Budgeting guide
A concept budget template: give a range before the full quote
Clients ask what something will roughly cost long before you can measure it and give a fixed price. A concept budget answers that honestly: a range, the assumptions behind it, and the allowances that firm up later. Done as a range it builds trust and qualifies the job. Done as one number, it sets up an argument the day the real quote lands higher.
Why a range, not a number
At concept stage you have a sketch, a site visit and a rough scope, not a measured set of drawings. The honest output is a range, because the cost genuinely depends on choices the client has not made: the finish level, whether the slab needs a pier and beam, how the kitchen is specified. A single figure reads as a promise, and the client anchors to it. A range with a most-likely point reads as what it is: an early estimate, not a quote.
The range, drawn
A single-storey rear extension, roughly 45m². The band runs from a lean build to a high-finish one; the marker is the most likely figure on the assumptions below. Illustrative, not a price.
Concept budget · rear extension, 45m² · ex GST
Assumes: single storey, no rock excavation, standard ceiling heights, mid-range finishes, services within reach. Excludes: landscaping, council and certifier fees, furniture.
The template, by element
Break the range down so the client sees where the money sits and which lines are allowances. The same template carries to the measured quote later, so nothing is reinvented.
Concept budget
Rear extension, 8 Banksia Cl
Indicative only · not a fixed-price quote
| Element | Low | Most likely | High |
|---|---|---|---|
| Demolition and site prep | $8,000 | $11,000 | $15,000 |
| Substructure and slab | $34,000 | $41,000 | $52,000 |
| Structure and framing | $45,000 | $55,000 | $70,000 |
| Roof, cladding and windows | $38,000 | $46,000 | $58,000 |
| Services plumbing, electrical, HVAC rough-in | $32,000 | $38,000 | $47,000 |
| Fit-out kitchen, joinery; tapware and tiles are PC items PC items | $25,000 | $34,000 | $45,000 |
| Site works adjusts to actual cost Provisional sum | $8,000 | $11,000 | $15,000 |
| Indicative total, ex GST | $248,000 | $292,000 | $355,000 |
Assumptions carry the number
Most budget blow-out arguments are really assumption arguments. The client remembers $248,000 and forgets it assumed a lean spec and an easy site. Put the assumptions and exclusions next to the range, in the client's words, and make them the thing the next conversation is about. When the brief changes (a steeper site, a stone kitchen), you move the marker and point at the assumption that changed, rather than defending a number that was never wrong.
- State the spec level the range assumes: lean, mid, or premium finishes.
- Name the site assumptions: no rock, services within reach, normal access.
- List what is out: landscaping, fees, furniture, anything the client might assume in.
- Flag PC items and provisional sums as allowances, not fixed costs.
A concept budget is not a fixed-price quote, and it pays to say so in those words. It is an estimate, so the figure can move; the client carries that movement, not you. Name the next step (a measured quote off drawings) and what it costs if you charge for it.
From concept to contract
The concept budget is the first of three documents on the same job. Each one narrows the number.
Concept budget
A range off a site visit and a rough scope. Qualifies the job and the client's budget before anyone pays for drawings.
Measured quote
A fixed price off measured drawings, with PC items and provisional sums set. The range becomes one figure plus allowances.
Building contract
A HIA or Master Builders form: progress claims, retention, defects liability and practical completion. The quote becomes the contract sum.
Build the budget on real rates
Proposr's concept budgeting starts from an Australian rate library, holds the low, likely and high columns, and carries the same template to the measured quote. The client reads the range, the assumptions and the allowances on one branded page.
Sources
General information for Australian builders, not legal or cost advice. The figures and ranges are illustrative and vary widely by region, site, spec and the day's prices; build your own from current rates and confirm contract requirements with your state building authority.