What site costs actually are

A building quote has two halves: the house, and getting the house onto your particular piece of ground. The first half is easy to compare between builders. The second is where the money moves.

What is inside the number

Soil classification. A geotechnical report classifies your ground, and the classification determines the footing system. Reactive clay needs deeper, stiffer footings than sand. This is structural, not cosmetic, and it is the biggest single driver.

Cut and fill. Levelling a sloping block means excavating on the high side, filling on the low side, and retaining the difference. Costs scale sharply with fall.

Rock. If the excavator hits rock, the price changes. Nobody knows until they dig, which is why rock is almost always a provisional allowance rather than a fixed price.

Service connections. Water, sewer, power, stormwater and telecoms from the street to the house. On an estate lot these are short and predictable. On an established block or acreage they are neither.

Access. Whether a concrete truck and a crane can get in, turn around and reach. Narrow, steep and battleaxe blocks all add cost to every trade, not just the earthworks.

Protection works. Where excavation is near a boundary you may be legally required to protect the neighbour's property, which can mean underpinning or shoring.

Why two quotes differ so much

Usually because they assume different things. One builder prices a real soil report; another uses a standard allowance for a classification your block may not have. The cheaper headline is frequently the more expensive house.

Compare the assumption, not the number. Ask every builder in writing: what soil classification is this priced on, what rock allowance is included, and what happens to my price if the report comes back worse.

What to do before you sign

Get the soil test and the contour survey done, and give the same two documents to every builder you are asking to quote. It is the only way to get numbers that mean anything against each other — and it costs a fraction of one variation.

What the two reports actually tell you

The geotechnical report gives the site classification under AS 2870, which sets the footing system. It also flags fill, groundwater and anything that would push the site into the problem-site class. See soil classification and footings.

The contour and feature survey gives levels across the block, the position of existing structures, trees, easements and the service connection points. It is what lets a builder calculate cut and fill rather than estimate it, and what reveals an easement running where you wanted the garage.

The items that surprise people

Service connections. Distance to the connection point is not uniform. A block where sewer runs past the frontage is a different proposition from one where it has to be brought a long way, or where the fall is wrong and pumping is needed.

Temporary works. Site fencing, temporary power and water, toilet, waste bins and a crossover to get vehicles off the street. Small individually, real collectively, and often assumed rather than listed.

Termite management, where applicable. A system is required in most of Australia and the method affects the slab detail.

Removing what is already there. On a knockdown rebuild: disconnections, asbestos assessment where the era suggests it, demolition, and disposal. On a vacant block: tree removal, which may itself need approval.

Where a suburb page helps

Overlays and hazard mapping are site cost drivers before they are compliance steps — a bushfire rating changes construction, a flood control can set the floor level, and an acid sulfate soil mapping can change what earthworks require. Our area pages report what is mapped in the suburb, with the source and the date read, so you know which questions apply to your block before you commission anything.