Inside a residential building contract, the most expensive part of building a house is the structural shell — the site works, footings, slab, frame and roof that get you to lock-up. On the coastal builds we price out of Coolum Beach, nothing else in the contract sum comes close. If you widen the question from the contract to the whole project, land sits outside the contract sum altogether and, in our experience, is frequently the largest single cheque an owner writes on the Sunshine Coast. And if what you are really asking is which line is most likely to cost more than you were quoted, the answer changes again: site works and foundations, because they are priced off a soil test and a survey done before anyone has put a bucket in the ground.
Which answer matters depends on whether you are buying land, signing a contract, or already on site. The ranking below is how the money falls on the jobs we run out of Coolum Beach, across the Sunshine Coast and Noosa Shire.
Ranked: where the money goes in a Sunshine Coast house build
Most cost breakdowns online hand you tidy percentages for the frame, the kitchen and the roof. We have not been able to find a trade-by-trade percentage split of a residential contract sum published by the QBCC, the Australian Bureau of Statistics or Master Builders Queensland, so we have not invented one. Generic national averages do not survive contact with an acid sulfate soil overlay at Cotton Tree or a wind classification on an exposed block at Yaroomba. The table below ranks the cost centres in the order we see them on coastal custom builds, describes the share each one takes, names the driver behind it, and points to the published rule, standard or fee that governs it. The share column is our own experience as a licensed builder, not a published statistic.
| Rank | Cost centre | What sits inside it | Share of the contract sum (our experience, not a published figure) | What moves the number | Published rule or fee that governs it |
|---|---|---|---|---|---|
| 1 | Site works, footings and slab | Excavation, retaining, fill and compaction, piers, raft or waffle slab, stormwater | Largest single block, and the most variable from block to block | Soil classification, fall across the block, rock, groundwater, tree removal, plant access | AS 2870 Residential Slabs and Footings; overlays mapped under Sunshine Coast Council’s Planning Scheme 2014 and Noosa Shire Council’s Noosa Plan 2020 |
| 2 | Frame, roof structure and roofing | Wall frames, trusses, structural steel, battens, sheeting or tiles, gutters and fascia | Second largest block, and fairly predictable once it is engineered | Wind classification, clear spans, cantilevers, roof pitch, marine corrosion category | AS 4055 Wind Loads for Housing; AS 3959 Construction of Buildings in Bushfire-prone Areas where the lot is mapped |
| 3 | Joinery, cabinetry and internal fitout | Kitchen, butler’s pantry, robes, vanities, stairs, feature timber, wall linings | Large, and the widest swing of all — the main reason two houses of the same size land at different prices | How much is bespoke rather than modular; stone, veneer and hardware selections | Not price-regulated — see our kitchen renovation cost guide |
| 4 | Windows, doors and glazing | Window and door suites, stacker and pivot doors, screens, hardware | Moderate, but climbs steeply with glass area on a view block | Glass area, wind rating, marine-grade finishes, thermal performance | National Construction Code 2022, which Business Queensland lists as providing the building and plumbing requirements for new and renovated buildings |
| 5 | Services | Electrical, plumbing and drainage, air conditioning, solar, data, switchboard | Moderate, and comparatively steady across most builds | Length of runs, number of wet areas, connection and metering works | Plumbing and drainage work attracts council fees — Sunshine Coast Council’s Development Services Register of Cost-recovery Fees and Commercial Charges 2026–27 |
| 6 | Wet areas | Waterproofing, screeds, tiling, tapware, sanitaryware, shower sets | Moderate, and scales almost directly with the number of bathrooms | Number of bathrooms, tile format, hobless and linear detailing | AS 3740 Waterproofing of Domestic Wet Areas — see our bathroom cost guide |
| 7 | External works | Driveway, decks, pool and pool surrounds, landscaping, fencing, retaining walls | Anywhere from minor to very large, depending mostly on whether a pool is in scope | Fall on the block, pool structure and shell type, crane or pump access | Queensland’s swimming pool safety laws and pool safety standard, administered by the QBCC, which also holds the pool register |
| 8 | Preliminaries, supervision and margin | Site establishment, scaffold, cranage, waste, insurances, supervision, builder’s margin | Significant, and set mostly by how long the program runs | Program length, site access and constraint, number of trades on site at once | QBCC states home warranty insurance is payable on projects valued at $3,300 and above |
| 9 | Statutory and professional costs | Certifier, engineer, surveyor, energy assessment, approval fees, infrastructure charges | Smallest block, and the one owners most often leave out of a budget | Council area, overlays triggered, whether infrastructure charges apply to the lot | Sunshine Coast Council’s infrastructure charges resolution and cost-recovery fee registers; Noosa Shire Council’s equivalents |
Why site works and foundations blow budgets more than anything else
Rank one is also rank one for surprises. Everything above ground can be measured and priced from a drawing. What is under the slab cannot. A geotechnical engineer classifies the site under AS 2870 Residential Slabs and Footings, and that classification, together with the fall across the block, sets your footing system before a single frame is ordered.
Here the variables are unusually wide. The sand we work in behind the dunes at Marcus Beach and Yaroomba behaves nothing like the ground on the hinterland slopes at Ninderry, and neither behaves like the low-lying flats around Cotton Tree. You can see a coastal sand site in our Kara Court, Yaroomba project. If your block has a noticeable fall, read our guide to building on a sloping block in Queensland before you commit to a design.
