When construction projects fall behind schedule, the reason is rarely simple. Often, multiple parties contribute to delays that overlap or occur at the same time, creating what is known as concurrent delay. These situations can have serious cost and liability implications for both contractors and owners.
This communique explores the leading Canadian case and the basic principles governing the allocation of concurrent delay between the parties responsible for that delay, as well as key takeaways to consider should a future construction project experience such an issue.
What is a concurrent delay in construction projects?
Concurrent delay occurs when two or more independent events, attributable to different parties, delay the completion of a project while either occurring at the same time or overlapping. These delays may involve separate activities, but each affects the project’s critical path.
How did the Court approach concurrent delay in Schindler?
The leading case on the apportionment of concurrent delay in Canada is the 2021 Ontario Superior Court of Justice (the “Court”) decision in Schindler Elevator Corporation v Walsh Construction Company of Canada (“Schindler”).[1] In this case, the prime contractor, Walsh Construction/Bondfield Partnership (“WBP”), hired Schindler Elevator Corporation (“SEC”) to supply and install ten elevators for a hospital construction project. The project experienced delay, and WBP commenced an action to recover its delay costs. WBP asserted that SEC, along with other subcontractors, had caused concurrent critical path delays, and therefore SEC should be liable for a proportionate share of those costs.
At trial, both sides tendered critical path method (“CPM”) schedule analyses from experts regarding responsibility for the critical path delay experienced on the project. Notably, the Court did not give weight to either analysis in arriving at its decision, having found issues with the impartiality and reliability of both.[2]
In order to meet its evidentiary onus in the absence of a reliable CPM schedule analysis, WBP, as the party claiming delay damages, had to demonstrate the impact of SEC’s delayed work on subsequent work and sequencing.[3] WBP did not meet this onus, largely because the actual critical path of the project had not been identified, including which activities were on it, who was responsible for those activities, and whether any of them were delayed.[4] This made it difficult for the Court to determine whether any critical path activities following SEC’s elevator work were impacted by SEC’s delays such that SEC could be said to have materially contributed to the overall project delay.[5]
What legal principles did the Court adopt on concurrent delay?
Ultimately, the Court found that SEC completed the elevators late but did not cause or materially contribute to any critical path delay to the overall project, largely due to the absence of reliable expert analysis or clear evidence of causation.[6]
In arriving at its decision, the Court made two important findings with respect to the analysis of concurrent delay:
- Definition of concurrent delay: The Court adopted the definition of concurrent delay put forward by Glenn Grenier in his 2006 article titled “Evaluating Concurrent Delay – Unscrambling The Egg,” namely that concurrent delay exists where the delays to co-critical and co-controlling activities overlap.[7] In making this finding, the Court rejected a stricter definition put forward by SEC’s expert, which required that the delays be “parallel in time and identical in duration” to be considered concurrent.[8]
- Causation standard: The Court found that the assessment of concurrent delay on a complex construction project “will often give rise to a material contribution assessment for causation,” rather than a traditional “but-for” analysis.[9] Although the “but-for” test remains the primary test for determining causation, the “material contribution” test could properly be applied where:
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- it is impossible for the plaintiff to prove that the defendant’s negligence (or breach of contract) caused the plaintiff’s loss using the but-for test; and
- it is clear that the defendant breached a duty of care (or contract), thereby exposing the plaintiff to an unreasonable risk of loss, and that the plaintiff suffered that very loss.[10]
Reading between the lines, it appears that the Court considered the material contribution assessment to better align with the nature of concurrent delay, the analysis of which requires breaking the overall delay into its component parts and apportioning time, responsibility, and costs.[11] The but-for approach, on the other hand, was less suitable for this analysis as it could result in one party being held solely responsible for delay even where the evidence supported a finding that multiple parties were responsible.[12]
Is the “material contribution” test the right approach?
In her 2024 article titled “Concurrent Delay and Causation,” Beth Allard questioned whether the Court in Schindler needed to rely on the “material contribution to risk” test at all. She argues that a robust, common-sense approach to the “but-for” causation test can still yield fair results.
The simple but-for test establishes causation by asking: but for the alleged cause, would the effect have occurred? If the answer is no, the alleged cause did in fact cause the effect. Under this simple but-for test, two concurrent contributors to delay on a construction project could not both be classified as legal causes of the delay, even when it is obvious that one or both contributors caused the delay.
The material contribution to risk test addresses this shortcoming of the but-for test by eliminating the need to prove strict but-for causation. Eliminating this requirement is a significant departure from the traditional causation analysis; accordingly, resort to the material contribution test is rare and available only when proving but-for causation is impossible – meaning that it is impossible to show, on a balance of probabilities, that a specific party in fact caused a loss.
