Claims · Delay Analysis

Concurrent Delay: Legal Framework and Expert Analysis

When multiple delays occur simultaneously, how are they analysed, how is responsibility allocated, and what entitlements follow?

7 min read · Updated 24/04/2026

In this article

1. Concurrent Delay: Definition and Legal Significance
2. Types of Concurrent Delay Events
3. Critical Path Analysis: The Foundation of Causation
4. Treatment of Concurrent Delay Under FIDIC
5. Allocation of Responsibility and Expert Analysis
6. Concurrent Delay Disputes in Arbitration
7. Expert Witness Methodology for Concurrent Delay

Key takeaway

Concurrent delay—where two or more independent delays occur at the same time and each affects the critical path—is one of the most contested issues in construction arbitration. Treatment depends on contract language: some FIDIC versions grant EOT for all compensable delays regardless of concurrency; others require apportionment. Expert analysis must isolate each delay event, assess its individual critical path impact, and quantify the total delay attributable to each responsible party.

1. Concurrent Delay: Definition and Legal Significance

Concurrent delay occurs when two or more independent delay events affect the critical path at the same time, and each event (standing alone) would cause delay to project completion. The cumulative effect is project delay, but causation becomes complex: How much delay is attributable to each event? Who bears responsibility for which portion?

Concurrent delay is legally significant because it affects entitlements to Extension of Time (EOT) and cost relief (prolongation damages). If the Employer causes one delay event and the Contractor causes another, occurring concurrently, the allocation of responsibility—and relief—depends on the contract language and the law.

Concurrent vs. Sequential Delay

The distinction is critical:

• Sequential Delay: Delay Event A occurs and is resolved. Delay Event B then occurs. Each event’s impact is isolated and additive.
• Concurrent Delay: Delay Events A and B occur during overlapping periods, both affecting the same critical path activity or activities. The total delay cannot simply be added; it must be analysed to determine how much delay each event independently caused.

2. Types of Concurrent Delay Events

Concurrent delays can arise from various sources:

• Employer + Contractor: The Employer delays in issuing drawings (Employer delay); simultaneously, the Contractor suffers a labour shortage (Contractor delay). Both events affect the same critical path activity.
• Employer + Force Majeure: The Employer delays in site access; concurrently, exceptional weather delays excavation.
• Contractor + Force Majeure: The Contractor’s supplier fails to deliver materials; concurrently, a natural disaster disrupts the supply chain.
• Multiple Contractor Events: Labour dispute + Equipment breakdown both occur during the same period, both affecting critical activities.

In each scenario, the question is: If only one event had occurred, how much delay would it have caused? And if only the other event had occurred, how much delay would that have caused? The answer determines allocation of responsibility.

3. Critical Path Analysis: The Foundation of Causation

Analysing concurrent delay requires rigorous Critical Path Analysis (CPA):

• Identify the Critical Path: The longest sequence of dependent activities. Any delay to a critical path activity delays project completion.
• Isolate Each Delay Event: For each event, determine which activities were affected and for how long.
• Calculate Time Impact: For each event, if it had been the only delay, how many days would the project have been delayed?
• Determine the “Critical Delay”: The delay event that would have caused the most project delay if occurring alone.

4. Treatment of Concurrent Delay Under FIDIC

FIDIC contracts grant EOT for delay events listed in Clause 20.1 (or Clause 17 in FIDIC 2017), but treatment of concurrent delay differs by edition and contract terms:

FIDIC 1999 Approach

FIDIC 1999 grants EOT for listed delay events without explicitly addressing concurrency. Most arbitrators interpret this as: the Contractor is entitled to EOT for any compensable delay event, even if concurrent with contractor-caused delay. The Contractor may not claim cost relief for the concurrent delay days, but EOT is granted.

Logic: The Employer’s breach (or listed event) entitles the Contractor to time relief. Concurrency with contractor delay does not remove that entitlement; it merely negates cost relief for the concurrent period.

