Concurrent delay is not itself an analysis method. It is a concept that cuts across every method, and it is the single issue most likely to reduce the entitlement or quantum of an otherwise meritorious delay claim. A contractor who has documented owner-caused delay, quantified it carefully using a defensible AACE method, and presented it cleanly can still see their claim reduced or denied because concurrent contractor-caused delay existed during the same period. An owner who believes they have a solid defense against a contractor's claim can find that defense weakened because concurrent owner-caused delay was happening at the same time.
Understanding concurrent delay requires separating what the term means from how different jurisdictions and protocols treat it, and recognizing that the definition itself is contested. Practitioners who treat concurrency as a settled concept get surprised by how much room for argument remains.
The Core Idea
Concurrent delay exists when two or more delays occur during the same period, caused by different responsible parties, each of which is independently capable of delaying the critical path and thus the project completion date. The textbook example is a rainy week that delays excavation (excusable but non-compensable) occurring at the same time the owner's late permit delays the same excavation (compensable). Both would have delayed the project if the other had not existed. Both are concurrent.
The consequences of concurrency fall into two categories: entitlement (whether a party gets time, money, or both) and quantum (how much). Both are affected and both vary by jurisdiction.
Literal Versus Functional Concurrency
One of the first disputes in any concurrency analysis is how concurrency is defined.
Literal concurrency requires the two delays to overlap in time on the same critical path. If owner-caused delay occurs on critical path activity A during week 5, and contractor-caused delay occurs on critical path activity B during week 5, they are concurrent under the literal view.
Functional concurrency takes a broader view. Delays do not have to be simultaneously on the critical path to be concurrent. If contractor-caused delay would have affected the critical path had owner-caused delay not been consuming float, the contractor's delay is functionally concurrent.
The distinction matters because functional concurrency captures more situations as concurrent, typically to the disadvantage of the contractor. Literal concurrency is narrower and more favorable to the contractor's claim. Courts, tribunals, and protocols take different views, and contract language sometimes specifies which theory applies.
How Different Frameworks Treat Concurrency
AACE RP 29R-03 discusses concurrency at length and identifies multiple approaches without prescribing one. The RP acknowledges that concurrency analysis depends heavily on the analytical method being used and on the factual context.
AACE RP 10S-90 (cost and schedule risk analysis) and other AACE documents touch on concurrency in related contexts.
The Society of Construction Law Delay and Disruption Protocol (2nd Edition, 2017) takes a specific position: true concurrency is narrowly defined, pacing delay is distinguished from concurrent delay, and where true concurrency exists, the contractor is generally entitled to an extension of time but not to compensation for the owner-caused portion. This is the "time but not money" position.
U.S. case law varies significantly by jurisdiction but generally recognizes that concurrent contractor-caused delay bars compensation for the concurrent period, though not necessarily time extension. Some jurisdictions apportion damages based on causation, some apply all-or-nothing rules.
English case law has evolved through cases like Walter Lilly v. Mackay and others, generally aligning with the SCL Protocol position while recognizing factual nuance.
Australian and Canadian approaches have their own variations, and international arbitrations often default to SCL Protocol principles by agreement.
The practical reality is that concurrency treatment is jurisdiction-dependent, contract-dependent, and fact-dependent. An analyst who assumes a single universal rule will be wrong in some forums.
Pacing Delay: The Related Concept
Pacing delay is a defense contractors sometimes raise against owner claims that contractor-caused delay contributed to late completion. The argument is that the contractor paced their work (deliberately slowed down) in response to an owner-caused delay that was already extending the project, and therefore the pacing is not a true delay but a reasonable response to conditions outside the contractor's control.
To sustain a pacing defense, the contractor typically has to show:
- An existing owner-caused delay that was already affecting the critical path.
- A reasoned decision to pace work in response to that delay.
- Contemporaneous documentation of the pacing decision and its rationale.
- Ability to resume normal pace when the owner delay ends.
Pacing is easier to allege than to prove. Contractors who invoke pacing without contemporaneous documentation typically fail on the defense.
The Analytical Implications
Each delay analysis method handles concurrency differently, and the choice of method shapes what the analysis can say about concurrency.
- Observational methods (MIPs 3.3, 3.4, 3.5) identify concurrency by examining what was happening on the critical path during each window. They rely on the contemporaneous record to show concurrent events.
- Modeled additive methods (MIPs 3.6, 3.7, including TIA) can obscure concurrency because each delay event is modeled independently. Summing independent TIA results can produce totals that exceed the actual project delay, which is a signal that concurrency was not properly handled.
- Modeled subtractive methods (MIPs 3.8, 3.9, Collapsed As-Built) can address concurrency through multiple simulations but require explicit analytical choices that have to be defended.
Regardless of method, the analyst has to decide what theory of concurrency to apply, document the choice, and apply it consistently.
Practical Discipline
For practitioners dealing with concurrent delay in a live dispute:
- Identify the jurisdiction and applicable framework early. The answer to "is this concurrent" depends on where the dispute will be resolved.
- Read the contract carefully. Some contracts specify concurrency treatment, float ownership, and pacing explicitly. Contract language can override default rules.
- Document contemporaneously. Pacing defenses, concurrent delay identification, and causation attribution all depend on contemporaneous records. After-the-fact reconstruction is weaker.
- Use an analytical method that can show concurrency clearly. Observational period methods are generally better at displaying concurrency than aggregated modeled methods.
- Be explicit about concurrency theory. Don't let the method silently apply a theory the analyst has not thought through.
- Distinguish true concurrency from pacing. Conflating the two weakens both positions.
Where It Sits in the Bigger Picture
Concurrency is the concept that separates delay analysts from schedule preparers. Anyone can identify that a project finished late. Determining who bears the consequences requires working through concurrency, pacing, causation, and the applicable legal framework, and doing so with the rigor that a tribunal or court will demand.
The practical takeaway is that concurrency cannot be an afterthought. It has to be identified during the analysis, addressed explicitly in the report, and defended on cross-examination. Claims that ignore concurrency lose ground they should not have to give up. Claims that address it honestly and thoroughly survive scrutiny that sinks less disciplined work.
References
- AACE International, Recommended Practice No. 29R-03, Forensic Schedule Analysis (current edition). See the discussion of concurrent delay across multiple MIPs.
- AACE International, Professional Practice Guide No. 20 (PPG #20), Forensic Schedule Analysis (2nd Edition). Collected papers on concurrent delay, including Brasco and Anzidei's "Concurrent Delay and the Critical Path: Views from the Bench," Sadauskas and Wodiska, and Khademagha on literal versus functional concurrency theories.
- Society of Construction Law, Delay and Disruption Protocol (2nd Edition, 2017). See the sections on concurrent delay and pacing.
- U.S. case law on concurrency varies by jurisdiction; representative cases include Williams Enterprises, Inc. v. Strait Manufacturing & Welding, Inc. and federal Board of Contract Appeals decisions.
- English case law, including Walter Lilly & Company Ltd. v. Mackay [2012] EWHC 1773 (TCC) and subsequent decisions.
- Galloway, P.D.; Nielsen, K.R. "Concurrent Schedule Delay in International Contracts," Nielsen-Wurster Group.