Latent Conditions: Who Carries the Risk of What Is Underground

At 2:10 on a Wednesday afternoon, the piling rig on a Newcastle apartment job stops at six metres. The auger comes up scarred. Somewhere below the fill is a slab of old concrete and what looks like steel rail, the footprint of a rail siding nobody drew on anything.

The site foreman’s instinct is to get an excavator in and break it out before the concrete trucks arrive on Friday. The project manager’s instinct, two hours later, is to ask a different question. Was any of this in the geotechnical report, and who is paying for it?

What are latent conditions in construction?

Latent conditions are physical conditions on or near the site that differ materially from what a competent contractor should reasonably have anticipated at the time of tender. Rock, old footings, buried services, contaminated fill and groundwater are the usual suspects. Weather is excluded under the standard forms.[1]

The test is objective. It does not ask what this contractor actually expected. It asks what a competent contractor would have expected after examining the information the principal provided, making reasonable enquiries and inspecting the site and its surrounds.[1]

That makes a latent condition a question about information, not about ground. The same slab can be a latent condition on one job and the contractor’s own problem on another, depending on what the tender documents said and what a reasonable inspection would have shown.

How do AS 4000, AS 2124 and GC21 treat latent conditions?

Each standard form handles the risk differently, and the differences sit mostly in the notice provisions. Even small differences in wording can produce very different outcomes, so the table below is a starting point, not a substitute for the contract you signed.[1]

AS 4000:2025 is the first significant revision of the standard in almost 30 years, and it relaxed several notice requirements.[3] Many live contracts are still drafted on the 1997 edition, so confirm which one your job actually uses before relying on either.

28 days

Under AS 4000-1997 and AS 2124, costs incurred more than 28 days before the latent condition notice cannot be recovered.

AS 4000 clause 25.3, AS 2124 clause 12.4

Why the notice matters more than the ground

The notice clause is where good claims die. A contractor can be entirely right that the slab was unforeseeable and still recover a fraction of the cost, because the calendar started before anyone wrote anything down.

Take a condition that costs $3,000 a day in standing time, extra plant and rework for 60 days, a total of $180,000. The site team works around it for six weeks and gives written notice on day 43.

The difference between the first and second row is $42,000 of cost that was real, documented and caused by the condition. Nothing about the ground changed. Only the date of a letter.

The GC21 row is harsher still. Entitlement depends on the notice clause 37.3 requires, so a notice on day 43 puts the whole claim at risk.[5]

“Costs and delay incurred by the Contractor as a result of unexpected adverse Site Conditions before it gave the notice required by clause 37.3 must not be counted in any valuation or extension of time.”

GC21 (Edition 2), ACT Government modified version, clause 37.8[5]

What does “reasonably anticipated” actually mean?

This is the other half of most latent conditions disputes. Once notice is out of the way, the argument moves to whether the condition should have been expected.

The leading Victorian example is BMD Major Projects v Victorian Urban Development Authority. The contractor made two latent conditions claims worth about $7 million in total on a former quarry site.[6]

The first claim succeeded. Natural surface levels were materially lower than expected, and the court found that spotting the discrepancy in the geotechnical material would have needed a geotechnical engineer’s expertise, which an ordinary competent earthworks contractor would not have. The second claim, about oversized rock, failed, partly because the contractor had priced a contingency and so could not show it relied on the reports.[6]

The same case also shows notice is judged on its circumstances. Verbal notice was given on site when the condition was found and written notice followed ten days later, after more investigation. The courts accepted that as “forthwith”.[7]

$7 million

Two latent conditions claims in BMD v VicUrban. One succeeded on what a competent contractor could read from the geotech file. One failed because the contractor had priced a contingency.

Holding Redlich, on [2007] VSC 409 and [2009] VSCA 221

How principals shift the risk back to the contractor

The standard clause is a starting point, and principals routinely amend it. When reviewing tender amendments, look for three things.

Deleted or disapplied relief. Principals sometimes state expressly that no relief is available for latent conditions, or narrow the definition so fewer conditions qualify.[2] GC21 builds this in: if the Contract Information says the contractor bears the risk of adverse site conditions, the relief provisions simply do not apply.[5]

Reliance disclaimers. GC21’s site information clause says the principal does not guarantee the accuracy or completeness of certain site information, and the contractor warrants it has made its own enquiries, examined the site and allowed for the risks in its price.[5] A geotech report you cannot rely on is a very different thing from one you can.

Shortened notice periods. A 7-day written notice requirement on a job where the crew’s first instinct is to dig the problem out is a risk in its own right.

None of these is fatal to a tender. They are a pricing question. If the risk has moved to you, it belongs in the price or in a provisional sum, not in a claim you are unlikely to win.

Latent condition, provisional sum or variation?

These three get confused because they can all apply to the same trench.

