bins and site amenities
During construction, you’ll typically need temporary fencing ($1,000–$2,000), skip bins for waste removal ($500–$1,500), and potentially a portable toilet if the main house bathroom isn’t accessible from the site. These are small numbers individually but they add up.
Putting It All Together
Here’s a realistic total cost framework for a secondary dwelling project in South East Queensland, broken into three scenarios:
| Cost Component | Straightforward Suburban | Typical Acreage | Complex Rural |
|---|---|---|---|
| Dwelling (built, delivered, installed) | $120,000–$160,000 | $150,000–$200,000 | $180,000–$250,000 |
| Foundation (slab or piers) | $8,000–$15,000 | $12,000–$20,000 | $15,000–$25,000 |
| Services connection | $5,000–$12,000 | $10,000–$20,000 | $15,000–$30,000 |
| Site preparation | $2,000–$5,000 | $5,000–$12,000 | $8,000–$20,000 |
| Approvals and professional fees | $6,000–$12,000 | $8,000–$15,000 | $10,000–$20,000 |
| Infrastructure charges | $0–$20,000 | $0–$25,000 | $0–$25,000 |
| Additional (BAL, wastewater, landscaping) | $3,000–$8,000 | $5,000–$20,000 | $10,000–$35,000 |
| Total Range | $150,000–$230,000 | $190,000–$310,000 | $240,000–$400,000+ |
Straightforward suburban — flat lot under 1,000m², connected to town water and sewer, no overlays, good road access, Accepted Development pathway. This is the best-case scenario and it’s less common than people expect.
Typical acreage — 2,000m²+ lot, may need on-site wastewater, possible bushfire overlay, longer service runs, wider access. This is the most common scenario for the projects we see.
Complex rural — large rural lot, significant slope or reactive soil, limited road access, BAL-29 or higher, new wastewater system, extended power supply. These projects are absolutely viable, but they need more engineering, more approvals and a bigger budget.
The 10% rule: On any secondary dwelling project, hold back 10% of your total budget as contingency. Not because something will definitely go wrong, but because soil surprises, service complications and scope adjustments are normal in construction. A $200,000 project should have $20,000 in reserve. If you don’t use it, you’ve got a landscaping budget.
How to Compare Quotes Properly
If you’re getting quotes from multiple builders or modular companies, here’s what to look for — and what to be cautious about.
Ask what’s included and what’s excluded. A $120,000 quote that excludes transport, crane, slab, services, approval fees and site prep is not a $120,000 project. It’s a $120,000 building that will cost $180,000–$250,000 to get onto your land and make liveable. The headline number is meaningless without a clear scope.
Ask whether the quote is fixed-price or provisional. A fixed-price dwelling contract means the building cost won’t change (assuming you don’t change the scope). Provisional allowances — common for site costs — mean the builder has estimated those costs but the final amount will be adjusted based on actual conditions. Both are legitimate, but you need to know which is which.
Ask about site costs separately. Any responsible builder should want to visit your site (or at least review a soil test and survey) before quoting site costs. If a company gives you a total all-inclusive price before understanding your site, they’re either padding the quote to cover unknowns or they’ll hit you with variations later.
Ask what compliance and certification is included. Some quotes include structural engineering, energy assessment and building certification. Others don’t. Make sure you’re comparing like with like.
Be cautious of prices that seem too low. In the current Queensland market, a fully compliant Class 1a secondary dwelling with kitchen, bathroom, insulation and proper fit-out costs a minimum of about $2,000/m² to build — and that’s at the economy end. If someone is quoting $60,000 for a “complete” two-bedroom secondary dwelling, something is missing from the scope, the specification, or the compliance pathway.
Is It Worth It?
That depends on why you’re building it.
If you’re building for family — to house ageing parents, adult children, or to create genuine multi-generational living — the value isn’t just financial. It’s proximity without sacrifice. A well-built secondary dwelling gives someone their own front door, their own kitchen, their own independence, while staying on the same property. That’s hard to put a dollar figure on.
If you’re building for rental income — the numbers need to work. In SEQ, a well-located, well-finished secondary dwelling can generate $350–$600 per week in rental income depending on area, size, and quality. On a $200,000 total project cost, that’s a gross yield of 9–15%. Factor in property management, maintenance, insurance and the portion of rates attributable to the dwelling, and you’re still looking at strong returns compared to most residential property investments.
If you’re building for property value — a compliant, well-designed secondary dwelling typically adds value to the property at resale. How much depends on the local market and buyer demand. In areas with strong rental demand and limited housing supply — which describes most of SEQ right now — a secondary dwelling with proven rental income is a genuine value-add. But it’s not guaranteed, and it depends on the quality of the build. A cheap, poorly designed annexe can actually hurt a property’s appeal.
The financial case improves significantly if you don’t have to borrow the full amount. Homeowners with equity, redraw facilities, or cash from other sources can fund a secondary dwelling without a separate construction loan — which avoids the complexity and cost of a second mortgage.
Where Outhaus Fits
We build compact, permanent dwellings to Class 1a residential standards. Our pricing is transparent — we quote the dwelling separately from site costs, and we don’t pretend site costs are one-size-fits-all.
We’ll always tell you what we know and what we don’t. We know what our buildings cost. We know what typical site costs look like across SEQ. But we can’t give you a final site cost until we understand your specific property — and neither can anyone else, no matter what they claim.
If you want to understand where your property sits in the cost framework above, the starting point is a conversation. We’ll ask about your site, your council area, your goals, and your budget. If Outhaus is a good fit, we’ll tell you. If it isn’t, we’ll tell you that too.
You can also walk through our completed dwellings at Outhaus Ranch — 472 Laceys Creek Road, Laceys Creek QLD. Three buildings on real land, with real foundations, real services and real costs behind them. No display village polish. Just architecture you can stand in.
Further Reading
- What Is a Secondary Dwelling? (And What Isn’t) — start here if you’re not sure what qualifies
- Secondary Dwelling Size Limits by Council — SEQ 2026 Guide — council-by-council breakdown of what you can build
- Building a Secondary Dwelling on Acreage in SEQ — the full process guide for rural and rural residential properties
- QBCC — check your builder’s licence and understand your insurance protections
This article is general information only. It is not financial, legal, planning or building advice. Costs change, council policies evolve, and every site is different. Get independent advice specific to your situation before committing to a build. All figures are indicative ranges based on the SEQ market as of early 2026 and should not be relied upon as quotations.