Concurrent delay

Take one four-week overrun in which an employer variation and a contractor labour shortage are each independently critical across the same four weeks, with no express concurrency clause. Under English law the contractor gets four weeks and the owner gets no liquidated damages. Under AS 2124-1992 the contractor gets nothing and the owner gets all four weeks of liquidated damages. Same facts, same overrun, opposite results.

That spread is why a concurrency position taken without first identifying the governing law and the executed form is not an analysis. It is a guess wearing the vocabulary of one. The four-element entitlement test that every extension of time claim has to satisfy tells you whether there is a claim at all. Concurrency decides what survives of it.

What counts as concurrent delay?

"Concurrent delay" denotes at least five distinct things, and the choice between them changes the answer before any evidence is weighed. The narrow definitions (two events occurring at the same time whose effects are felt at the same time) capture almost nothing. The broad ones capture most overlapping critical delay on a live project. Most concurrency arguments are won or lost here, not on the facts.

The gap between the first and the fourth is the whole argument. SCL Protocol 2nd Edition (February 2017) Core Principle 10 sets a bar its own commentary says is almost never met. Schindler (2021 ONSC 283) expressly rejected any requirement of identical duration or precise parallelism, which makes it the broadest of the five and is a large part of why Canadian courts apportion more often than English ones. Two experts applying different definitions to the same as-built record will reach different answers, and neither is doing anything wrong.

The standard-setting bodies do not resolve it either. AACE International RP 29R-03, Forensic Schedule Analysis (rev. 25 April 2011), offers several working definitions rather than one and emphasises the technical difficulty of isolating impact. ANSI/ASCE/CI 67-2017, Schedule Delay Analysis (the full designation of the standard often shortened to "ASCE 67-17"), is reported to define concurrency as two or more critical delays occurring at the same time. A narrow formulation, though the text was not independently reviewed for this note. The US case law definition, from George Sollitt Construction Co. v United States, 64 Fed. Cl. 229, 239 (2005), has two aspects: a temporal one (the delays must affect the same delay period) and a causation one, each must be independently sufficient to cause the delay days attributed to it.

Pacing is not concurrency and should be separated out early. Where the contractor deliberately slows work in response to an owner delay that has already made that work non-critical, the slowdown is a reaction, not an independent cause. It only works as a characterisation if the election was documented at the time: in schedule narratives, resource plans, internal instructions or a notice to the owner. Reconstructed after the event, it reads as a rationalisation of the contractor's own inefficiency, and tribunals treat it that way.

The same four weeks, nine different answers

One fact pattern: a four-week overrun in which an employer variation and a contractor labour shortage are each independently critical over the same four weeks, and the contract contains no express concurrency clause. Across nine regimes the answer runs from four weeks of extension and no liquidated damages to no extension and the full four weeks of liquidated damages. Nothing in the table below is settled law in the regime it describes.

Illustrative: one fact pattern run through nine regimes, not a survey of outcomes.

The spread on a single fact pattern is 0 to 4 weeks of time and 0 to full liquidated damages. That is the argument for scoping every concurrency position to one regime and one executed form before anything else happens.

The underlying rules that produce those outcomes:

Jurisdictional. Only Scotland (Inner House), the US federal position (Fed. Cir.) and the express carve-out (Court of Appeal) are appellate. The rest is first instance or contractual.

Does concurrency cost you the money as well as the time?

Usually the contractor keeps the time and loses the money. Across England and Wales, the United States, Canada and FIDIC-governed arbitration, the most common outcome where genuine concurrency is found is a full or apportioned extension of time with no prolongation recovery. Concurrency converts a compensable delay into an excusable but non-compensable one: and, symmetrically, strips the owner of liquidated damages for the same period.

The reasoning differs by regime while the result converges. SCL Protocol 2nd Edition (February 2017) Core Principle 14 requires the contractor to separate the costs caused by employer delay from those caused by its own. US federal practice requires "a clear apportionment of the delay and the expense attributable to each party" (Blinderman Construction Co. v United States, 695 F.2d 552, 560 (Fed. Cir. 1982)). Neither is a rule that money is never available, both are rules about proof. Where the records permit the separation, the "time yes, money no" default softens, which is the single strongest argument for building the cost record contemporaneously rather than reconstructing it. The mechanics of what is recoverable once the time is granted sit in the prolongation and delay cost analysis.

Under FIDIC Red Book 2017 the "time yes, money no" outcome is often reached twice over. Sub-Clause 8.5 confers time, not money (grounds (c), (d) and (e) are time-only under the standard form) so a contractor relying on employer delay must locate its money entitlement in the governing law, and concurrency will meet it there as well.

