How do I quote excavation when I don't know what's under the ground?

You price your base rate on clean soil, add provisional sums for rock and obstructions, and include a written variation clause for conditions that differ from what both parties assumed. Lodge a Before You Dig Australia (BYDA) referral first to map what is underneath before you commit to a number.

Updated 08/10/2026

Why is excavation quoting harder than most trades?

A plumber can see the pipe. An electrician can see the switchboard. An excavation contractor is pricing blind. The soil profile changes across a single block, rock shelves appear at depths nobody predicted, and underground services run in places no one documented.

The risk is asymmetric. If conditions are easier than expected, nobody thanks you and you cannot bill for time you did not use. If conditions are worse, you either absorb the loss or have a difficult conversation with a client who thought the price was fixed.

The solution is not to guess better. It is to structure your quote so the known work has a firm price and the unknown work has a clear, agreed mechanism for pricing when it appears.

What should you do before you price any excavation job?

Two things, on every job, no exceptions.

• Lodge a Before You Dig (BYDA) referral. As Safe Work Australia states in the Excavation Work Code of Practice: "Before starting any excavation work, you should always find out the location of underground services such as gas pipes, water pipes, sewer pipes, telecommunications cables and electrical cables." Call 1100 or lodge online at byda.com.au. The utility plans are free, they arrive within two business days, and they tell you where gas, water, sewer, electrical, telecommunications and other services run across the site. A referral does not guarantee there are no services (private services and abandoned lines may not appear), but it shifts the liability position if you do strike something. Without a referral, your public liability insurer may decline a service-strike claim on the basis that you failed to take reasonable precautions.
• Walk the site and read the ground. Look for surface clues: inspection covers, valve boxes, pipe markers, old concrete pads, fill that looks different from the natural soil profile. Take photos. Note the slope, the access, the soil type at the surface and any rock outcrop. These observations feed directly into your quote structure.

If the job is large enough or the site history is uncertain, recommend a geotechnical report. A basic geotech investigation for a residential block typically costs between $1,500 and $4,000 depending on the number of boreholes and the lab testing required. That is a fraction of the cost of discovering rock at depth mid-dig. The client pays for it, not you, and the report gives both parties a shared baseline for what the ground contains.

How do you structure an excavation quote that covers unknowns?

Split your quote into three layers. The client sees what they are paying for and understands where the risk sits.

Layer 1: base excavation (firm price)

This is your rate for digging, loading and carting clean, non-rock soil under normal access conditions. Price it per cubic metre or as a lump sum for the scope described. Include mobilisation, site setup, any temporary fencing or barricading required by your WHS obligations, and the BYDA referral lodgement.

Layer 2: provisional sums (priced but conditional)

A provisional sum is a line item in the quote with a defined rate that only triggers if a specific condition is encountered. Common provisional sums in excavation:

• Rock excavation. Price per cubic metre or per hour of rock breaking (hydraulic hammer or rock saw). State the rate clearly: the client knows what rock costs before it appears.
• Service protection and relocation. An hourly rate for hand-digging around live services, plus any asset-owner attendance fees the utility requires.
• Contaminated or unstable fill. A rate for separating, testing and disposing of fill that cannot go to a standard tip. Disposal of contaminated soil at a licensed facility in metro Sydney or Melbourne typically runs between $120 and $350 per tonne depending on the contamination classification.
• Additional carting. A per-load or per-tonne rate for spoil volumes that exceed the estimate, covering tip fees and transport.

Provisional sums protect both parties. The client is not paying for rock that may not be there, and you are not absorbing the cost of rock that is.

Layer 3: the variation clause (the safety net)

Even with provisional sums, conditions can differ from what both parties assumed. A written variation clause in your quote says:

• What triggers it. Conditions materially different from those described in the BYDA plans and the geotech report (if one exists), or from the assumptions stated in the quote.
• What the rate is. Your hourly rate for the machine and operator, plus any additional disposal or specialist subcontractor costs at agreed rates.
• That work pauses until the variation is approved. This is the critical line. Without it, you are working at risk and the argument about who pays happens after the money is spent.

Put the variation clause on the face of the quote, not in fine print. A client who understands the clause upfront rarely pushes back when it triggers.

What does a typical excavation quote look like with unknowns priced in?

Below is a worked example for a residential house pad on a suburban block with no geotech report and a BYDA referral showing gas and water services crossing the site. All figures are estimates for illustration only.

The range in the estimated total reflects that rock volume and service-protection hours are unknown until the work starts. The client sees a firm base price and a clear upper range, and both parties know the variation clause governs anything beyond that range.

How do you handle rock in an excavation quote?

Rock is the single biggest variable in excavation pricing. A block that looks like clean clay at the surface can hit sandstone, basalt or shale at 300 mm.

• Price rock separately, always. Never absorb rock into your base rate. If rock does not appear, the client saves money. If it does, you are covered.
• State the method and the rate. Hydraulic hammer, rock saw, chemical splitting, or drill-and-blast each carry different costs, different noise and vibration profiles, and different council and WHS requirements. Name the method in the quote so there is no argument about what was included.
• Define what counts as rock. Use plain language: material that cannot be removed with the bucket of the machine specified in the quote without the use of a rock breaker or saw. This stops disputes about hard clay, cemented fill or weathered rock.