FIDIC 2017 Approach

FIDIC 2017 is more explicit about apportionment where appropriate. The Engineer may assess concurrent delay and apportion EOT proportionately. However, most FIDIC 2017 contracts still grant EOT for compensable delay events regardless of concurrency with contractor delay.

Key Principle

Under FIDIC, concurrency does not typically deprive the Contractor of EOT for Employer-caused delays. However, the Contractor cannot claim cost relief (prolongation costs) for time periods in which the Contractor was also responsible for delay.

5. Allocation of Responsibility and Expert Analysis

Determining responsibility for concurrent delay requires meticulous analysis:

Step 1: Define the Baseline Schedule

The contractor’s original approved schedule (the “contract baseline”) is the reference. All delays are measured against this baseline.

Step 2: Identify Each Delay Event and Timeline

Document each delay event: the date it commenced, the date it ended or was resolved, the activities affected, and the responsible party (Employer, Contractor, or Force Majeure).

Step 3: Isolate Time Impact of Each Event

Using the schedule and Critical Path Analysis, determine how many days each event would have delayed the project if it had occurred in isolation. This requires schedule simulations: removing each event from the “as-built” programme and recalculating project completion date.

Step 4: Assess Concurrency and Apportionment

If events overlap, assess whether both events independently affected the critical path. If both are critical, the total project delay is the longest of the two delays (not the sum). If one event is critical and the other is sub-critical (i.e., has float), the critical event drives the total delay.

6. Concurrent Delay Disputes in Arbitration

Concurrent delay disputes are highly contentious in arbitration. Common issues include:

• Causation Disagreement: The parties disagree on which delay event was on the critical path or what the time impact of each event was.
• Apportionment: One party argues for no apportionment (all delay charged to the other party); the other argues for proportional allocation.
• Contractor Mitigation: The Employer argues the Contractor should have mitigated the impact of Employer delay by accelerating work or resequencing activities.
• Force Majeure Status: Disagreement on whether an event qualifies as force majeure or is a contractor-controllable event.

Arbitrators rely heavily on expert schedule analysis. A qualified delay analyst can model different scenarios and demonstrate the time impact of each event, strengthening or weakening the parties’ positions.

7. Expert Witness Methodology for Concurrent Delay

Analysing concurrent delay requires specialist expertise and rigorous methodology:

Data Requirements

A qualified expert requires:

• Contract Baseline Schedule: The original approved programme at contract signature.
• Updated Programmes: Monthly or periodic updates showing progress and replanning as events occurred.
• As-Built Records: Actual dates of key milestones, activity completions, and delay event commencement/resolution.
• Contemporaneous Correspondence: Emails, site instructions, meeting minutes documenting when delay events occurred and affected work.
• Cost Records: Timesheets, equipment hire records, invoices substantiating prolongation costs.

Analysis Approach

The expert typically uses one or more of these methodologies:

• Windows Analysis: Divide the project into monthly time windows. For each window, identify the critical path activities, assess what events occurred, and model the delay impact within that window.
• Time Impact Analysis: For each delay event, create a schedule simulation showing the project as-if the event had not occurred, then compare to actual completion date.
• Retrospective Analysis: Model the critical path at the time each delay event occurred, assessing its impact as if it were unknown at that point.

The expert must document assumptions, explain the methodology, present sensitivity analysis (testing the impact if key assumptions were different), and provide a clear, defensible conclusion on how much delay each event independently caused and, therefore, how much each responsible party is accountable for.

Navigate Concurrent Delay Disputes with Expert Analysis

Concurrent delay is one of the most complex and disputed issues in construction arbitration. Rigorous critical path analysis, detailed schedule modelling, and credible expert evidence are essential to resolve these disputes fairly. Our team of experienced delay analysts can isolate each delay event, quantify its independent impact, and prepare persuasive expert submissions to support your position in negotiation or arbitration.

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