Investigating Concurrent Delay in Construction Contracts
Concurrent delay is essentially a causation question answered through the contract. The result depends on whether two events were each an effective cause of delay to completion, how the extension of time clause allocates that risk, whether notice conditions were met, and whether the claim is for time, liquidated damages or prolongation cost.
The practical lesson from the authorities is that a recognised delay methodology does not substitute for proof of what work was critical, when it was delayed and why.
The 2022 decision in Thomas Barnes & Sons plc v Blackburn with Darwen Borough Council is a useful focal point. The Technology and Construction Court treated delayed roof coverings and employer-risk steelwork remediation as concurrent causes even though they did not start together. The court granted time for the employer-risk delay but confined compensation to the period that was not concurrent. Read with Australian, UK and overseas authorities, the decision supports a disciplined approach: identify the operative contractual rule first, then test causation period by period against the contemporaneous record.
The core proposition
A delay event is legally relevant only if it affects completion or another contractual milestone. Two events may occur in the same period without being concurrent in the legal sense. If one event affects an activity with float, or affects a non-critical workstream, it does not delay completion and cannot be a concurrent cause of completion delay.
The Society of Construction Law Delay and Disruption Protocol defines true concurrency narrowly. An employer-risk event and a contractor-risk event must occur at the same time, their effects must be felt at the same time, and each must be an effective cause of delay to completion. The Protocol also recognises the more common situation in which events begin at different times but their delaying effects overlap. The distinction matters because courts have differed on whether the first event to consume the available float prevents the later event from being causative.
The Protocol is influential guidance, not a statement of law and not a contractual term unless the parties make it one. Its recommended outcome is commonly summarised as time but no money: contractor delay should not reduce an extension of time due for an employer-risk event, but the contractor should recover compensation only to the extent it proves that employer delay caused additional loss beyond loss that would have occurred in any event. That formulation is a useful starting point, but the contract and governing law remain controlling.
Five questions in considering concurrent delay
Definition. Were there two effective causes of delay to the same completion date or milestone, or only two events happening on the project at the same time?
Entitlement to time. Does the extension of time clause grant time for an employer-risk event despite concurrent contractor delay, require apportionment, or expressly exclude concurrent periods?
Entitlement to money. Can the contractor prove that the employer-risk event caused the claimed prolongation cost, rather than cost that contractor delay would have caused in any event?
Liquidated damages. Does the adjusted completion date move, and does the contract permit liquidated damages during a period for which the employer also caused delay?
Procedure. Were notice, programme, particulars, mitigation and assessment requirements satisfied, and did the superintendent or contract administrator properly exercise any discretionary power?
Thomas Barnes and the effective cause approach
Blackburn with Darwen Borough Council engaged Thomas Barnes & Sons plc to construct a bus station. The works were delayed by two workstreams relevant to the hub finishes. Deflection in structural steelwork required investigation and remediation for which the Council bore responsibility. Thomas Barnes was responsible for delay to the roof coverings. Both workstreams had to be completed before the finishes could meaningfully proceed.
The parties' delay experts used different recognised methods. The contractor's expert relied principally on an as-planned versus as-built windows analysis. The Council's expert combined time-slice windows and time impact analysis. The court did not treat the choice of method as determinative. It examined the logic of the work, the evidence of what was required before finishes could start, and the actual effect of each delayed workstream.
The contractor argued, in substance, that the earlier steelwork problem created float in the roof-covering activity, so the later roof delay could not independently delay completion. The court rejected that result on the facts. It found that both the steelwork remediation and the roof coverings were critical prerequisites to the hub finishes and were each causing delay during the overlapping period. Concurrency therefore did not require identical commencement dates.
The financial outcome illustrates why time, and money must be analysed separately. Thomas Barnes received an extension of time for the employer-risk steelwork delay, but its prolongation recovery was limited to the non-concurrent part of that delay. The case does not establish a universal rule that every overlap produces an extension of time without compensation. It applies the effective cause analysis to the contract and facts before the court.
The Australian position
Australia has no single appellate rule that resolves every concurrent-delay dispute. The authorities are strongest on causation, contractual construction, the prevention principle, time bars and the administration of extension powers. They make it unsafe to import an English formulation without first reading the governing clause.
