TL;DR: Site costs and preliminaries pay for everything that happens before and around the house: getting the block ready, connecting services, and keeping the job site safe, legal and clean for the whole build. Most of these costs depend on the block rather than the plans, so they are the part of a residential quote most likely to be underpriced. Before you price, get a soil report, a feature and level survey, the council's legal point of discharge and the service authority information. Put rock and other latent conditions in the contract as a stated rate, list every prelim as its own line, and price hire items off a realistic program rather than a hopeful one.

Ask a builder where a fixed-price house lost its money and the answer is rarely the frame or the kitchen. It's usually something that happened before the slab, or something that sat on site for the whole job. Site costs building a house cover the earthworks, rock, service connections, scaffold, temporary fencing, toilets, power and waste, plus the time it takes to manage all of it. These costs change with every block. Two identical floor plans on two different lots can carry very different site costs, and the plans won't tell you which kind of lot you're quoting.

This guide goes through each line item: what drives the cost, what to check before you price it, and how to word it so a surprise in the ground doesn't come straight out of your margin. Owner builders, this is the list that usually goes missing from the spreadsheet.

A note on numbers. We don't print dollar figures in this guide. Rates for excavation, scaffold hire, skips and authority fees vary by state, council, supplier and season, so any figure we gave would be wrong for most readers. Get current local quotes for every item below.

What counts as preliminaries and what counts as site costs

The two get mixed up, and that's often how an item ends up missing from the quote.

Preliminaries (prelims) are the costs of running the job that don't belong to any one trade:

• Site establishment and supervision
• Contract works and public liability insurance
• Permits, set-out survey and council fees
• Temporary fencing, site toilet, temporary power and water
• Scaffold and edge protection
• Waste removal, skips and cleaning, including the final clean

Site costs belong to the block itself:

• Site cut, fill and retaining
• Rock removal
• Extra footing depth or piers where the soil needs them
• Site drainage and stormwater
• Service connections and trenching
• Driveway crossover, tree protection and sediment control

Some builders quote a base price and list site costs separately. Others roll everything into one number. Either way works, as long as every item appears somewhere on the page. The one that causes trouble is the item that appears nowhere.

Why site costs building a house blow out more than any other line

There are three reasons, and they compound.

They rely on information you may not have at quote time. The soil class, rock, the fall across the block, where the sewer connection sits, whether power arrives overhead or underground. Get any of these wrong and accurate house pricing won't save the job.

Many of them are charged by time. Scaffold, fencing, site toilets and some skip arrangements are hired by the week or by the hire period, so check how each of your suppliers charges. A job that runs six weeks over pays six extra weeks of hire on every one of them, on top of the extra supervision.

They aren't on the drawings. Nobody draws a site toilet. If your quoting process starts from the plans and works through the trades, prelims only get counted when someone remembers them.

The soil report is where the first surprises show up. AS 2870 classifies residential sites as A, S, M, H1, H2, E or P depending on how reactive the soil is, and a P (problem) site needs an engineered design. A more reactive class means a stiffer slab and deeper or more footings, which means concrete and steel that weren't in the last job you priced. Price footings and piers from the engineer's design for this block, not from memory. Our concrete calculator is handy for sense-checking volumes when the engineer adds piers.

Site cut, fill and retaining

A house on a sloping block needs a level platform. The excavator cuts the high side, and the spoil either fills the low side or leaves site on a truck. What drives the cost:

• The fall across the building footprint. Read it off the feature and level survey, not by eye at the site inspection.
• Machine access. Narrow side access, overhead power lines, neighbouring footings close to the boundary and a steep driveway all slow a machine down or call for a smaller one.
• Where the spoil goes. Spoil that can stay on site is far cheaper than spoil that has to be carted away. Spoil that needs testing before a tip will accept it adds cost and time again.
• Retaining walls. If the batter from the cut or fill won't fit inside the boundary, you'll need a wall, and walls above a certain height need engineering and may need a permit. That height varies by state and council, so ask your building surveyor rather than assuming.
• Drainage behind the wall. Ag pipe, aggregate and a connection to the stormwater system, all of it easy to leave out.
• Sediment control. Council conditions often require silt fencing and a stabilised entry, and both have to stay maintained for the whole job.

Ask your excavation contractor whether they're pricing per hour or per cubic metre, and exactly what their cartage price includes. If you calculate the cut and fill volume from the survey yourself, you can check their number instead of just accepting it.

