Claims » Extensions of Time

Concurrent Delay — Attribution and Entitlement

Concurrent delay is the most technically challenging concept in construction delay analysis — and the one most frequently misunderstood or oversimplified. When delays from both parties operate simultaneously, entitlement to time and money is rarely straightforward.

4 min read · Updated 21/04/2026

In this article

1. What concurrent delay actually means
2. The Henry Boot v Malmaison principle
3. The separate question of prolongation costs
4. Practical application
5. Risks and mitigation
6. Conclusion

Key takeaway

Under English law, concurrent contractor delay does not defeat the EOT entitlement arising from a concurrent employer risk event — the contractor gets the time. But the prolongation cost entitlement is different: costs for a period during which the contractor’s own default is also operative are typically not recoverable. Time and money travel on separate tracks when delays are concurrent.

1. What concurrent delay actually means

Concurrent delay arises in several forms. The classic case involves two independent events, one from each party’s risk category, occurring at exactly the same time and each independently causing delay to completion of the same duration. This is “true” concurrency, and it is relatively rare in practice. More commonly, the delays overlap partially, or one is the dominant cause while the other is subsidiary. The analysis is further complicated by the difficulty of demonstrating, with the contemporaneous records typically available on a construction project, what would have happened “but for” each delay event.

2. The Henry Boot v Malmaison principle

The Society of Construction Law’s Delay and Disruption Protocol (2nd edition, 2017), Core Principle 10, gives similar guidance: where there is true concurrent delay, neither party should benefit or be disadvantaged, and the contractor is entitled to EOT but not to prolongation costs. This is the practical consensus in UAE delay claims, particularly those heard at DIAC.

3. The separate question of prolongation costs

On the separate question of prolongation costs during a concurrent delay period, the English position — though more contested — is that the contractor cannot recover costs for a period during which its own default is also causing delay. This was confirmed in Multiplex Constructions (UK) Ltd v Honeywell Control Systems Ltd [2007] EWHC 447 (TCC).

The practical consequence is that EOT and prolongation cost travel on separate tracks in concurrent-delay analysis. Winning the EOT is not the same as winning the prolongation claim — and a sophisticated contractor frames its case accordingly, focusing its prolongation recovery on periods where employer delay was dominant or exclusive.

4. Practical application

For contractors

The existence of concurrent delay does not defeat the EOT entitlement for the employer’s risk event. Fight for the EOT. The prolongation cost claim for the concurrent period is more difficult — focus the cost claim on periods where the employer’s delay was dominant or exclusive, and present those periods separately with distinct causation analysis.

For employers and contract administrators

Concurrent delay analysis must be rigorous. Simply asserting that the contractor caused concurrent delay does not defeat the EOT entitlement. The employer must demonstrate, with programme evidence, that the contractor’s delay would have prevented completion regardless of the employer’s delay — and that demonstration requires detailed delay analysis from contemporaneous records.

5. Risks and mitigation

For contractors, the risk of poorly documented concurrent delay periods is that the entire delay period (employer and contractor combined) is treated as contractor-caused, defeating both the EOT and the cost claim. For employers, the risk of ignoring concurrent employer delay is that time goes at large, defeating the liquidated damages provision entirely.

Maintain detailed contemporaneous programme records throughout the project. Analyse delay events on a period-by-period basis, identifying dominant causes and concurrent periods. Apply SCL Protocol methodology consistently. In significant disputes, engage a delay analysis expert who can construct a programme-based concurrent delay analysis using the available records — the analysis is typically only as good as the records permit.

6. Conclusion

Concurrent delay requires careful, evidence-based analysis. The legal principles are settled in English law but their application to specific factual scenarios is rarely simple. The contractor who understands the distinction between EOT entitlement (generally preserved) and prolongation cost entitlement (more restricted in concurrent periods) is better positioned to pursue its claims with realism and precision.

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