Causation and delay methodology
White Constructions Pty Ltd v PBS Holdings Pty Ltd concerned alleged delay caused by defective sewer design for a subdivision. Hammerschlag J rejected both parties' preferred delay analyses and acted on the assistance of a court-appointed programming expert. The judgment emphasises that the court must decide factual and legal causation from the evidence. Inclusion of a method in the SCL Protocol does not give the method legal standing, and omission from the Protocol does not disqualify an otherwise logical method. The claim failed because the plaintiff did not prove that the alleged breach caused the claimed period of delay. The appeal was dismissed in White Constructions Pty Ltd v PBS Holdings Pty Ltd [2020] NSWCA 277, although the appellate issues were not a general endorsement or rejection of a particular forensic delay method.
Alstom Ltd v Yokogawa Australia Pty Ltd (No 7) provides a useful contrast. In a complex power-station dispute, Bleby J undertook detailed scrutiny of competing programme analyses, their acceptance within the profession and their fit with the available records. The case shows that a recognised technique may assist, but only if its inputs, logic and treatment of the actual work are reliable. Together, Alstom and White Constructions caution against methodology-first advocacy.
Australian Development Corporation Pty Ltd v White Constructions (ACT) Pty Ltd is often cited for a first-in-time approach. A qualifying event did not produce an extension where a contractor-risk event was already causing critical delay and continued beyond the qualifying event. The later event did not change the completion outcome. This remains a powerful causation argument, but Thomas Barnes shows that a court may find two effective causes where both workstreams were necessary to release the same successor work, despite different start dates.
Prevention time bars and extension powers
Gaymark Investments Pty Ltd v Walter Construction Group Ltd is associated with the proposition that a principal may lose liquidated damages where its own prevention delays completion and the contract have no effective mechanism for moving the completion date. The decision is controversial and should not be treated as allowing a contractor to disregard notice provisions generally.
Later Australian authorities place greater weight on the bargain expressed in the contract. Peninsula Balmain Pty Ltd v Abigroup Contractors Pty Ltd and Spiers Earthworks Pty Ltd v Landtec Projects Corporation Pty Ltd (No 2) show that the existence and exercise of an extension mechanism, including a superintendent's power to extend time, can prevent time becoming at large. The consequence of a missed notice, and whether a unilateral extension power must be exercised, depend on the wording, the administrator's duties and the facts. Probuild Constructions (Aust) Pty Ltd v DDI Group Pty Ltd further illustrates the importance of administering a unilateral extension power when principal-caused delay and liquidated damages are in issue.
For contract managers, the practical point is direct. A concurrency assessment cannot be separated from the notice regime and the decision-maker's powers. A substantively credible delay case may still fail if the contractual condition precedent is not met. Conversely, a principal may compromise its liquidated-damages position if a contractual discretion intended to preserve the completion regime is ignored or exercised for an improper purpose.
The law in England and Wales
English decisions supply much of the vocabulary used in international delay disputes, but they do not yield a rule detached from the contract. The main themes are effective causation, the distinction between time and money, and freedom to allocate concurrent-delay risk expressly.
Effective causes and the first in time debate
Royal Brompton Hospital NHS Trust v Hammond explained that concurrent delay requires two causes operating so that each is effective in delaying completion. Adyard Abu Dhabi v SD Marine Services adopted a working definition of causes of approximately equal causative potency and stressed that both events must in fact delay progress, with their effects felt at the same time. On its facts, an earlier contractor delay meant later buyer events did not cause additional completion delay. That reasoning underpins the first-in-time argument.
The Malmaison approach, developed from Henry Boot Construction UK Ltd v Malmaison Hotel Manchester Ltd and examined in Walter Lilly & Co Ltd v Mackay, is commonly understood to permit a full extension of time where an employer-risk event is an effective cause of completion delay even though contractor delay is also effective. It does not follow that the contractor receives prolongation cost for the same period. Recovery of loss still requires proof that the compensable event caused that loss.
The Malmaison principle and parallel delay
The Malmaison principle comes from Henry Boot Construction UK Ltd v Malmaison Hotel Manchester Ltd. Where employer-risk and contractor-risk delays both cause delays to completion, the contractor gets time for the employer-risk event, even though it was also in delay. Walter Lilly & Co Ltd v Mackay later appliedthat approach to an unamended JCT extension of time clause.
Parallel delay is not the same as concurrency. Separate delay streams may run together, but they matteronly if each independently delays the same completion date or milestone. A non-critical delay, or one absorbed by float, does not become concurrent just because it overlaps in time.
The practical result is time, not money. The Relevant Event moves the completion date and usually defeats liquidated damages for that period. Prolongation costs still require proof that the employer-risk event caused the loss, excluding costs driven by the contractor’s own parallel delay. That is the familiar “time but no money” outcome.