A provisional sum is an allowance for work everyone knows is uncertain at tender, adjusted to actual cost. We cover how that adjustment works, and where the margin argument starts, in our post on provisional sums and prime cost items.

A latent condition is something nobody should reasonably have expected. If a provisional sum already covers excavation in rock, finding rock is unlikely to be a latent condition as well.

A variation is a change to the work the principal directs. Under AS 4000 the effect of a latent condition is a deemed variation, so it runs through the same valuation machinery, and the same disputes, described in how construction variations turn into disputes.[2]

The delay side runs on its own notices. A latent condition that holds up the job needs a separate extension of time claim under the contract’s EOT clause, with its own time bars, covered in our guide to extensions of time in Australian construction.[2]

What evidence to capture when you find one

The hour after discovery decides most of what follows. The standard forms expect notice, where possible, before the condition is disturbed, which means the evidence has to exist before the excavator does its work.

The site diary is where most of this either exists or does not. A diary entry written that afternoon, with photos attached, is worth more than any reconstruction prepared for an adjudicator three months later.

What good looks like

The contractors who recover latent conditions costs are rarely the ones with the best legal argument. Their process made the evidence and the notice automatic.

• The contract’s latent conditions clause, notice period and any amendments are summarised for the site team before work starts, not discovered after the slab

• Tender site information is filed where the project team can reach it on site, against the location it describes

• Discovery triggers a same-day written notice, even a short one, followed by the detailed statement

• Photos go in before the excavator does, tagged to the location and the diary entry

• Latent conditions costs are captured against their own cost code from day one

• Every notice, request for information and superintendent response sits in one register with dates

The Australian context

Residential work has its own rules. In Victoria, the builder must obtain foundations data before the owner signs the building contract, and Consumer Affairs Victoria tells owners they should not have to pay extra to deal with problems, such as excavating rock, that the builder should have identified from that data.[8] The practical effect is that much of the latent condition argument is decided at the soil test, before the contract exists.

On commercial and government work, the form matters as much as the facts. A contractor running an AS 4000-1997 job, an AS 2124 legacy contract and a GC21 government project at the same time is working to three different notice regimes on the same kind of discovery. For how the standard forms compare more broadly, see types of construction contracts.

This is general information rather than legal advice. The clause in the contract you signed, with every amendment, decides the answer.

Where Plexa fits

In Plexa, the site diary records the day’s workforce, work completed, weather and site notes, with photos captured in the field and attached to the entry. The photos of that slab, taken before anyone touched it, sit with the diary entry for that day rather than on someone’s phone.

The Correspondence module manages contract instructions, builder’s directions, extensions of time and general notices, all version controlled and tracked for closure. The latent condition notice, the superintendent’s request for more information and the EOT claim that follows each have a date on the register, not in an inbox.

On the money side, costs can be tracked against their own cost code in the budget, and the Head Contract module raises claims and variations linked to the subcontractor variations underneath. When the latent condition becomes a deemed variation, the supporting cost is already coded.

Back on that Newcastle site, the excavator does not start until the engineer has photographed the slab, logged it in the diary and sent a short written notice the same afternoon. The rail siding costs what it costs. The claim for it starts on day one, not day 43.

Frequently asked questions

What is a latent condition in construction? A physical condition on or near the site, excluding weather, that differs materially from what a competent contractor should reasonably have anticipated at tender, having examined the information provided, made reasonable enquiries and inspected the site.[1]

Who pays for latent conditions? It depends on the contract. Under unamended AS 4000 and AS 2124 the principal generally pays through a variation or valuation, if the contractor gives proper notice. Many contracts are amended to move the risk to the contractor, and GC21 lets the principal do this through the Contract Information.[2][5]

How quickly do you have to notify a latent condition? It varies by contract: promptly under AS 4000-1997, as soon as practicable under AS 4000:2025, forthwith under AS 2124, and within 7 days in writing under the ACT-modified GC21. Where possible, notice should be given before the condition is disturbed.[2][3][4][5]

Can you claim costs incurred before the latent condition notice? Only partly, and sometimes not at all. AS 4000-1997 and AS 2124 exclude costs incurred more than 28 days before the notice. The ACT-modified GC21 excludes all costs and delay incurred before the notice.[2][4][5]

Is a latent condition a variation? Under AS 4000 the effect of a latent condition is treated as a deemed variation, so it is valued through the variation provisions. Delay needs a separate extension of time claim under the contract’s EOT clause.[2]

Are latent conditions different in residential building? Yes. Domestic building legislation adds its own rules. In Victoria the builder must obtain foundations data before the owner signs the building contract, and owners should not pay extra for problems the builder should have identified from it.[8]

Related reading

The time side of a latent condition is covered in extensions of time in Australian construction. The valuation disputes that follow a deemed variation are the subject of how construction variations turn into disputes. And the record that proves what you found is covered in the site diary.

If you want to see how notices, diary entries and photos come together on a live project, book a 30-minute demo with the Plexa team.