Before any machine breaks ground, lodge an enquiry with Before You Dig Australia for the underground asset locations. It's free, and hitting a service costs far more than the time the enquiry takes. For trench and excavation safety, Safe Work Australia's model Code of Practice for excavation work sets out the controls expected on a job site, including for trench collapse.

Rock: the line item nobody can see

Rock is the classic latent condition. Soil report bores sample a few points, not the whole block. You might hit floaters that a bigger bucket can lift out, or you might hit bedrock that needs a rock breaker, a larger machine, more days and heavier cartage. Rock can also force the footing design to change, which puts the engineer back on the job.

Don't absorb rock into a fixed price unless you have very good reason to believe there isn't any. You have two common options:

1. Exclude rock and price it as a variation at a stated rate, such as per hour of rock breaker or per cubic metre removed and carted.
2. Include a provisional sum for rock, with the rate shown so the client can see how it will be adjusted.

Either way, make the trigger objective. Define what counts as rock, for example material the nominated machine can't remove with a standard bucket. When you hit it, photograph it, record the hours and the volume each day, and get the client's sign-off while the excavator is still on site, not at the next progress claim.

Read the latent conditions clause in whichever contract you use. Each state's domestic building law also has its own rules on provisional sums and variations. If you build in Victoria, our guide to home warranty insurance in Victoria explains how domestic building insurance changes your quoting and job admin.

Service connections: water, sewer, stormwater, power and NBN

Each service has its own authority, its own fee and its own lead time. Price the whole run from the connection point to the house, not just the connection. A house set back 30 metres from the street needs 30-odd metres of trenching for every service that comes in from the front.

• Water. A new tapping or meter is done by the water authority, which sets the fees and the timing.
• Sewer. Find out where the property connection point is. If the house sits lower than it, you may need a pump. Get the authority's asset information or the property sewerage plan before you quote.
• Stormwater. Council nominates the legal point of discharge. On a block that falls away from it, you could need a pump, a charged system or an easement through a neighbour's land. Ask for the legal point of discharge in writing before you price.
• Power. The distributor connects the supply, and whether it arrives overhead or underground changes the work involved. The electrician prices consumer mains by length from the point of supply to the meter box.
• NBN and telecommunications. Pit and pipe for new developments needs ordering early, because it's easy to forget until the client asks why the internet isn't on.

If an authority's fee hasn't been confirmed when you quote, show it as a provisional sum and say where the figure came from.

Scaffold and edge protection

On two storeys, a steep roof or any work at height, scaffold and edge protection are both a WHS obligation and a real cost. Under the model WHS Regulations, scaffolding work where a person or thing could fall more than 4 metres needs a high risk work licence, and scaffolds are expected to meet the AS/NZS 1576 series. Single-storey jobs often still need roof edge protection, so check with your roofer before leaving it off.

What drives the cost:

• Perimeter and height, and the number of lifts
• Hire duration, which is where most of the blowout happens
• Mid-job changes, such as moving or adjusting it for brickwork, cladding or roofing
• Access problems that make erecting and dismantling slower
• Inspections required under the WHS Regulations for the scaffold you're using

Duration is the part you control. Build the scaffold into the program, sequence the roofer, bricklayer and cladder so they work off it back to back, and get it down as soon as the last trade is done. A wet month with scaffold standing and nobody on it costs money every week.

Temporary fencing, site toilet, power and council permits

These are the items owner builders forget most often, and builders get them wrong when they price them from the last job instead of this one.

• Temporary fencing. Securing the site is usually a council condition as well as a WHS duty. AS 4687 covers temporary fencing and hoardings. Hire is often per panel per period, plus delivery and collection. Shade cloth catches wind, so allow for extra bracing and ballast on exposed sites.
• Site toilet. Workers must have access to toilets. Price the hire and the servicing for the full program.
• Temporary power. A builder's pole or temporary supply needs a licensed electrician to install it and the distributor to connect it. Order it early, because lead times can hold up the start.
• Temporary water. A standpipe or metered connection for the trades.
• Council asset protection. Many councils charge an asset protection fee or hold a bond, and inspect the footpath, kerb and nature strip before and after the job. A cracked kerb from a concrete truck can come out of that bond.
• Crossover and footpath permits. A vehicle crossing permit and any permit to occupy the footpath or road for deliveries, skips or a crane.

