"How much per square metre?" is the most common question we hear, and the least useful. Two homes of the same size can differ in price by a large margin because of the site they sit on, the shape of the design and the finishes inside. This guide explains what really drives the cost of a custom home and how to build a budget you can rely on.
1. The site
The block is often the biggest hidden cost. Key factors include:
- Slope: sloping sites may need retaining walls, deeper footings, suspended floors or split levels.
- Soil classification: reactive clay or poor ground can mean stiffer slabs, piers or engineered footings.
- Access: narrow streets, steep driveways or limited set-down space slow delivery and craneage.
- Services: long sewer runs, pump-out systems, stormwater detention or a power upgrade all add cost.
- Overlays: flood, bushfire, character or vegetation overlays can bring added design requirements.
2. Size, and the shape of the floor plan
Size matters, but shape matters nearly as much. A compact, rectangular plan with a simple roof costs less per square metre than a sprawling plan with many corners, cantilevers and roof junctions. Every extra corner adds framing, flashing, waterproofing and labour.
3. Structure and engineering
Large open spans, big glazed openings, cantilevered decks and long-span roofs are what give architectural homes their character. They also need steel beams, larger footings and more engineering. That is often money well spent. Ask your design team which structural moves give the most effect for the cost.
4. Number of storeys and wet areas
Two-storey homes need scaffolding, stairs, upper-floor structure and more complex services. Wet areas such as bathrooms, ensuites, laundries and kitchens are among the most expensive rooms per square metre because of plumbing, waterproofing, tiling and joinery. Stacking wet areas above one another helps.
5. Specification and selections
Finishes are where budgets drift. Window and door systems, cladding, flooring, joinery, benchtops, tapware, appliances and lighting all vary widely in price. Choose early, and keep a running total of your selections against the allowances in your budget.
6. Energy performance and services
Queensland's current energy efficiency standard (a 7-star rating for the building shell plus a whole-of-home energy budget) shapes window, insulation and appliance choices. Good passive design such as orientation, shading and cross-ventilation is the most cost-effective way to achieve it. Solar PV, batteries and efficient heat-pump hot water add upfront cost but lower running costs for decades.
7. Fees, approvals and connections
Allow for the costs beyond construction: design and engineering fees, surveys and reports, certification, council fees and infrastructure charges, service connections, home warranty insurance and, where applicable, the QLeave levy. Together these can add up to a meaningful share of the total.
8. Things that often sit outside the build price
Check whether these are included or need their own allowance:
- Landscaping, fencing, driveways and paths
- Pools, outdoor kitchens and decks
- Window furnishings, built-in furniture and AV
- Demolition of an existing house, and any asbestos removal
- Tree removal, retaining and site drainage
Understanding allowances: PC items and provisional sums
Many building contracts include prime cost (PC) items, which are allowances for items not yet chosen (such as tapware or appliances), and provisional sums, which are allowances for work that cannot yet be priced accurately (such as rock excavation). If the final cost is higher than the allowance, you pay the difference, usually plus the builder's margin. Low allowances can make a quote look cheaper than it really is. The more of these you can turn into fixed prices before signing, the more certain your budget becomes.
Building a budget you can trust
- Start from the total. Decide the all-in amount you are comfortable spending, then work backwards.
- Separate the buckets: land, construction, fees and approvals, external works, furniture and fit-out, and contingency.
- Hold a contingency. Keep a contingency in addition to the contract price for unknowns and changes you choose to make. A higher allowance is wise for difficult sites or renovations.
- Estimate at every design stage. Concept, developed design and final documentation should each be checked against the budget.
- Track selections and variations against allowances throughout the build.
Key takeaways
- Price per square metre is a starting point, not a budget.
- Site conditions and plan shape drive cost as much as size does.
- Check how realistic the PC items and provisional sums in any quote are.
- Budget for fees, external works and a contingency from day one.
This guide is general information for homeowners in Queensland and is not legal, financial or technical advice for your specific situation. Regulations, thresholds and council requirements change. Please confirm current requirements with the relevant authority (such as the QBCC or your local council) and your project team.