Build Under Cost Breakdown: What We Actually Spent
Real figures from our Coorparoo build-under — slab, framing, wet areas, and fit-out — with notes on where costs blew out and where we saved.
Cost guides for Queenslander projects are hard to find. When we were budgeting ours, the best we could find online were vague estimates from builders who wanted a call before they’d give any figures. So here’s our actual breakdown.
All figures are in Australian dollars (AUD) and reflect 2024–2025 pricing in Brisbane. Your project will differ — but this should give you a realistic starting point.
Project scope
- 3-bedroom Queenslander, approximately 180m² footprint (upstairs)
- New ground floor of approximately 160m² (full build-under, not just a small room)
- Coorparoo, inner Brisbane — reasonable access, no extreme constraints
- Owner-builder procurement, all trades contracted directly
Raise and subfloor
| Item | Cost |
|---|---|
| House raising (including temporary works) | $42,000 |
| Structural engineering (raise and subfloor design) | $6,500 |
| Subfloor framing and stumps | $18,000 |
| Subtotal | $66,500 |
The raise quote came in third-lowest of four we received. Cheapest isn’t always best with raisers — we went mid-range with a contractor who had strong references and had worked with our engineer before.
Slab
| Item | Cost |
|---|---|
| Earthworks and excavation | $8,400 |
| Termite barrier (physical, perimeter) | $3,200 |
| Slab formwork and steel | $14,500 |
| Concrete supply and pump | $11,800 |
| Subtotal | $37,900 |
We had a waffle pod slab designed. The engineer’s specification drove the cost — it’s a reactive clay site and the reinforcing wasn’t cheap.
Framing
| Item | Cost |
|---|---|
| External wall framing (90mm stud) | $22,000 |
| Internal wall framing | $8,500 |
| Roof (garage and carport, new) | $14,000 |
| Subtotal | $44,500 |
We used engineered timber (LVL) for the longer spans. It added cost upfront but simplified the framing and reduced future movement.
Rough-in services
| Item | Cost |
|---|---|
| Electrical rough-in (ground floor + upgrade upstairs) | $18,500 |
| Plumbing rough-in (new bathroom, laundry, toilet) | $14,200 |
| HVAC rough-in (ducted to ground floor) | $6,800 |
| Subtotal | $39,500 |
Electrical was the biggest variable. We took the opportunity to bring the upstairs wiring up to current standards at the same time — that added about $5,000 but was absolutely worth it.
External works
| Item | Cost |
|---|---|
| Windows and external doors (ground floor) | $28,000 |
| External cladding (fibre cement, painted) | $12,500 |
| Garage door | $3,400 |
| Subtotal | $43,900 |
Windows were a significant cost. We used double-glazed aluminium-framed windows throughout the new ground floor — more than timber alternatives but better thermally and less maintenance.
Insulation and internal linings
| Item | Cost |
|---|---|
| Wall and ceiling insulation | $7,800 |
| Plasterboard supply and install | $22,000 |
| Subtotal | $29,800 |
Fit-out (ground floor)
| Item | Cost |
|---|---|
| Bathroom fit-out (tiles, fixtures, vanity) | $18,500 |
| Laundry fit-out | $4,200 |
| Flooring (polished concrete — ground floor) | $8,600 |
| Painting (ground floor, internal) | $9,800 |
| Electrical fit-off | $7,200 |
| Plumbing fit-off | $6,400 |
| Subtotal | $54,700 |
Permits and professional fees
| Item | Cost |
|---|---|
| Development approval (DA) | $4,200 |
| Building approval | $3,800 |
| Owner-builder permit | $420 |
| Building certifier (inspections) | $3,600 |
| Additional engineering (variations) | $2,800 |
| Subtotal | $14,820 |
Total build-under cost
| Category | Cost |
|---|---|
| Raise and subfloor | $66,500 |
| Slab | $37,900 |
| Framing | $44,500 |
| Rough-in services | $39,500 |
| External works | $43,900 |
| Insulation and linings | $29,800 |
| Fit-out | $54,700 |
| Permits and fees | $14,820 |
| Total | $331,620 |
What blew out
Electrical. We underestimated the cost of the upstairs upgrade. Budget generously for electrical — it’s rarely cheaper than you hope.
Windows. We priced double-glazed early and thought we had it covered. By the time we ordered, lead times had extended and one supplier had repriced. Shop early and lock in pricing.
Variations on the slab. When the excavation went deeper than expected in one corner (old fill material), the engineer specified additional reinforcing. That cost about $2,200 extra and wasn’t in the original quote.
Where we saved
Owner-builder procurement. Managing the trades ourselves added time and stress, but it saved meaningful money compared to a builder’s margin. We estimate 15–20% off what a fixed-price contract would have been.
Timing our concreter. We booked three months in advance and got a better rate than the spot price at the time we poured.
Polished concrete instead of flooring. Fewer trades, no moisture barrier issues, and genuinely good-looking.
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