Is English law settled on concurrent delay?

No. Every authority on the default position in England and Wales (the rule that applies absent express words) is first instance. The only Court of Appeal decision, North Midland Building Ltd v Cyden Homes Ltd [2018] EWCA Civ 1744, decided a question about express terms and expressly declined to resolve the default position. Anyone writing "English law grants a full extension of time for concurrent delay" is stating a strongly supported first-instance consensus, not binding appellate law.

The consensus itself is real and workable. Where two causes operate concurrently, one a Relevant Event and one the contractor's risk, and each is an effective cause of approximately equal causative potency, the contractor gets a full extension of time and no loss and expense. The strongest statement is Akenhead J in Walter Lilly & Co Ltd v Mackay [2012] EWHC 1773 (TCC), who also expressly rejected the Scottish apportionment approach as inapplicable in England. De Beers UK Ltd v Atos Origin IT Services UK Ltd [2010] EWHC 3276 (TCC) reaches the same result by a different route.

A citation warning worth carrying. The concurrency formulation associated with Malmaison is Dyson J at first instance, Henry Boot Construction (UK) Ltd v Malmaison Hotel (Manchester) Ltd (1999) 70 Con LR 32. It is regularly cited to a Court of Appeal neutral citation. That appellate decision was on a different point. Worse for the doctrine's foundations, the concurrency formulation was recorded as an agreed position between the parties, not a contested ratio.

Two lines of authority narrow it. Adyard Abu Dhabi v SD Marine Services [2011] EWHC 848 (Comm) holds that prevention requires an actual act that in fact caused delay to completion, so a contractor already running late on its own account cannot manufacture concurrency out of an employer act that would only have delayed a hypothetical unimpeded contractor. The same causation- first move disposed of the concurrency issue in Thomas Barnes & Sons plc (in administration) v Blackburn with Darwen Borough Council [2022] EWHC 2598 (TCC), where the court established the as-built critical path first and then asked what the effective cause of critical delay was in the relevant window. Earlier first-in-time reasoning runs through Royal Brompton Hospital NHS Trust v Hammond (No 7) (2001) 76 Con LR 148: recorded here as a High Court decision, though secondary sources attach "(No 7)" to a Court of Appeal decision, [2001] EWCA Civ 206, and neither form was confirmed against a judgment in this corpus, and Saga Cruises BDF Ltd v Fincantieri SpA [2016] EWHC 1875 (Comm).

Scotland diverges and the split is unresolved. City Inn Ltd v Shepherd Construction Ltd [2010] CSIH 68 permits apportionment by relative culpability and causative significance. It is Inner House authority, it has not been overruled, and it is unlikely to be reconciled with the English position absent a UK Supreme Court case.

Two negative findings matter here. No English decision between 2023 and August 2026 squarely reconsiders the default rule. The position remains as left by North Midland (2018) and Thomas Barnes (2022). And JCT 2024 still contains no concurrency clause, eight years after North Midland confirmed that a clearly drafted carve-out works. Parties who want the Cyden allocation must draft it in, and employer amendments increasingly do. NEC4 ECC contains no concurrency provision either. Contractor slippage is handled implicitly because the then-current Accepted Programme already carries it, and no English authority directly on NEC4 concurrency has been located.

Why the US position is a rule of proof, not a rule of entitlement

In United States federal practice the bar on recovery for concurrent delay is a rule of proof. Where both parties contribute to a delay, neither recovers damages "unless there is in the proof a clear apportionment of the delay and the expense attributable to each party" (Blinderman Construction Co. v United States, 695 F.2d 552, 560 (Fed. Cir. 1982)). Where the delays are genuinely severable and the evidence supports the split, apportionment is allowed and both parties recover pro rata. Concurrency does not extinguish the entitlement. It defeats the proof.

The burden allocation is the part most contractors get backwards. The common assumption is that concurrency is the owner's defence to prove. In federal practice the government raises and evidences it, usually through its own scheduling expert, but the persuasion burden on severability sits with the contractor.

Jurisdictional, United States federal practice only. Sauer is Federal Circuit. Sollitt is the Court of Federal Claims at first instance.

A contractor that proves a government delay and says nothing about its own concurrent delays will lose. Alares Construction, Inc. v Department of Veterans Affairs, CBCA 6149, 7071, 7597 (21 March 2025) is the instructive recent example, and it shows what period-by-period apportionment actually looks like: the contractor claimed the VA caused all 765 days of delay and sought extended general conditions for 653. The Board found 218 days of VA-responsible compensable delay, allocating each period separately and treating the contractor's parallel building-enclosure and interior-work delays as non-compensable.

