· by Rick Kosta
You have a quote in front of you with "site cut" on it, and a number beside it that is bigger than you expected. Nobody has explained what you are buying.
Here is the plain version: a site cut is the excavation that turns your sloping block into a flat, solid platform for the house to sit on. It happens before anything else, it is one of the few costs that can move significantly once work starts, and understanding it is the difference between reading your quote and guessing at it.
What a site cut actually is
Almost no block is naturally flat. Even ground that looks level to the eye usually has a fall across it, and a house needs a level base to be built on.
So the high side gets cut away. Soil is excavated down to a level that gives you a flat pad at the right height, and that pad is what the slab is poured on. That is the whole idea. Everything else is detail about how much, where it goes, and what has to be held back afterwards.
The cut is set out by a surveyor working from the builder's drawings, not chosen on the day. The finished floor level of the house determines the level of the pad, and the pad determines how deep the cut has to be.
Cut and fill, and why the difference matters
On a sloping block there are two ways to get a level platform. Cut the high side down, or build the low side up. In practice most sites do some of both, which is where the phrase "cut and fill" comes from.
Those two halves are not equal, and this is the single most useful thing to understand about your quote.
Cut is undisturbed ground. It has been sitting there compacting under its own weight for a very long time. It is as good a base as you will get.
Fill is soil that has been moved. It has to be placed in layers and compacted properly to carry load, and even done well it is engineered ground rather than natural ground. Done badly it settles, and a slab sitting partly on cut and partly on poorly compacted fill is the classic recipe for differential movement and cracking.
This is why builders often prefer a deeper cut over a shallower cut with more fill, and why "we will just fill the low side" is worth asking questions about. It is also why the fill on a properly run job gets compacted in layers and tested rather than simply pushed into place.
What determines how deep it goes
Four things, mostly:
- The fall across the block. The steeper the ground, the more has to come off the high side to reach a level pad. Depth grows quickly with slope.
- The finished floor level. Set by the builder and the design, and it fixes where the pad has to end up.
- What is under the surface. Topsoil, fill from a previous build and soft material generally cannot be built on and has to come out, so the cut may go deeper than the levels alone suggest.
- The slab and footing design. A waffle slab, a stiffened raft and a piered system do not all want the same thing underneath them.
That third one is where surprises live. Nobody can see through soil. A block that was filled by a previous owner, or that has an old slab or footings buried in it, can turn a straightforward cut into a deeper and more expensive one, and that is generally discovered on the day rather than predicted.
What happens to everything that comes out
A surprising amount, and it does not stay the size it was.
Soil swells once it is dug. Ground that measured a certain volume in place takes up meaningfully more once it has been broken up and loaded, so the number of truck loads is always higher than the raw calculation from the drawings suggests. If your quote seems to have more cartage in it than you expected, that is usually why.
Where it goes depends on what it is. Clean fill can often be reused on site or taken somewhere it is wanted. Contaminated material, material with buried rubbish through it, or spoil nobody has a use for goes to a tip and gets charged by weight. On a lot of jobs the cartage and disposal is a bigger line item than the digging.
Batters and what holds the cut back
When you cut into a slope you create a face, and that face will not stand vertically in most soils. It has to be dealt with one of two ways.
A batter is the simple option: the cut face is left sloped back at an angle the soil will hold. It costs nothing beyond the extra excavation, but it eats space, and on a narrow block there is often not enough room for one.
A retaining wall holds the face vertically and gives you the space back. It costs more and it needs proper drainage behind it, but on a tight site it is frequently the only option.
Which one your job needs is a design question that should be settled before the cut, not after, because the answer changes where the cut goes and how deep it is. It is also a genuine fork in the cost of the project.
Who is responsible for what
This trips people up, particularly owner-builders.
The builder or designer sets the finished floor level and the position of the house, specifies the slab and footings, and is responsible for the design the cut is executed to. The surveyor sets out the levels and pegs on the ground. The excavation contractor cuts to those levels, manages the spoil and leaves a platform to the specified tolerance.
The place it gets blurry is when something unexpected comes out of the ground. Rock, old footings and buried fill are usually handled as a variation, because they cannot be priced honestly in advance. What separates a good arrangement from a bad one is whether that possibility was discussed at quote stage or raised for the first time when the machine hits something.
It is a fair question to ask before you sign: what happens if there is rock, and how is that priced.
Reading the site cut line on your quote
A single figure with "site cut" beside it is not much to go on. A quote you can actually assess separates out the parts that behave differently, because they are the parts that move.
Things worth seeing itemised, or at least explained:
- Excavation, usually by volume or by hours, and to what level
- Cartage and disposal, separately from the digging, because it is often the larger number and it depends on where the material can go
- Fill, if any is being placed, including whether it is being compacted in layers and whether compaction testing is included
- Batters or retaining, and which of the two the price assumes
- What happens if rock or buried material turns up, and how that is priced
- What is excluded, which is often where the surprises hide
You are not looking for the cheapest number. You are looking for the quote whose assumptions you can see, because a low price that assumes clean soil, easy access and somewhere free to tip is not really a low price. It is the same job with the risky parts left out of the total.
If two quotes are far apart, the gap is almost always in cartage, in fill treatment, or in what has been assumed about the ground. Ask about those three and the difference usually explains itself.
What a good site cut leaves behind
A level pad at the specified level, within tolerance, with the fill placed in layers and compacted rather than pushed. Batters or retained faces dealt with as designed. Spoil gone. Drainage considered, because water that runs onto a fresh pad and sits there is a problem the next trade inherits. Access still usable for whoever comes next.
It is not glamorous work and it is invisible within a fortnight of the slab going down. It is also the layer everything above it depends on, and the hardest thing on the whole project to go back and fix.
If you have a quote in front of you and want a second opinion on the site cut in it, or you want yours priced, have a look at our excavation and earthmoving services or send through the plans and we will take a look.
Ready to act on this? Explore our excavation and earthmoving services, or learn more about plant and machinery hire.
