Extensions of Time in Australian Construction: When to Claim, How to Prove It, What They Really Cost

It is 3:40pm on a Wednesday. The excavator has stopped in a service trench because the demo crew uncovered rock that was not in the geotech report. The site engineer photographs it, calls the contracts administrator, and both agree they will “write it up properly on Friday when the week calms down.” Friday becomes the following Tuesday. By the time anyone drafts the paperwork, the contract notice window for an extension of time claim has closed, the rock is gone, and the only record is a group chat and one blurry photo.

This is not a rare failure. It is how most EOT claims in Australian construction quietly die, not because the delay was not real, but because the clock ran out while the site kept moving.

What an EOT actually is

An extension of time moves the contractual Date for Practical Completion, and with it, the point at which liquidated damages begin to accrue. Under AS 4000, AS 4902 and AS 2124, it is granted for a “qualifying cause of delay,” a defined list that includes principal-caused delays, latent conditions, industrial action and specified weather [1]. Under HIA and Master Builders residential contracts, the equivalent is an extension of the building period, granted where the builder serves written notice on the owner inside the contract window [2].

Without a granted EOT, LDs accrue, prolongation costs are unrecoverable, and every day of unclaimed delay is a day the builder funds the principal’s slip out of margin.

Why 74% of Australian builders end up here

The pressure is not hypothetical. QBE’s 2024 sector outlook found 74% of Australian builders and 62% of developers experienced project delays in the preceding year [3]. ABS Building Activity data shows the average house completion time rose from 6.6 months in September 2019 to 9.9 months by June 2024, a 50% increase [4]. Delay is the default condition of an Australian build.

74% of Australian builders experienced project delays in the year to 2024, alongside 62% of developers.

QBE Australian Construction Sector Outlook 2024

The trap is that delay is common but the EOT process is unforgiving. The contract does not care that the trade market is tight or that the site team is running three jobs. It cares about notice, cause, and evidence, in that order.

The two clocks that never sync

Every EOT contract runs on two clocks. The contract clock starts when the delay event happens, or when the contractor becomes aware of it. Under Master Builders ACT residential contracts the builder has 20 business days from the delay to serve notice [5]. Under HIA major residential contracts it is also 20 working days from when the builder becomes aware of the cause and extent [2]. Under AS 4000 Clause 34.3, the contractor has 28 days from when it should reasonably have known [1].

The site clock runs on a different frequency. A delay on Wednesday competes with a defect walk on Thursday and a subcontractor no-show on Monday. The notice gets drafted when someone finally has 40 minutes, which is often three weeks later. By then the contract clock has run, and even a well-founded claim is exposed.

20 to 28 days: the window most Australian building contracts give a contractor to serve an EOT notice, running from the delay event itself.

AS 4000-1997 Clause 34.3; HIA and MBA residential contract EOT clauses

What you actually have to prove

An EOT claim survives on three legs. Miss any one and it collapses.

1. A qualifying or compensable cause of delay the contract recognises.

2. A cause-and-effect impact on the critical path, not just work that happened.

3. Notice served in the form and within the window the contract requires.

Cause and effect is where most claims fail. It is not enough to say “we lost four days on the trench.” The claim has to show the trench sat on the critical path, that the four lost days pushed a downstream activity, and that the activity moved the Date for Practical Completion. Straightforward to capture live against the programme. Almost impossible to reconstruct three months later from memory and email.

“The importance of complying with the contractual requirements for claiming extensions of time is critical, especially if entering into contracts with a discretionary EOT clause which can only be exercised in favour of the principal.”

Kreisson Legal, case note on Probuild Constructions v DDI Group [2017] NSWCA 151

Prolongation costs are not delay damages

Two terms get used interchangeably and should not be. Prolongation costs are the time-related site costs that keep running while the completion date extends: supervision, site sheds, plant hire, temporary services, insurances, project management overhead. On a $20M commercial build they routinely run into tens of thousands of dollars per week.

Delay damages under AS 4000 Clause 34.9 are the broader recovery available where the qualifying cause is also compensable, meaning the principal carries the contract risk for it [1]. Recovery is only ever what the contractor can prove, at actual cost, tied to actual programme impact. The claim that pairs a contemporaneous cost record with a programme fragment showing critical path impact gets paid. The rest get negotiated down.

Why most EOT claims lose

The pattern is consistent across NSW, VIC and QLD adjudications. Notice arrives late or in the wrong form. There is no contemporaneous record, only a reconstructed narrative. Programme impact is analysed at claim time, not at delay time, so cause and effect becomes a lawyer’s argument rather than an engineer’s record. The notice gets bundled inside a variation claim months later, blurring two separate mechanisms.

Even where the prevention principle might have offered a safety net, Corrs’ analysis of Probuild v DDI notes that principals are increasingly amending standard forms to exclude it [7]. A contract with time bars and no unilateral EOT power leaves the contractor with no recourse once the notice window is missed. The window becomes the entire claim.

What good looks like

The teams that win EOTs do not have better lawyers. They have better records, captured earlier. A delay event goes into the site diary the same day, tagged with the qualifying cause, initial impact estimate, and photos. A draft notice is generated from that entry inside the contract window. A programme fragment showing the impacted activity and its critical path relationship is attached at first service and refined as the impact clarifies.

When that discipline holds:

• The notice is served inside the contract window every time, without heroics.

• Cause and effect exists as a live record when the claim is assessed.

• Prolongation cost claims are tied to actual, documented time-related costs.

• The RFI, delay event, diary entry, and notice all live in one connected record.

• Superintendents receive claims they can assess on first reading, not dispute.

Where Plexa fits

Plexa’s Correspondence and Program modules close the gap that kills most EOT claims. A delay event is logged in the site diary the day it happens, with photos, weather, and cause attached. The EOT notice is generated from that record inside the contract window, routed through the workflow tool to the CA and superintendent, and stored in the correspondence register alongside the RFI thread and any linked variation. Programme impact is tracked in the live schedule against the critical path, not stitched together from spreadsheets months later.

Return to that Wednesday afternoon. With a connected record, the trench rock is logged as a delay event by 4pm, the initial notice is generated inside the contract window, and the programme fragment is attached by Friday. The claim that reaches the superintendent is a document, not a reconstruction. That is the difference between an EOT that gets granted and one that becomes a dispute.

Related reading

The same fault line runs through most schedule work: the programme reflects last Thursday, the site moved on Wednesday. We covered that pattern in why Australian construction schedules fail. Because delay events so often start as information that never arrived on time, it pairs with what a good RFI process actually looks like in construction. For the margin side of the story, see why construction profit margins are tighter than they should be. EOTs and variations often ride on the same delay event, and we cover the variation side in our companion piece on construction variation management.

If you want to see how Plexa keeps delay events, notices, programme impact, and prolongation cost records in one connected file, book a 30-minute demo with the Plexa team.