Concurrent delay — where two or more delay events, one Employer-caused and one Contractor-caused, operate simultaneously on the critical path — is one of the most contested areas of contractor-side claims work. Legal treatment varies significantly by jurisdiction. Analytical treatment varies significantly by methodology. Both matter, but neither determines outcomes as directly as most contractors assume.
What actually determines concurrent delay outcomes in practice is a combination of factors that experienced contractor-side claims work approaches systematically. This article sets out those factors, drawing on observed patterns across live projects and settled positions.
The legal spectrum
English law, since Malmaison and clarified in Walter Lilly and De Beers, generally applies the 'apportionment on causation' approach where concurrent Employer-caused and Contractor-caused delays are demonstrated — with the Contractor entitled to extension of time for the Employer-caused delay period even where the Contractor-caused delay operates concurrently, but not entitled to associated prolongation cost.
Scottish law (following City Inn) applies a more explicit apportionment approach, dividing responsibility between concurrent causes on a case-by-case basis.
US courts (Wickwire and subsequent) generally apply time-band apportionment with case-specific variation.
Civil law jurisdictions apply their own principles, which often reduce to good-faith apportionment principles.
Middle Eastern jurisdictions typically follow either English law principles (in DIFC / ADGM) or civil-code principles depending on the applicable law. Bespoke arbitration clauses often specify the applicable approach directly.
The practical implication is that jurisdiction matters materially for concurrent delay treatment. It is the first thing to establish on any concurrent-delay claim.
The SCL Protocol position
The Society of Construction Law Delay and Disruption Protocol (2nd edition) provides a widely-referenced framework for concurrent delay treatment, generally aligned with the Malmaison approach — extension of time granted for the Employer-caused delay period, no associated prolongation cost.
The SCL Protocol is not itself law, and its application is contract-dependent. But it provides a reference point that most claims practitioners recognise, and its methodology is often adopted by DABs, arbitrators and expert witnesses as a working framework.
For contractors preparing concurrent-delay claims, aligning the analysis with the SCL Protocol approach (where jurisdiction and contract permit) usually reduces the space for methodological dispute — which shifts the dispute to the underlying facts, where the contractor's record base has the strongest influence.
What actually determines outcomes
In the concurrent-delay claims we have worked on and observed, the outcome has been driven far more by the quality of the record base and the analytical discipline than by the legal or protocol position. The reason is that concurrent-delay disputes almost always come down to factual questions — was there actually concurrency, when did each delay start and end, was each delay actually on the critical path, was mitigation attempted.
Where the contractor has a defensible programme record, disciplined notice trail, and clear cause-and-effect narrative, concurrent-delay claims tend to succeed on their factual merits regardless of jurisdictional variation in legal treatment. Where the contractor's record base is weak, the legal position rarely rescues the claim — because the factual predicates for the legal argument haven't been established.
The specific record elements that matter
Programme integrity is the single most important element. Baseline programmes maintained and updated in accordance with the contract's requirements. Progress reported honestly and consistently. Critical path integrity preserved across updates. Where these hold, concurrent-delay analysis has a defensible foundation. Where they don't — baselines drifted, critical path shifted, updates untied to progress — the analysis becomes contestable at every step.
Notice discipline on both delay events matters as much as programme discipline. Employer-caused delay events notified under the applicable clause within the time bar. Contractor-caused delay events acknowledged internally and reflected in updated programmes. Contractors that notify Employer-caused delays and quietly ignore Contractor-caused delays create record-base contradictions that opposing analysis will exploit.
Cost records supporting the delay periods matter for prolongation cost recovery — even where the legal position denies concurrent prolongation cost, the cost records establish the quantum available for whatever portion of the delay is recoverable.
Analytical method selection for concurrent delay
Windows Analysis and Time Impact Analysis are the methodologies most commonly used for concurrent delay claims. Both allow explicit identification of periods where concurrent causes operated, with defined treatment of the concurrent effect within each window.
As-Planned vs As-Built and Impacted As-Planned are less suitable for concurrent-delay analysis because they compress the delay effect into aggregate periods that obscure the concurrency. They can be used but usually require supplementary analysis to make concurrency visible.
The method selected should be documented explicitly, with the reasoning stated. Concurrent-delay claims that get rejected on methodology grounds are usually rejected because the methodology was left implicit — and implicit methodology is contestable methodology.
The practical position for contractors
For contractors managing potential concurrent-delay situations on live projects, the practical position is: preserve the record base, notify explicitly, choose the methodology deliberately, and align with the applicable jurisdictional treatment (rather than fighting it).
The legal position on concurrent delay is important but rarely decisive. The record base is decisive. Contractors that maintain disciplined records across their live projects have the ability to make defensible concurrent-delay claims when the situation arises. Contractors that don't will find their concurrent-delay position determined by the record they didn't keep — regardless of what the legal position says.
This is another area where the shared-capability model produces particular value — because programme discipline, notice discipline and record consistency across every project on the portfolio determines whether concurrent-delay claims are recoverable when they arise. Contractors running these workstreams to consistent standards across every project have a materially better claims position than contractors running them project-by-project.