Extension of Time: Managing Delay Claims Effectively

8 May 2026 · 5 min read · Contract Administration

Approximately 70% of UK construction projects experience some form of delay. Not all delays entitle the contractor to an extension of time (EOT), and not all delays result in financial loss to the employer. Managing delay claims effectively — whether you're the contractor claiming or the employer defending — requires understanding the contractual framework, the evidential requirements, and the delay analysis methodology.

Notice: The First Casualty

Under both JCT and NEC, the contractor must give notice of a delaying event within a specified timeframe. The requirements differ:

• JCT — notice "as soon as practicable" and in any event within the period specified in the contract particulars (typically 8–14 days from becoming aware of the delay). Failure to give notice does not necessarily bar the claim (unlike NEC), but it weakens the contractor's position and may affect the assessment.
• NEC — notice of a compensation event within 8 weeks of becoming aware of the event. If the contractor misses this deadline, the claim is barred — NEC's strict notification requirement is unforgiving and is one of the most litigated aspects of the contract.

Notice is not a formality. It's the trigger for the contract administrator's assessment process, the mechanism for the employer to plan around the delay, and the evidential foundation for the eventual claim. Late or vague notices — "we may be delayed by weather" rather than naming the event, the likely delay, and the cause — are routinely challenged and often rejected.

Relevant Events vs Relevant Matters

Under JCT, there's a critical distinction between two categories:

• Relevant Events — entitle the contractor to an extension of time (protection against liquidated damages). Examples: force majeure, exceptionally adverse weather, client variations, delays by nominated subcontractors, strikes.
• Relevant Matters — entitle the contractor to loss and expense (financial compensation). Examples: variations, disruption from instructions, late information, suspension by the employer.

Some events are both — a variation may cause delay (Relevant Event for EOT) and additional cost (Relevant Matter for loss and expense). But some events are one and not the other: exceptionally adverse weather gives EOT but not loss and expense. This distinction is the most common source of dispute in delay claims.

Concurrent Delay: The Battleground

Concurrent delay occurs when two causes of delay overlap — one the employer's responsibility and one the contractor's. The classic scenario: a variation instruction is issued during a period when the contractor is already in culpable delay.

The approaches to concurrency are:

• Extension of time apportionment — the contractor gets EOT for the employer-caused portion only. This is the dominant approach in UK law following Walter Lilly v Mackay (2012) and subsequent cases.
• Prevention principle — the employer cannot benefit from their own delay to reduce the contractor's EOT entitlement. Applied in some cases but limited by the contract's extension of time mechanism.
• Malmaison approach — if the employer-caused delay is on the critical path, the contractor gets EOT regardless of concurrent contractor delay. Controversial and not universally applied.

Delay Analysis Methods

The Society of Construction Law Delay and Disruption Protocol identifies several methods for analysing delay:

• Time impact analysis (prospective) — inserts the delay event into the programme and measures the impact on completion. The most widely accepted method.
• As-planned vs as-built (retrospective) — compares the planned programme to what actually happened and identifies where the divergences occurred.
• Windows analysis — divides the project into time windows and analyses delay within each window. Useful for complex, multi-event delays.
• But-for analysis — "but for this event, would the project have completed on time?" Simple but often inconclusive in multi-causal scenarios.

Practical Steps for Contractors

1. Maintain a contemporaneous programme — update monthly. A stale programme is useless for delay analysis. If the programme isn't being maintained, the claim is already weakened.
2. Serve notice immediately — do not wait to assess the full impact. Give a preliminary notice naming the event, then follow up with detailed particulars. JCT and NEC both permit this approach.
3. Keep daily site records — weather, workforce numbers, deliveries, instructions received, progress photographs. These are the raw material for any delay claim and are impossible to recreate after the fact.
4. Identify the critical path — a delay claim is only strong if the delaying event affected the critical path. A non-critical delay does not entitle EOT.
5. Quantify separately for time and money — EOT and loss/expense are separate claims with separate tests. Don't assume that one follows from the other.

Practical Steps for Employers

1. Respond to notices promptly — JCT requires the contract administrator to respond to an EOT claim within a reasonable time (often 2–8 weeks depending on contract). Failure to respond can amount to a breach.
2. Challenge vague claims — a notice that says "we'll be delayed" without identifying the event, the cause, and the estimated impact is not sufficient. Require particulars before assessing.
3. Check for concurrency — is the contractor in culpable delay? If so, the EOT analysis must address concurrency explicitly.
4. Maintain your own records — the employer's QS should keep a parallel record of site progress, instructions issued, and information provided. This is essential for defending claims.
5. Don't withhold unreasonably — if the contractor is entitled to EOT, grant it. Withholding to maintain leverage on liquidated damages risks a dispute that will cost more than the time is worth.

Sources: JCT 2024 suite (extension of time and loss and expense provisions); NEC4 Engineering and Construction Contract (compensation events); Society of Construction Law Delay and Disruption Protocol (2nd edition, 2017); Walter Lilly v Mackay [2012] EWHC 1773; Henry Boot v Malmaison [1999]; RICS delay and disruption guidance; NorthEight dispute experience. This article is for general guidance only and does not constitute legal advice.