If the site is in a known rock area (parts of the Sydney basin, the Adelaide Hills, much of Tasmania, coastal Queensland basalt), tell the client upfront that rock is likely and the provisional sum will almost certainly trigger. Transparency builds trust and avoids the phone call nobody wants mid-dig.

What about underground services you did not expect?

A BYDA referral maps most registered services, but it does not cover:

• Private services. A sewer lateral from the house to the main, a private stormwater line, or an irrigation system installed by a previous owner may not appear on any plan.
• Abandoned services. Old gas lines, decommissioned water mains and disused telecommunications cables can sit unmarked and still carry residual pressure or live current.
• Inaccurate plans. Asset-owner plans carry a stated accuracy tolerance, typically plus or minus 500 mm horizontally. A service shown 1.2 metres from the trench line could be 700 mm away.

Your quote should include a line for hand-digging or vacuum excavation (potholing) around any service shown within the excavation zone. Potholing with a vacuum truck typically costs between $250 and $500 per pothole in metro areas, and it gives both parties a verified position before the machine goes in. That cost belongs in the quote as a line item, not hidden in your margin.

If a service is struck despite reasonable precautions, the variation clause governs the cost of the delay, the repair and any reinstatement. Without the clause, you are arguing about liability after the fact.

How do you price contaminated or unknown fill?

Urban infill sites, former industrial land and any block with a history of demolition can contain fill that is not clean soil. Asbestos-containing material (ACM), hydrocarbon contamination and mixed demolition waste all require different handling, disposal and sometimes a licensed assessor before the material can leave the site.

• State your assumption in the quote. "This quote assumes clean, uncontaminated natural soil. If contaminated or hazardous material is encountered, work will stop and the variation clause applies."
• Price the known disposal rate. General solid waste (clean fill with minor concrete or brick) typically costs $50 to $90 per tonne at a licensed facility in metro areas, while contaminated soil classified as restricted solid waste can run $120 to $350 per tonne.
• Do not handle asbestos yourself. If suspected ACM is encountered, stop work, isolate the area, and engage a licensed asbestos assessor. The cost of assessment and removal is a variation, not something you absorb or price speculatively.

For a deeper look at the licensing and WHS obligations that apply to excavation, including state-by-state thresholds and SWMS requirements, see our excavation licences and permits guide.

Should you recommend a geotech report to the client?

Yes, whenever the site history is uncertain, the soil type is variable, or the job value is large enough that a rock encounter would materially change the price.

A basic geotechnical investigation for a standard residential block (two to four boreholes, lab classification of soil samples, a short report) typically costs between $1,500 and $4,000. Compare that with the cost of discovering Class 2 rock at 600 mm across a 120 m² house pad, which could add $5,000 to $15,000 or more depending on the volume and the method.

The geotech report benefits both parties:

• For you: it replaces assumptions with data. Your provisional sums become tighter, your quote is more competitive, and the variation clause triggers less often.
• For the client: it reduces surprise costs. A geotech report that says "no rock expected to 2.0 m" means the provisional sum for rock is unlikely to trigger, and the client can budget with more confidence.

Frame it as risk reduction, not an upsell. The client who pays $2,500 for a geotech and avoids a $10,000 rock variation is ahead, and they remember who recommended it.

What goes wrong when you quote excavation as a lump sum?

A single lump-sum price for excavation on a site with unknowns forces you to do one of two things, and both are bad.

• You pad the price to cover every possible scenario. The quote looks expensive compared to a competitor who priced clean soil only. You lose the job to someone who will either cut corners or have the difficult conversation with the client mid-dig.
• You price it tight and hope for the best. If rock or services appear, you absorb the loss or try to negotiate a variation after the client thought the price was fixed. Both damage the relationship and your margin.

The layered approach (base price, provisional sums, variation clause) avoids both traps. It is transparent, it is fair, and it is how the larger civil contractors have priced for decades. There is no reason a residential or small commercial excavation contractor cannot do the same.

For general quoting strategies that apply across all trades, see our tradie quoting tips guide. If speed is the problem, not structure, our guide to quoting jobs faster covers the workflow side.

How do you communicate the quote to the client?

The structure only works if the client understands it. Most homeowners have never seen a provisional sum before. Two things help.

• Walk them through it on site. Stand at the dig area, point at the BYDA markers, explain what is underneath and what could change the price. A five-minute conversation on site is worth more than a page of fine print.
• Use plain language in the quote document. Instead of "Provisional sum for Class 2 rock excavation per AS1726", write "Rock breaking: if we hit rock that cannot be dug with the excavator bucket, the rate is $280 per hour for the rock breaker. We will stop and call you before starting."

Clients who understand the quote upfront almost never dispute a variation when it triggers. The disputes come from surprises, and surprises come from quotes that hid the risk instead of naming it.