An example of an appropriate application of the material contribution test occurred in Cook v Lewis.[13] In this case, three men were out hunting. Two of them fired simultaneous gunshots, and one shot struck a fourth hunter, who was injured. It was impossible to prove which hunter’s gun caused the injury given the state of ballistic evidentiary techniques available at the time, so the simple but-for test could not prove that either hunter caused the injury. That said, both hunters had breached their duty of care to the injured party and had subjected him to unreasonable risk of injury – a risk that ultimately materialized.[14]
As Allard explains, it will rarely be impossible to show, on a balance of probabilities, that a specific party caused a loss due to concurrent delay on a construction project, because a detailed CPM analysis will overcome this impossibility. Although the Court referenced and facially applied the material contribution to risk test in Schindler, it did not explain how the test’s pre-requisite of impossibility was met. That said, despite using the language of the material contribution test, the Court appears to have engaged in a robust, common-sense approach to the but-for test.
This robust but-for test was discussed in the dissent of Justice McLachlin (as she then was) in Sunrise Co v Lake Winnipeg (The), and further developed by Chief Justice McLachlin (as she then was) in Clements (Litigation Guardian of) v Clements.[15] The “robust” component of this test is the introduction of “a factor other than pure causation” where there are concurrent causes of a loss, such as the apportionment of concurrent delay among its causes.[16] Under a robust, common-sense approach to but-for causation, where more than one party causes a loss, apportionment is necessary to ensure fairness and justice between the parties, so that each is responsible only for their respective share of the loss.
Key takeaways
An overall delay to a construction project caused by delays to two or more concurrent critical path activities cannot properly be allocated to a single party using the simple but-for test. To overcome this problem, courts have articulated the following principles:
- The applicable contract must be analyzed to determine whether a contributing delay has been categorized and whether its corresponding liability had been allocated to a party;
- The evidentiary onus is on the party seeking relief to prove a causal connection between the contributing delay and the loss suffered;
- The but-for test for causation should be applied using a robust, common-sense approach;
- A CPM analysis will likely be the best tool to meet the evidentiary onus for causation;
- Where no CPM analysis is available to precisely apportion delay, courts will “do the best they can” with satisfactory evidence available; and
- Courts may resort to the material contribution to risk test if proving causation is truly impossible.
Conclusion and next steps
Concurrent delay is among the most challenging issues in construction litigation. Understanding how Canadian courts interpret causation, and preparing detailed scheduling evidence from the outset, can make the difference between recovery and denial of claims.
For guidance on managing delay risk or litigating construction disputes, contact Miller Thomson’s Construction Litigation Team. Subscribe to our newsletters to stay up to date on emerging case law and industry insights.
A concurrent delay occurs when two or more independent delays, attributable to different parties, delay the completion of a construction project. These delays must overlap but do not need to be of identical duration or have the same start and end dates. Because these delays overlap, allocating responsibility and cost recovery becomes complex.
Canadian courts examine how each delay affected the project’s critical path and rely on clear evidence, such as scheduling records, contractual clauses, and expert testimony, to assign liability. The party seeking compensation must prove that another party’s delay directly impacted completion. Courts will interpret the contract’s delay provisions first, then apply a robust, common-sense but-for analysis to assess causation. If precise apportionment is difficult, courts may divide responsibility proportionally based on the available evidence.
The “but-for” test remains the default rule for determining causation. Courts may only turn to the “material contribution” test when it is truly impossible, rather than merely difficult, to prove causation on a balance of probabilities because multiple overlapping causes cannot be disentangled. In construction cases, this situation is rare, as a detailed Critical Path Method (CPM) analysis often allows causation to be established. In Schindler,the Court referenced the material contribution test but effectively applied a practical, evidence-based version of the but-for analysis.
The most persuasive evidence is a well-prepared CPM schedule analysis that identifies:
– which activities were on the critical path;
– who was responsible for each activity; and
– how the delay of each activity affected project completion.
Supported by contemporaneous project documentation, this evidence enables the court to assess causation and apportion responsibility fairly. Without a credible CPM analysis, a delay claim may fail for lack of proof.
[1] Schindler Elevator Corporation v Walsh Construction Company of Canada, 2021 ONSC 283 [Schindler].
[2] Ibid at paras 91-96, 312, 333-334.
[3] Ibid at paras 292, 337.
[4] Ibid at paras 319-320.
[5] Ibid at paras 339-347.
[6] Ibid at para 343.
[7] Ibid at para 346; G. Grenier, “Evaluating Concurrent Delay – Unscrambling the Egg” (2006) Construction Law Reports, 53 CLR (3d) 46.
[8] Schindler, supra note 1 at para 346.
[9] Ibid at para 294, citing Hanke v Resurfice Corp, 2007 SCC 7 at paras 21-25 [Hanke].
[10] Ibid at para 293, citing Hanke.
[11] Ibid at para 303
[12] Ibid at para 346.
[13] Cook v Lewis, [1951] SCR 830, [1952] 1 DLR 1 [Cook].
[14] Ibid at paras 18-19.
[15] Sunrise Co. v Lake Winnipeg (The), [1991] 1 SCR 3, 77 DLR (4th) 701 [Sunrise]; Clements (Litigation Guardian of) v Clements, 2012 SCC 32 [Clements].
[16] Sunrise, supra note 15 at para 83; Clements, supra note 15 at para 46.
