Shea CullenNSW Registered Architect 9748 · Updated 23 August 2026Every cost article I have written, including my own one on Central Coast build rates, deals in ranges. Per square metre figures, published guides, indicative allowances. They are useful for setting expectations, but they do not tell you what will actually leave your account.
A client of mine has kept a spreadsheet of every payment she has made on her new house since the first architect invoice in April 2024, and she has agreed to let me publish it. These are the invoices, in order, with dates.
I have removed her name and the address, and the consultants and trades are described by their trade rather than named. The one exception is the builder, who is named. The numbers are exactly as she recorded them.
What the house is
A new 155m² single storey home on the Central Coast, built by an owner builder using prefabricated straw bale wall panels, on a slab supported by steel screw piers.
Design started in April 2024 and the development application was lodged in January 2025. By early 2026 the project was no longer inside budget, because construction costs had risen through the approval period, so the design was revised and lodged again as a section 4.55 modification, approved in March 2026. The construction certificate was lodged in April 2026, earthworks began in June 2026 and the slab was poured in August 2026.
The headline numbers
As at 22 August 2026:
- Design, approvals and fees: $50,929.70
- Construction paid to date: $334,185.50
- Total spent so far: $385,115.20
- Still to pay to reach lockup: $256,451.69
- Total known cost to lockup: $641,566.89
Across 155m², that works out at:
- $4,139.14 per m² for everything known so far, fees included
- $3,810.56 per m² for construction alone
That last figure is the cost of getting to lockup. It excludes external cladding, which is not yet priced. It also excludes everything that happens after lockup: kitchen, bathrooms, internal linings and fitout, floor coverings, electrical and plumbing fitout, painting, driveway, landscaping and retaining. It is not the price of a finished house, and the per square metre rates will rise before it is.
For context, the rates I usually see on the Central Coast are around $3,500 to $4,500 per m² for project and volume homes and $6,000 to $7,500 per m² for architect designed homes. This house is tracking below the architect designed range, with the fitout still to come.
Design, approvals and fees: $50,929.70
Most of this was spent well before the first excavator arrived.
- Architect: $17,999.99. That is us, across concept design, the development application and the construction certificate drawings, paid in progressive instalments from April 2024 to May 2026.
- Owner builder insurance: $9,820.00, recorded as two payments of $4,910.00
- Private certifier, construction certificate: $3,610.00
- Stormwater engineer: $3,041.50, which covers $2,200.00 for the draft plan and $841.50 to finalise the report after the house was resized
- Structural engineer: $2,750.00, which covers $1,870.00 initially and $880.00 for an updated stormwater management plan
- Town planner, statement of environmental effects: $2,300.00, including $300.00 to revise it for the section 4.55 modification
- Surveyor, updated survey of the lot: $1,155.00
- Energy assessor, NatHERS and BASIX certificates: $1,078.00
- Council fees: $4,266.21, made up of $2,818.96 for the development application, $865.06 for the section 4.55 modification, $536.19 to inspect stormwater and toilet connections, and $46.00 in application fees
- NSW Government charges: $2,025.00, made up of $1,700.00 Long Service Levy, $233.00 owner builder permit and two lodgement fees of $46.00
- Owner builder course and book: $244.00
- Estate construction bond: $1,000.00
- Site container hire: $1,500.00
- Tiles: $140.00
Why this is the cheapest money in the project
$50,929.70 looks like a large number on its own. Set against $590,637.19 of construction, it is 8.6 per cent.
The drawings, the engineering and the approvals are where the house is decided. Every square metre you build, every pier under the slab, every window opening and every compliance requirement is settled in that 8.6 per cent, and then paid for at full price in the other 91.4 per cent. A design that saves ten square metres of floor area saves roughly $38,000 of construction on this build. A design that gets the structure wrong costs far more than that to fix once it is in the ground.
What the section 4.55 cost
Changing an approved DA is not free. When the project fell outside budget and the design had to be reduced, the modification cost $865.06 in Council fees and $300.00 to the planner, and the stormwater plan was updated for $880.00.
Construction to date: $334,185.50
- Builder, straw bale panels and slab: $248,454.70
- Windows and external doors: $73,823.90
- Earthworks, cut and dispose of fill: $6,615.00
- Truck and levelling for set out: $2,550.00
- Excavator hire: $2,080.50 across three separate hires
- Estate plant hire, truck and tractor to clear the site: $512.50
- Hardware, pegs and screws for setting out: $148.90
How much do prefabricated straw bale panels cost?