The methodology findings in Alares travel further than the numbers. The Board adopted the government expert's critical-path analysis and rejected the contractor's schedule logic where it was unsupported or contradicted by contemporaneous project documentation, drawing adverse inferences from unexplained slippage and unexplained logic changes in the monthly updates. One caution on citing it: Alares is sometimes offered as a change-order release case. The Board upheld the reservation of rights in modification P00005 and rejected the implicit-release argument. The claim then failed on concurrency, which is an independent ground.

Canada apportions, and in Australia the printed form decides

Neither Canada nor Australia follows the English "full extension for concurrency" rule, and for different reasons: Canada because its judicial definition of concurrency is the broadest in the common-law world and its courts apportion, Australia because the answer is written into the standard form and two forms in common use answer it in opposite directions.

Canada, functional concurrency and apportionment

Canadian common-law provinces have adopted functional concurrency: overlapping delays to co-critical and co-controlling activities. Schindler Elevator Corporation v Walsh Construction Company of Canada, 2021 ONSC 283 (a neutral citation this corpus flags for cross-checking against CanLII before it is pleaded) expressly rejected any stricter requirement of identical duration or precise parallelism, which aligns Canada with the SCL Protocol's concurrency-of-effect category rather than with true concurrency, and makes the Canadian test wider than the English, US or ASCE formulations. Causation is the but-for test applied robustly and with common sense, with material contribution reserved for the exceptional case. CPM analysis identifying which activities were critical, who controlled them and what effect they had on completion is effectively required.

Walsh Construction v Toronto Transit Commission, 2024 ONSC 2782, endorsed the flexible overlapping-events approach and required a clear and rational expert opinion based on contemporaneous records. It tolerated departures from AACE RP 29R-03 (rev. 25 April 2011) because the recommended practice itself allows adjustments and requires subjective decisions, but that tolerance is conditional on the expert grounding those choices in contemporaneous documents and explaining them. It also rejected a bias challenge founded on the expert's contemporaneous involvement in the project.

No Canadian appellate decision squarely on concurrent delay was located for 2024–2026. The law rests on first instance authority, the same structural weakness as in England from a different starting point. CCDC 2 – 2020 GC 6.5 allocates delay by cause and says nothing about what happens when two causes overlap, so concurrency under Canadian standard forms is a pure common-law and evidential question. In practice it is often never reached, because Canadian courts enforce extension of time notice provisions strictly and without requiring the owner to prove prejudice.

Australia, AS 2124-1992 and AS 4000 give opposite answers

In Australia the divergence runs by contract form, not by common law. AS 2124-1992 clause 35.5 provides that where more than one event causes concurrent delays and the cause of at least one but not all of them is not a qualifying cause, then to the extent that the delays are concurrent the contractor is not entitled to an extension of time for practical completion. AS 4300-1995 is identical in substance. AS 4000 and AS 4902 clause 34.4 do the opposite: where qualifying and non-qualifying causes overlap, the Superintendent apportions the resulting delay according to the respective causes' contribution. AS 2124 remains widely used, particularly in government work.

The AS 2124 position is the closest thing in the common-law world to a printed-form version of the North Midland v Cyden allocation, except that it is in the standard form rather than a bespoke amendment, so it arrives without negotiation. (Note on clause numbering: the extension of time and delay clause numbering in the current AS 4000:2025 edition is disputed between published commentaries, and the standard is paywalled. Clause 34.4 is the apportionment provision in the AS 4000 lineage. Verify the numbering against the printed 2025 edition before relying on it in a submission.)

At common law, Australian first-instance authority defines concurrency narrowly. Australian Development Corporation Pty Ltd v White Constructions (ACT) Pty Ltd (1996) 12 BCL 317 at 345 holds that delays are not concurrent where the contractor-risk event starts first, causes actual delay and ends after the qualifying event has finished, functionally the same causation-first move as Adyard in England. No Australian appellate authority on concurrent delay or delay analysis was located for 2024–2026.

One live interaction is worth flagging. Australian forms give the Superintendent a unilateral power to extend time even where the contractor has not claimed, and that power must be exercised honestly and fairly (Peninsula Balmain Pty Ltd v Abigroup Contractors Pty Ltd [2002] NSWCA 211). Probuild Constructions (Aust) Pty Ltd v DDI Group Pty Ltd [2017] NSWCA 151 held that to claim liquidated damages the principal was obliged to exercise that power for delays it had caused. Under AS 2124, a principal that caused part of a concurrent delay and then levies liquidated damages must still confront that obligation, so the unilateral power may partially reopen what clause 35.5 closes. That interaction is under-litigated and genuinely open.

