What it actually costs to build a house

Search this question and you will find confident numbers. They are averages of dissimilar houses on dissimilar land, and applying one to your block is how budgets get set two hundred thousand dollars wrong.

What is useful is knowing what moves the number, so that when you do get quotes you can tell whether they are comparable.

The land does more than the house

Soil classification. A reactive clay site needs a different footing system to sand, and the difference is structural, not cosmetic. Most base prices assume a middling classification; if the soil report comes back worse, site costs rise.

Fall across the block. Cut and fill, retaining and drainage scale quickly with slope. A block with two metres of fall is a materially different build to a flat one, with the same house on top.

Access. Can a concrete truck and a crane get in? On an established street, or a battleaxe, or a steep site, sometimes not — and the workaround costs money on every trade.

Overlays. A bushfire rating drives construction requirements. A heritage or character control drives design and approval time. A flood overlay can drive the floor level. These are the difference between two identical-looking blocks.

The specification does the rest

Base specifications exist to produce an advertised price. The gap between a base specification and what most people actually want — in the kitchen, in the glazing, in the floor coverings, in the landscaping — is where the quote moves after you sign. Ask for the upgrade schedule priced before you commit.

What is usually excluded

Site costs beyond an assumed allowance, driveway, landscaping, fencing, window furnishings, letterbox, clothesline, and on a knockdown rebuild the demolition itself. None of these are optional in practice; all of them are frequently outside the headline number.

How to get a number you can rely on

Three comparable quotes, from builders who have seen your soil report and your contour survey, priced against the same specification. That is the only number worth budgeting against, and it is the thing we exist to get you.

Why per-square-metre figures mislead

The rate is an output, not an input. It is calculated after a job is priced, by dividing a total by a floor area, and it carries every assumption of that particular job — the site, the specification, the shape of the building, the year. Applied forward to a different house on a different block it reproduces none of those assumptions.

It also scales badly. A smaller house does not cost proportionally less, because the expensive rooms do not shrink: a kitchen and two bathrooms cost roughly what they cost whether the house around them is large or small. Rate-per-square-metre flatters big simple houses and penalises small complex ones.

Shape costs more than size

Two houses of identical floor area can differ substantially in price because of articulation. Every corner is extra framing, extra cladding, extra flashing and extra labour. A simple rectangular plan under a simple roof is the cheapest way to enclose a given area, and each step away from that — a wing, a gable, a change in roof pitch, a cantilever — adds cost that floor area does not capture.

The same is true vertically. A second storey saves on footings and roof per square metre but adds a stair, structural upgrades and often a second bathroom. Whether it is cheaper depends on the block, not on a rule.

The costs that sit outside the build contract

Budgets are commonly set on the build price alone. Also real: design and documentation, engineering, soil testing and survey, council and certifier fees, service connections, finance costs during construction, insurance, and rent or a mortgage on somewhere else to live while it happens. None of these are in a builder's quote and all of them are in your project.

Contingency

Hold one, keep it separate from the build budget, and size it to how much of your scope is still an allowance rather than a price. A contract heavy with provisional sums needs a larger contingency than one where the site costs are fixed against an actual soil classification — see provisional sums and prime cost items. A contingency you have already spent on upgrades is not a contingency.