The straw bale wall panels came to $90,874.78 supplied and installed, which is $586.29 per m² of floor area:
- Panel deposit, February 2026, paid in four parts: $36,477.29
- Increase in deposit after upgrading the panels to be rendered internally: $4,449.60
- Final payment for panels, April 2026: $36,477.29
- Delivery, crane, truck driver, labour and installation: $13,470.60
That is 15.4 per cent of the construction cost to lockup. External cladding sits on top of it and has not yet been priced, so treat $90,874.78 as the walls, not the weatherproof envelope.
The walls were delivered and stood up in one day. Everything had been measured and made to fit, and there were no mistakes on site. We were very impressed with Viva Homes.
The slab was 44 per cent of it
The slab, taken as a whole, came to $147,734.38, or $953.13 per m²:
- Deposit: $21,727.41
- Screw piering complete: $14,484.94
- Formwork and drainage complete: $28,969.88
- Variation, ten extra screw piers and earthworks for water tanks: $2,885.00
- Slab pour, paid in four parts: $79,667.15
It was quoted at $144,849.38 including piering, plumbing under the slab and termite treatment, and it landed at quote plus that single $2,885.00 variation. Screw piers were chosen to bring the slab cost down. It is still the largest single element of the build so far.
Windows were 22 per cent of it
$73,823.90 for double glazed windows and external doors in uPVC frames, which is $476.28 per m². It was paid as an exact fifty fifty split: $36,911.95 as deposit in March 2026 and $36,911.95 on completion in June 2026.
That is almost as much as the slab pour itself, and more than four times the architect's fee. On a house designed to perform, glazing needs to be priced before the design is locked.
The rest of the builder's payments
- Initial quote for the house, June 2025: $2,750.00
- April 2026: $1,365.65
- Window sills in crafted hardwood: $4,625.89
- Excavator hire for sixteen hours to move soil for concrete piers and paths: $1,104.00
Note the pattern in those part payments through the whole record: twenty thousand, then ten thousand, then the remainder. That is a client working around daily bank transfer limits, three transactions to make one payment.
Still to pay to reach lockup: $256,451.69
These are the scheduled progress payments, with the builder's expected dates:
- Panels installed, 20 August 2026: $13,470.00
- Deposit for the balance to lockup, 24 August 2026: $22,438.87
- Wall and ceiling frames installed, 2 September 2026: $33,658.30
- Main roof installed, 8 September 2026: $56,097.17
- Windows installed, 16 September 2026: $67,316.61
- Internal render complete, 29 October 2026: $22,438.87
- Final, 12 November 2026: $22,438.87
- Verandahs: $18,593.00
Roughly $180,000 of that falls in the three weeks between 24 August and 16 September. If you are financing a build, the drawdown schedule matters as much as the total.
What this tells you
Approval time costs money on a rising market. The house was approved, then had to be redesigned and lodged again because construction costs had moved past the budget during the approval period. Twenty six months passed between the first architect payment and the first excavator. That is normal rather than unusual, and it needs to be in the plan.
Lockup is not a finished house. $641,566.89 buys a sealed shell with no kitchen, no bathrooms, no floors, no paint, no driveway and no landscaping. Anyone comparing this to an advertised project home price needs to compare it to that builder's finished, on your block, turnkey figure, which is the point I make in why the advertised base price is not your price.
Owner building saved less than people assume. The permit and course together were $477.00 and the insurance was $4,910.00 a policy. What owner building bought here was control, and what it costs is that the work cannot be covered by home warranty insurance and must be disclosed for seven and a half years on sale. I have set out that trade in full in the guide for owner builders.
Variations happen even on a well run job. Two on this build so far: $2,885.00 for extra screw piers and $4,449.60 to upgrade the panels. Both were modest, and both followed from understanding the ground and the finishes properly.
What I would do with this
Write the four numbers down before you commit to anything: fees, construction to lockup, fitout to completion, and site works. Most people can estimate the second. The first and the fourth are the ones that get missed.
My thanks to the owner for keeping this record and for letting me share it. She is still building, and I will update these figures as the house is finished.
If you want a reality check on what your own block is likely to cost, including the site costs people forget, book a free 15 minute chat and we can go through it. The rest of the journey is mapped in before you build on the Central Coast.