This is significant in Thomas Barnes because it did not allow chronological priority to displace the factual inquiry. Both delayed items were necessary predecessors to the hub finishes. The court treated them as concurrent during the overlapping period, notwithstanding the continuing employer delay before and after the contractor delay. The decision therefore supports an effects-based analysis rather than a mechanical comparison of event start dates.
Express allocation and the prevention principle
North Midland Building Ltd v Cyden Homes Ltd confirms that sophisticated parties may allocate concurrent-delay risk expressly. The amended JCT clause provided that an employer-risk event would not be taken into account to the extent it was concurrent with contractor delay. The Court of Appeal enforced that allocation and rejected the argument that the prevention principle invalidated it. The contractor was also exposed to liquidated damages under the agreed regime.
The drafting consequence is important. General references to prevention or fairness should not be assumed to override clear concurrent-delay wording. If the parties intend time but no money, denial of time during concurrency, or apportionment, the clause should say so and should align the extension, loss and expense, liquidated damages and notice provisions.
Evidence and expert analysis
The cases do not reject expert delay evidence. They reject analysis that outruns its factual foundation. A court or tribunal needs a transparent bridge from the contractual event to the affected activity, from that activity to the critical path, and from the critical-path movement to the days and cost claimed.
What a persuasive analysis should show
The contractual completion date and every valid adjustment to it, including the legal basis for each adjustment.
The contemporaneous programme logic, updates and actual progress, including changes to the critical path and the use or loss of float.
The date, duration and responsibility classification of each alleged delay event.
The activity or Workfront actually affected, the predecessor and successor logic, and why the event moved completion or a milestone.
A period-by-period test of alleged concurrency, showing whether each event independently remained an effective cause in the relevant window.
The counterfactual outcome without the employer-risk event and, separately, without the contractor-risk event.
For money claims, the incremental cost caused by the compensable event, with contractor-caused and neutral cost removed or explained.
A label such as windows analysis, time impact analysis or as-planned versus as-built is not enough. The chosen method must suit the available records and the question the tribunal must decide.
Prospective analysis methodologies may be appropriate for contemporaneous administration, whereas retrospective methods are likely required after completion. In either setting, unexplained changes to logic, calendars, constraints, progress data or critical-path selection will weaken the opinion.
Contract managers should preserve the evidence before a dispute crystallises. Daily reports should identify work prevented, not simply record that an issue existed. Programme updates should use consistent status dates and explain logic changes. Notices should link the event to the affected activities and reserve the position as its impact develops. Meeting minutes, design registers, requests for information, access records, photographs, labour records and cost codes should be capable of being reconciled with the programme.
Drafting and administration priorities
Concurrent delay is best managed before the claim. The contract should state the intended consequence, and project controls should generate the evidence needed to apply that rule. However, they rarely do. Ideally, concurrency clauses should:
Define concurrent delay by reference to effective critical delay, rather than the mere coexistence of events.
State whether concurrency gives time, gives neither time nor money, or requires apportionment, and specify any period-by-period assessment.
Align the extension of time clause with liquidated damages, loss and expense, prevention, mitigation and acceleration provisions.
State how float is treated and whether ownership of float changes once an earlier event consumes it.
·Specify notice conditions, the information required as impacts develop, and the consequences of non-compliance.
Preserve a workable power to extend time for principal-caused delay and state who may exercise it and on what basis.
Administer the clause while the facts are fresh
Require an accepted baseline programme with logic, calendars, resources where relevant, and a clear critical path.
Update the programme regularly and record why logic, sequencing, constraints and completion forecasts changed.
Assess extension claims within the contractual timeframe and give reasons that identify the event, affected activities, critical impact and concurrent periods.
Separate the time decision from the compensation decision. A grant of time is not an admission that all prolongation cost is recoverable.
When asserting concurrency, identify the contractor-risk event and prove its independent critical effect. General references to slow progress are insufficient.
If expert evidence is likely, instruct the expert early enough to test the records, but maintain the expert's independence and preserve factual witness evidence.
“Thomas Barnes is best understood as an evidence-led application of effective causation. It does not abolish the first-in-time argument, and it does not create a universal rule for compensation. It demonstrates that a later contractor event may still be concurrent where both workstreams are critical prerequisites to the same successor work and both are in fact delaying completion during the same period.
For Australian practitioners, resist statements of a single common-law concurrency rule. Start with the clause and test each event against the critical path and contemporaneous evidence. Treat time, liquidated damages and prolongation cost as distinct questions. Administer notice and extension powers so the contractual completion regime remains workable.”
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Examining concurrent delay in construction contracts with guidance on delay expert witness evidence, forensic delay analysis and managing concurrent delay disputes in Australia.