What are site costs on a new build in QLD?

Site costs are the single biggest reason a build finishes over budget, and the least understood line in a building quote. They are also the one item where the number you are shown at quote stage is almost never the number you end up paying.

This explains what they cover, why the figure moves, and how to tell whether the allowance in front of you is realistic or optimistic.

What site costs actually cover

Site costs are everything needed to make your block buildable and to connect the house to services. They are separate from the cost of the house. Broadly:

• Earthworks — excavation, cut and fill, levelling the building platform
• Retaining — where fall or cut requires structural support, including engineering and drainage behind the wall
• The slab — engineered to the soil classification, which is why the classification matters so much
• Piering — where the ground needs to be reached deeper for stable founding
• Service connections — water, sewer, stormwater, power and communications, including the distance from the connection point to the house
• Site establishment — temporary fencing, site toilet, access, erosion and sediment control, and waste removal

Why the number moves

Most advertised prices carry a site cost allowance, not a site cost. An allowance is an estimate made before anyone has tested your block, and it rests on assumptions:

• That the soil classification is at the favourable end
• That fall across the building envelope is minimal
• That no retaining is needed
• That machinery can get onto the block easily
• That service connections are close by

Every one of those is testable, and none of them is tested at the point the number is quoted. When a soil test and contour survey are done, the allowance is replaced by an actual cost, and the difference falls to the owner. The gap is regularly tens of thousands of dollars.

Soil classification, and why it drives the slab

A geotechnical soil test classifies your block according to how much the ground moves with changes in moisture. Classifications run from stable sand and rock through to highly reactive clay, and each step up requires a more heavily engineered slab.

Reactive clay is common across much of South-East Queensland, particularly through the western corridor. It expands when wet and contracts when dry, and a slab that does not account for it will crack. The engineering response — deeper beams, more steel, sometimes piering — costs money, and there is no way around it.

This is why a soil test is not a formality. It is the piece of information that turns an estimate into a price, and it is worth having before you are contractually committed rather than after.

Fall, retaining and the cost of a slope

Fall is the drop in ground level across your block. A small fall is manageable and common. Beyond that, the options are to cut into the slope, build up, split the floor level, or some combination — and each carries cost.

Retaining walls in particular are frequently underestimated. A retaining wall is not just the wall: it is engineering, footings, drainage behind it, and often a fence on top of it. On a block with meaningful fall, retaining can be one of the largest single items in the whole build.

Fall also has a knock-on effect on driveways, on where the house can sit within the envelope, and on stormwater, which has to go somewhere legal.

Access, services and the things nobody photographs

Two blocks with identical soil and identical fall can still differ:

• Access. A narrow frontage, an established tree, or a neighbouring house already built can restrict machine access and push work toward smaller, slower and more expensive equipment.
• Service distance. The further the house sits from the connection point, the more trenching and conduit. On larger or irregular lots this adds up quickly.
• Existing structures or vegetation. Removal, and sometimes approval to remove, before anything can start.
• Overlays. Flood, bushfire, character or vegetation overlays can impose construction requirements that are entirely separate from your design choices.

How to test the allowance you have been given

You cannot make a site cost allowance accurate by asking for one. You can, though, find out how much confidence to place in it:

• Ask what soil classification the allowance assumes, and what happens at the next classification up
• Ask what fall it assumes across the building envelope
• Ask whether retaining is included, excluded or assumed to be nil
• Ask what the allowance covers for service connections, and over what distance
• Ask, plainly, whether it is capped — and if it is, what the cap excludes

A builder who answers those precisely is telling you they have priced your block. A builder who answers them vaguely is telling you they have priced an average block, and you will find out the difference at slab stage.

Getting a real number before you commit

The sequence that avoids most of this pain:

• Get a soil test and contour survey on the actual block, as early as you can
• Have every builder quote against those documents rather than against assumptions
• Require site costs to be broken out as a separate schedule, not folded into a single figure
• Hold a contingency anyway — ground is the one part of a build nobody can see until they open it

Site costs are not a trap set by builders. They are genuine, unavoidable, and hard to know in advance. The problem is not that they exist — it is that they are routinely presented as though they are already settled when they are not.