If ground conditions do force a change, it has to be handled as a written variation. The QBCC requires the contractor to present the variation to the home owner in writing and the home owner to agree to it in writing, and requires the written copy to be given to the owner before the domestic building part of the variation work starts or within five business days of both parties agreeing to the variation, whichever comes first. The QBCC also states a contractor cannot require payment for a variation before the variation work is started. A builder who says they will sort it out at the end is not following the rules.
The shell is the biggest single package
Frame, roof and roofing sit second only because we have separated them from the substructure. Combined with rank one, the structural shell is the largest share of any coastal contract sum we price.
Two things drive it. Wind first: housing near the coast is designed to a wind classification under AS 4055 Wind Loads for Housing, and moving up a classification means heavier tie-downs, bracing and connections through the whole structure. Corrosion second. Close to open surf you specify higher-grade coatings and fixings, and that flows through roofing, gutters, fascia, screens and every exposed bracket. Neither is a finish you will ever see, which is why they get value-engineered out of cheap quotes and reappear later as a variation.
Fitout is what separates a custom build from a project home
Rank three is where two houses of identical floor area end up at very different contract sums. A modular kitchen and standard robes are a manageable number. A joinery package drawn by an architect in solid timber and stone, with integrated appliances and no repeated cabinet, is a different order of cost — and it is the easiest place to bring a budget back under control without touching the structure. Our custom build versus project home guide works through where that money goes.
The Grandview Drive renovation at Coolum Beach won three 2025 Sunshine Coast Housing & Construction Awards from Master Builders Queensland — Home Renovation/Remodelling Project over $1 million, Best Residential Swimming Pool, and Best Use of Innovation — presented on 15 August 2025 at The Events Centre, Caloundra.
The costs that never show up in a per-square-metre figure
Ranks eight and nine are the ones owners forget. The QBCC states that home warranty insurance only needs to be paid on projects valued at $3,300 and above, and that the insurable value is worked out by adding materials, labour and GST together, excluding the QBCC premium itself.
It buys real protection. The QBCC publishes a maximum of $200,000 under the Queensland Home Warranty Scheme for each of refunding a deposit or completing incomplete work and repairing defects, repairing fire, storm or tempest damage to incomplete work, and fixing defects and subsidence after the work is completed — with a maximum of $5,000 inside that limit for alternative accommodation, removal and storage costs. The QBCC also publishes optional additional cover that lifts those figures to $300,000 and $10,000.
Alongside that sit certification and engineering fees, council building and plumbing lodgement fees from the relevant cost-recovery register, and, where they apply, infrastructure charges levied under your council’s charges resolution. None of it appears in a headline rate per square metre, which is why we treat those rates with caution in our Sunshine Coast build cost guide.
Your contract decides who wears the biggest line
The same house can carry very different risk depending on how it is contracted. The QBCC requires a written contract for domestic building work priced over $3,300 including labour, materials and GST. For renovations, extensions and routine repairs on existing homes it splits those into Level 1 contracts priced at $3,301 to $19,999 and Level 2 contracts priced at $20,000 and over, and where the work is priced at $20,000 or more the contractor must give you a copy of the QBCC consumer building guide before you sign. The QBCC also requires the contractor to give you a copy of the signed and dated contract within five business days of entering the contract, and, on new home and Level 2 contracts, to give you the commencement notice within ten business days of work starting on site.
On cost plus contracts the QBCC is blunt: it strongly recommends both parties obtain formal legal advice before agreeing to use one for domestic building work, it reports that final costs under a cost plus contract are often considerably more than home owners anticipated at the beginning of the project, and it states that assistance for non-completion under the Queensland Home Warranty Scheme is not available to home owners when cost plus or construction management contracts are used. That is the trade-off explained in our guide to fixed price building contracts in Queensland. Before you sign with anyone, check their QBCC licence — ours is 15280811 — and read how we scope and price a job in our build process.
Frequently asked questions
Is the kitchen the most expensive part of building a house?
No. On a custom coastal home the kitchen sits inside the joinery and fitout package, which we rank third. It is usually the most expensive single room, and the most visible place to spend or save, but the structural shell costs more.
What is the most expensive part of a renovation rather than a new build?
Structural alteration — removing load-bearing walls, underpinning, new footings for an extension, and re-roofing. The principle holds either way: the work you cannot see costs the most and carries the most risk.
Why do site costs vary so much between blocks on the Sunshine Coast?
Because soil classification under AS 2870, fall across the site, and the overlays mapped in Sunshine Coast Council’s Planning Scheme 2014 or Noosa Shire Council’s Noosa Plan 2020 change from street to street here. Two blocks on the same street can need very different footing systems.
Can a builder give me a fixed price before the soil test?
Not honestly. A price given before a soil test and contour survey carries allowances for site works, and allowances get adjusted. Get the testing done first, then price the design that suits the ground.
Does home warranty insurance cover a cost overrun?
No. The Queensland Home Warranty Scheme covers loss of deposit, non-completion, defective work and subsidence up to the maximum amounts the QBCC publishes. It does not cover you paying more than you expected under a contract you signed.