Ordering a soil report: cost, timing, and how to read the site class
When to order a soil report, who does it, what it costs (about $500 to $1,200 ex-GST for a standard block), and how to action the AS 2870 site class on your job.
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A soil report (geotech report) classifies your block under AS 2870 so the engineer can design the slab and footings to suit the ground. For a standard residential block expect roughly $500 to $1,200 ex-GST, more for large, sloping, or hard-to-access sites. Order it early, before you firm up a slab quote and before lodging in reactive-soil areas, because the site class (A through P) drives the slab cost and most certifiers and lenders want the report before a Construction Certificate. This page is the workflow: when to order, who does it, what you get, what it costs, and how to act on the class. For the term itself and the full class table, see soil report (geotech).
When you order it
Order the soil report as early as the site is accessible and the building footprint is roughly known. Three trigger points:
- Before you commit to a slab price. The class is the single biggest driver of slab cost. Quoting a slab without it is a guess, and the gap between a Class M waffle slab and a Class H2 stiffened raft is real money.
- Before lodging in reactive-soil areas. Many councils and certifiers expect the classification with the application, and you cannot finalise footing design without it.
- Before purchase, on a risky block. On a known fill site, a steep block, or a Class P candidate, a report before settlement can save a buyer from a footing bill that swamps the land saving.
The common mistake is ordering too late, after the contract price is locked, then discovering the site is H2 or P and wearing the difference.
Who’s involved
| Role | What they do |
|---|---|
| Geotechnical engineer / accredited soil-testing lab | Drills the boreholes, logs the soil, issues the AS 2870 classification report |
| Builder | Provides site access and the proposed building footprint; books the test |
| Structural engineer | Uses the class and bore logs to design the footing and slab system |
| Certifier / lender | Generally requires the report before a Construction Certificate or finance drawdown |
You engage a geotechnical firm directly, or your building designer or structural engineer arranges it. Give them the site address, a site plan with the proposed footprint, and access (gates unlocked, dogs away, machine access if the rig needs it).
What you get
A typical report contains (verified 2026-05-25, AS 2870 / AS 1726 practice):
- Borehole or test-pit logs to the depth required for the site class
- Soil descriptions classified per AS 1726
- The site classification (A, S, M, H1, H2, E, or P)
- The characteristic surface movement (ys) value that quantifies expected ground movement
- Footing and slab recommendations, plus notes on drainage, fill, and trees inside the influence zone (TPZ)
For a small dwelling, extension, or pool, two boreholes on a flat site are usually enough. Larger or sloping sites need more, which is the main reason cost climbs.
What it costs
Indicative AU pricing (ex-GST, verified 2026-05-25 across multiple geotech providers):
| Job | Typical range |
|---|---|
| Flat block, small dwelling/extension, 2 boreholes | $450 to $800 |
| Standard residential lot classification | $700 to $1,200 |
| Large, sloping, or difficult-access site | $1,200 and up |
BAL (bushfire) and wind classifications are often offered as low-cost add-ons to the same site visit, and extra boreholes are charged per hole. Long travel and poor access push the price up. Treat anything under about $400 as suspiciously thin on boreholes.
How to read and action the class
The class tells you how reactive the ground is and therefore how much footing system you need:
- A and S (non to slightly reactive): standard slab solutions, lowest cost. Sand, rock, or light clay.
- M (moderately reactive): most metro clay sites. A stiffened slab to suit; the everyday case.
- H1 and H2 (highly reactive): heavy clays. Deeper edge beams or a raft, noticeably dearer.
- E (extremely reactive): severe shrink-swell, custom engineering.
- Class P (problem site): fill, soft soils, abnormal moisture or movement, mine subsidence. Always custom engineering, never a deemed-to-satisfy slab. A P classification is a flag to re-check your budget and program before you go further.
Hand the report straight to your structural engineer. Do not design footings off the class label alone: the engineer needs the ys value and the bore logs, not just the letter.
Common pitfalls
- Ordering after the price is locked. Get the class before you sign, not after.
- One borehole on a big or sloping site. Reactive ground varies across a block; too few holes can miss the worst of it.
- Assuming last door’s report applies. Classification is site-specific. A neighbour’s M does not make your block M.
- Letting the report go stale. On a long-delayed job, fill, drainage changes, or new trees can shift conditions; check currency before you build.
References
- AS 2870, Residential slabs and footings (site classification A to P) (verified 2026-05-25)
- AS 1726, Geotechnical site investigations (soil description) (verified 2026-05-25)
- AU geotechnical providers, residential soil-test pricing (verified 2026-05-25)
Related
- AS 2870: residential slabs and footings
- Soil report (geotech)
- Site classification
- Characteristic surface movement
- Class P site
- Decks (residential)
See also
Last updated: 2026-05-25. Verified: 2026-05-25. Quarterly review for currency.