Citable answer: An extension of time (EOT) moves the contractual Time for Completion when a qualifying event delays the works, protecting the contractor from liquidated damages. Under FIDIC the entitlement lives in Sub-Clause 8.4 (1999) or 8.5 (2017) — but it is only protected if the contractor serves notice within 28 days under the claims procedure (Clause 20.1 in 1999, Sub-Clause 20.2.1 in 2017). Miss that notice and the time is not extended.
An extension of time is one of the most valuable, and most frequently lost, entitlements on a construction project. It is the mechanism that keeps a contractor's completion date fair when something outside its control pushes the programme out — and it is the difference between an excused delay and a daily liquidated-damages deduction. The entitlement is real. What teams lose is the procedure that protects it.
What an extension of time actually does
When a project is delayed, two questions follow. Is the contractor liable for that delay, in the form of liquidated (delay) damages? And is the contractor entitled to more time to finish? An EOT answers the second. A valid extension moves the Time for Completion to a later date, so the contractor is measured against a realistic target rather than the original one — and so the employer cannot levy delay damages for a period the contractor was not responsible for.
Under FIDIC, the grant of an EOT is not automatic. The delay has to arise from a qualifying cause, and the contractor has to claim it correctly and in time.
The grounds: Sub-Clause 8.4 (1999) and 8.5 (2017)
In the FIDIC 1999 Red Book, the right to claim an extension sits in Sub-Clause 8.4. In the 2017 Second Edition it is Sub-Clause 8.5. The qualifying grounds are broadly consistent across both, and typically include: a Variation; a cause of delay giving an entitlement under another sub-clause; exceptionally adverse climatic conditions; unforeseeable shortages of personnel or goods caused by epidemic or governmental action; and any delay, impediment or prevention caused by or attributable to the Employer or the Employer's Personnel.
The 2017 edition tightened the process considerably. It made the claims machinery more prescriptive and symmetrical between Employer and Contractor, and — importantly — it addressed concurrent delay directly for the first time, of which more below.
The procedure is where entitlement is won or lost
This is the part that catches good teams. Having a valid ground for an EOT is not the same as keeping it. FIDIC ties the entitlement to a strict notice procedure with a hard deadline.
Under the 1999 Red Book, Clause 20.1 requires the contractor to give notice of a claim not later than 28 days after it became aware, or should have become aware, of the event or circumstance. If it fails to, "the Time for Completion shall not be extended, the Contractor shall not be entitled to additional payment, and the Employer shall be discharged from all liability in connection with the claim." That is a true condition precedent — a time-bar. (We cover the mechanics of that 28-day clock in detail in Clause 20.1, plainly.)
Under the 2017 Second Edition, the equivalent notice obligation is Sub-Clause 20.2.1, again 28 days, with the same discharging consequence for a late notice. The 2017 edition then adds a second clock: under Sub-Clause 20.2.4 the claiming party must submit a fully detailed claim within 84 days of becoming aware of the event (or another period agreed with the Engineer). So the contractor faces two deadlines, not one — the notice, then the substantiation.
The practical reality is brutal in its simplicity: the contractor can have an unanswerable EOT entitlement and still recover nothing, purely because the 28-day notice was never served. The entitlement was never tested on its merits. It was lost on the calendar.
When does the 28-day clock start?
A recurring question is whether the contractor must wait until delay has actually occurred before notifying. Following Akenhead J's decision in Obrascon Huarte Lain SA v Attorney General for Gibraltar [2014] EWHC 1028 (TCC), the generally accepted position under the FIDIC wording is that the contractor can give notice either when the works will be delayed (prospective delay) or once the delay has begun to be incurred (retrospective delay). The "is or will be delayed" language gives some latitude — but it is no reason to wait. The safe discipline is to notify early, the moment a delaying event is identified, and refine the detail later.
Concurrent delay: the issue that decides who pays
Concurrent delay — where an Employer-risk event and a Contractor-risk event each cause delay over the same period — is one of the most contested areas in construction claims, because it determines whether the contractor gets time, money, both, or neither.