If the block is in a bushfire-prone area, the BAL assessment is also a site cost, and it can change the construction spec for the whole house. Our guide to BAL rating requirements explains what each level means for the build.

Waste, skips and the final clean

Waste looks small on each invoice and adds up across a job. Skips are usually priced by bin size and per lift, and mixed waste generally costs more than sorted. Landfill levies differ from state to state, so your skip supplier's rates in one state tell you little about another.

Ways to keep the waste line under control:

• Write it into subcontracts that trades take their own packaging and offcuts away, and enforce it.
• Separate clean timber, brick and concrete from mixed waste where your supplier rewards it.
• Check whether a skip on the street needs a council permit where you're working.
• Allow for concrete washout, which may need its own controls under council or EPA conditions.
• Price the builder's clean and the final clean before handover as separate lines. Window cleaning at handover is the one people forget.

On a knockdown-rebuild, demolition and asbestos come first. Under the model WHS Regulations, removing more than 10 square metres of non-friable asbestos needs a licensed removalist, and any friable asbestos needs a Class A licence. Get the asbestos survey before you quote the demolition.

How to price site costs so the number holds up

Before you price a single prelim, collect this:

1. Soil report with the AS 2870 classification, and the engineer's footing design
2. Feature and level survey showing contours, existing services, trees and neighbouring structures
3. Title and plan of subdivision for easements and covenants
4. Council's legal point of discharge and any planning or permit conditions
5. Service authority asset information and the property sewerage plan
6. BAL assessment if the site is bushfire-prone
7. An access assessment covering width, overhead lines, street parking and delivery space
8. A realistic program, because it drives every hire item

Then give each prelim its own line with a unit (per week, per cubic metre, per hire, per lift), a quantity, a rate and the GST treatment. Watch GST closely. Supplier and hire rates are often quoted ex GST, while a residential price to a homeowner must include it. Mix the two in one spreadsheet and you've underpriced those lines by 10%.

During the build, record site cost variations on the day they happen, with photos, quantities and the client's approval. Whatever you use to run jobs, it should keep that record somewhere better than your phone's camera roll. Our roundup of the best construction project management software in Australia covers what to look for.

What owner builders should budget for

As an owner builder, you are the builder, so every prelim on this list is yours to arrange, hire and pay for. Owner-builder permit rules vary by state, so check with your state regulator before you start.

There's no universal contingency figure for site costs. The right amount depends on how much you actually know about the ground. A flat block with a deep soil report and a confirmed sewer connection needs less than a sloping block where nobody has looked below the topsoil. Whatever you set aside, keep it untouched until the slab is poured. Spending it on upgrades before the earthworks are finished is how owner builders end up short at lock-up.

Frequently asked questions

What's included in site costs when building a house?
Usually the site cut and fill, retaining, rock removal, extra footing work the soil needs, drainage, service connections and trenching, and the driveway crossover. Prelims such as fencing, scaffold, toilets, temporary power and waste are often listed alongside them. Ask your builder for the full list so you can see what is included and what is provisional.

Why did my site costs go up after I signed the contract?
Usually because of a latent condition, most often rock, or because a provisional sum was adjusted to the actual cost. A well-written contract states the rate and the trigger in advance, so the increase can be checked against something you have already agreed to.

Can a builder find rock before quoting?
More soil bores and a test pit dug with an excavator reduce the risk, but they don't remove it. A bore samples a point, not a whole block. That's why rock is normally handled as a rate or a provisional sum rather than a fixed price.

Do preliminaries attract GST?
Yes. Prelims are part of the building work you supply, so a registered builder's residential price to a homeowner includes GST on them like everything else. The common mistake is entering hire rates ex GST and forgetting to add it.

How long should I allow for scaffold and fencing hire?
Allow for the full program, plus a realistic allowance for weather and trade delays. Ask each supplier about their minimum hire period and how they charge for extensions, because the extensions are where these lines blow out.

Price the block, not just the house

Prelims and site costs aren't hard to price. They're easy to forget, and they shift with every block. A soil report, a survey, the legal point of discharge and an honest program cover most of the risk. A clear rock clause covers most of what's left.

If you want the take-offs done before you're back in the ute, the free Built Simple app puts our calculators on your phone, including concrete, with no signup needed. Have a play with it on your next site inspection.