FIDIC 2017 supplies no rule at all

Under the FIDIC 2017 Second Edition (Red, Yellow and Silver Books, reprinted 2022), Sub-Clause 8.5's final paragraph provides that where an employer-responsibility delay is concurrent with a contractor-responsibility delay, the contractor's entitlement to an extension of time is assessed in accordance with the rules and procedures stated in the bespoke drafting document: and, if none are stated, as appropriate taking due regard of all relevant circumstances. That is a determination standard, not a rule of entitlement. It tells the Engineer how to decide, not what the answer is. The FIDIC 1999 First Edition is simply silent.

(Two drafting cautions. Published texts differ on one word in that paragraph: some quote "Special Provisions", one quotes "Particular Conditions". The Red Book 2017 uses "Special Provisions" as the defined term for the bespoke drafting document. Check the printed form before quoting the paragraph. And the grounds at Sub-Clause 8.5 (a)–(e) are commonly reproduced in paraphrase rather than verbatim, obtain the printed text before putting quotation marks around them.)

The practical consequence is that the governing law fills the gap, which is why the same FIDIC contract produces different concurrency outcomes in London, Edinburgh, Toronto, Sydney and Dubai. Under English law the Malmaison consensus applies (full extension, no prolongation cost) subject to any express Special Provision, which will be upheld after North Midland Building Ltd v Cyden Homes Ltd [2018] EWCA Civ 1744. Under Scots law, City Inn Ltd v Shepherd Construction Ltd [2010] CSIH 68 apportionment applies. Under Canadian law, functional concurrency and apportionment. Under civil-law systems, apportionment is the natural fit, because good faith and contributory-fault provisions allow a tribunal to reduce rather than choose, French Civil Code article 1104 and Swiss Code of Obligations article 44(1) are the clean examples. Gulf article numbering should be checked rather than assumed: the UAE Civil Code was replaced by Federal Decree-Law No. 25 of 2025 and articles were renumbered, so any pre-2026 UAE memorandum may cite provisions that have moved.

What parties actually do, in descending order of frequency: nothing, so the fallback discretion applies and the governing law supplies the substance, incorporate the SCL Protocol approach, giving time but not money, draft an employer-friendly express exclusion, which is upheld under English law after North Midland but may not survive in a civil-law forum where good faith and abuse-of-rights provisions cut against it, and which arguably strains FIDIC Golden Principle 2 (First Edition, 2019), or apportion, which is rare in FIDIC practice. If concurrency matters to the project (and on any large EPC it does) draft the model into the Special Provisions by name. "Assessed in accordance with the SCL Delay and Disruption Protocol, 2nd Edition (February 2017), Core Principles 10 and 14" is a complete and testable allocation. "As appropriate taking due regard of all relevant circumstances" is not.

What to establish before the delay happens

Find out which of the five definitions of concurrency, and which of the competing models of entitlement, your governing law and your executed contract put you in, and do it while the project is running rather than in the second round of expert reports. The five definitions produce answers from nil to a full extension on identical facts, and no amount of forensic skill applied afterwards will move a contract from one model to another. The only concurrency question that can still be influenced once a delay has started is what the contemporaneous record will say about it.

That last point is where three jurisdictions have independently converged. Thomas Barnes & Sons plc (in administration) v Blackburn with Darwen Borough Council [2022] EWHC 2598 (TCC) in England held that an expert is not confined to one SCL method and directed that the as-built critical path be established first, then the effective cause found. White Constructions Pty Ltd v PBS Holdings Pty Ltd [2019] NSWSC 1166 in Australia rejected both parties' delay experts and held that methodology must be driven by the factual evidence, the SCL Protocol not being a rule of law. Walsh Construction v Toronto Transit Commission, 2024 ONSC 2782 in Canada tolerated departures from AACE RP 29R-03 (rev. 25 April 2011) precisely because they were reasoned and grounded in contemporaneous records. In all three, the winning move was the contemporaneous record rather than the method label, which does not make the choice of delay analysis method irrelevant, only secondary to the evidence it is run on.

About this material Library content is general information about construction claim practice, not legal advice. Entitlement, deadlines and procedure are governed by your own contract and by the law of the place the work is performed. Reviewed August 7, 2026 · Report a correction