The widely followed English-law starting point is the "Malmaison" approach, from Henry Boot Construction (UK) Ltd v Malmaison Hotel (Manchester) Ltd (1999) 70 Con LR 32: where two concurrent causes of delay operate, one of which would entitle the contractor to an EOT, the contractor is generally entitled to the extension of time (though not necessarily to the associated prolongation costs). This approach is reflected in the Society of Construction Law Delay and Disruption Protocol (2nd edition, February 2017) at sections 10.12–10.16, the leading industry guidance on delay analysis, float and concurrency.
But the parties can change that allocation by agreement. In North Midland Building Ltd v Cyden Homes Ltd [2018] EWCA Civ 1744, the Court of Appeal confirmed that a clause expressly making concurrent delay non-qualifying — effectively contracting out of the "prevention principle" — is enforceable. FIDIC 2017 takes a related route: Sub-Clause 8.5 says that where a delay caused by the Employer is concurrent with a Contractor delay, entitlement is to be assessed "in accordance with the rules and procedures stated in the Special Provisions." In other words, FIDIC 2017 hands the concurrency rule to the project-specific drafting — so the answer for your project is in your amended conditions, not the standard form.
The lesson: do not assume the standard position applies. Read what your contract actually says about concurrency, because it may have been changed.
Float, the programme, and the contractual chain
An EOT argument is, at bottom, a programme argument. Whether an event causes critical delay depends on the critical path and the available float in your schedule — which is exactly why the SCL Protocol spends so much of its length on methods of delay analysis. A delay to an activity with ample float may not move completion at all; a delay to a critical activity moves it day for day.
This is the connection most teams make too late. A slipping activity in your Primavera P6 or Microsoft Project file is frequently the start of a contractual obligation — the trigger for the very notice that protects the EOT. The programme and the contract are describing the same event from two angles, and the entitlement lives in connecting them quickly. (We unpack that chain in When a programme slip becomes a contractual notice, and the FIDIC-versus-NEC4 contrast in FIDIC notice vs NEC4 early warning.)
Where a contract-and-programme reasoning layer helps
Most EOT entitlements are not lost because the contractor was wrong. They are lost because the obligation — a 28-day notice tied to a specific clause — never reached the person who could act, before the window closed. The contract sat in a document-control system that stores it but does not read it. The programme sat in a planning tool that tracks activities but does not know the contract.
This is the gap Aven-AI is built to close. It reads your contract — FIDIC, NEC4, or heavily amended — extracts the notice obligations and their deadlines, ingests your P6 or MS Project programme, and warns the responsible person before a notice deadline lapses or a slip goes un-notified. When the right conditions are met it drafts the Letter or Notice, grounded in the actual clause and cited back to source. Then it stops. It is advisory only: it never sends, signs, or files anything. You review, you decide, you issue. The entitlement stays where it belongs — with the people running the project, in time to protect it.
This article is general information about construction contract practice, not legal advice. It cites the source materials so you can verify each point and take advice on your specific contract.
Sources & further reading
- FIDIC, Conditions of Contract for Construction (Red Book), 1999 and 2017 Second Edition — Sub-Clauses 8.4 / 8.5 and Clause 20.
- Society of Construction Law, Delay and Disruption Protocol, 2nd edition (February 2017), sections 10.12–10.16 — concurrency, float and methods of delay analysis: scl.org.uk
- Obrascon Huarte Lain SA v Attorney General for Gibraltar [2014] EWHC 1028 (TCC).
- Henry Boot Construction (UK) Ltd v Malmaison Hotel (Manchester) Ltd (1999) 70 Con LR 32.
- Walter Lilly & Co Ltd v Mackay [2012] EWHC 1773 (TCC).
- North Midland Building Ltd v Cyden Homes Ltd [2018] EWCA Civ 1744.
- Gowling WLG, "FIDIC: Claims for time under the 1999 / 2017 Red Book": gowlingwlg.com
- Fenwick Elliott, "Some thoughts on how the 2017 FIDIC contract deals with time": fenwickelliott.com