FIDIC Engineer's Determination (Clause 3.5): What It Means and What to Do Next
Six weeks after the Contractor submitted detailed particulars for an unforeseen ground conditions claim, an email arrives from the Engineer. Subject line: "Determination — Claim Ref UGC-04." It runs to four short paragraphs, grants nine of the forty-two days claimed, and gives almost no reasoning for the rest. The Project Manager reads it twice, then asks the only question that matters: what exactly just happened, and what happens if the Contractor doesn't agree with it?
What an Engineer's Determination Actually Is
Under the FIDIC 1999 Red Book, Sub-Clause 3.5, and the FIDIC 2017 Second Edition, Sub-Clause 3.7, whenever the Conditions require the Engineer to agree or determine a matter — most often the outcome of a claim submitted under Clause 20 — the Engineer has a specific duty. It is not simply "decide what the Employer wants." The Engineer must consult with each Party in an endeavour to reach agreement, and only if agreement is not achieved, make a fair determination in accordance with the Contract, taking due regard of all relevant circumstances.
That wording matters. The Engineer is typically appointed and paid by the Employer, an obvious source of tension. FIDIC's answer is to impose an independent, quasi-judicial duty of fairness on the determination itself — the Engineer is not an advocate for either side, but a neutral decision-maker acting within the Contract. In practice that neutrality varies, which is exactly why the challenge mechanism later in this guide exists.
Key Takeaway: A determination is the Engineer's own decision on a claim, made under Sub-Clause 3.5 (1999) or 3.7 (2017). The Engineer must first try to get the Parties to agree, and only decide unilaterally — fairly, and grounded in the Contract — if agreement fails.
The Two Steps: Consultation, Then Determination
The sequence is easy to miss because it usually happens quietly, inside routine correspondence rather than as a labelled procedure. First, the Engineer consults both Parties and tries to broker agreement — through site meetings, letters, or informal discussion around the submitted particulars. Only if that fails does the Engineer move to a unilateral determination.
This is why the particulars submitted earlier carry more weight than they appear to at the time. A submission that reads as a self-contained case — narrative, contractual basis, programme analysis, and cost substantiation all present — gives the Engineer little room to issue a thin, unreasoned determination without it looking exactly like what it is. A submission with gaps invites an equally gappy response, and that response is easier for the Engineer to defend later.
Key Takeaway: The Engineer must attempt agreement before determining unilaterally. The strength of the Contractor's original particulars directly shapes how defensible — or attackable — the resulting determination turns out to be.
How Long Does the Engineer Have to Decide?
Under FIDIC 1999, Sub-Clause 3.5 sets no explicit timeframe for the determination at all — the clause is simply silent on timing. In practice this silence has caused real frustration on 1999-form projects, where a determination can sit unresolved for months with the Contractor unsure whether to chase it or simply wait.
FIDIC 2017, Sub-Clause 3.7, replaces that vagueness with a more structured, time-limited framework, built specifically to stop a claim sitting indefinitely. The exact figure can still be amended in the Particular Conditions of a specific contract, so the safe practice is always to check the contract's own wording rather than assume either the 1999 or 2017 default applies without confirming it.
If the Engineer does go quiet on a 1999-style contract, a polite written chase is worth sending regardless — the clause's silence on timing is not the same as a licence to leave a claim unanswered indefinitely. It keeps pressure on, and it creates a dated paper trail showing the Contractor did not simply let the matter drop.
Key Takeaway: FIDIC 1999 sets no explicit timeframe for a determination at all; FIDIC 2017 replaces that silence with defined time limits. Confirm the exact figure in the Particular Conditions of the specific contract — do not assume a default applies.
What a Valid Determination Must Contain
A determination is not just a number in an email. To be valid, it must meet a few specific requirements that are easy to check and worth checking every time one arrives.
- Given to both Parties. The Engineer must notify both the Contractor and the Employer of the determination, not just the party asking for it. A determination shared with only one side is a red flag on its own.
- Supported by particulars. The notice of determination must come with supporting reasoning, not a bare figure. If the Engineer grants nine of forty-two claimed days with no explanation for the other thirty-three, that silence is itself a weakness worth challenging.
- Fair, and grounded in the Contract. The determination must be made in accordance with the Contract, taking due regard of all relevant circumstances — not shaped by commercial pressure from the Employer or a desire to keep both sides equally unhappy.
A determination that fails any of these three tests is weaker than it looks on first read, and that weakness is exactly what a well-drafted challenge should point at.
Key Takeaway: A valid determination goes to both Parties, comes with supporting particulars, and is fairly grounded in the Contract. A one-line figure with no reasoning fails the test — and is worth challenging on that basis alone.
If the Contractor Disagrees With the Determination
This is the point that usually brings a reader to this guide in the first place, and the two FIDIC editions handle it very differently.
Under FIDIC 2017, Sub-Clause 3.7 attaches a hard deadline directly to the determination itself: if either Party is dissatisfied, it must serve a Notice of Dissatisfaction within 28 days. Miss that window and the determination becomes final and binding — the merits are closed permanently, with no route back to argue them in arbitration. This guide does not repeat that letter's full template here; see the site's Notice of Dissatisfaction guide for exactly what it must say and a copy-and-adapt version.
Under FIDIC 1999, there is no equivalent 28-day guillotine on the determination. Disagreement is pursued instead by referring the dispute to the Dispute Adjudication Board under Sub-Clause 20.4 — no single hard deadline forces the Contractor's hand the way the 2017 NOD mechanism does, but that does not make delay free. Sitting on a disagreement for months can still be used against the Contractor later, on the basis its conduct looked like acceptance. The safe practice under either edition is the same: put the disagreement in writing, promptly.
Key Takeaway: Under FIDIC 2017, a Notice of Dissatisfaction is due within 28 days of the determination or it becomes final and binding. Under FIDIC 1999, challenge goes through a DAB referral with no matching guillotine — but silence still carries risk either way.
Comply Now, Argue Later
The part that surprises teams who have not been through this before: a determination takes effect immediately, whether or not the Contractor agrees with it. Both editions require each Party to give effect to the Engineer's determination unless and until it is revised through the Clause 20 dispute process. Treating a bad determination as void, and simply proceeding as if it never happened, is not an option available to either side.
In practice this means the Contractor keeps working to the certified programme and amounts while the challenge runs separately. It also means the underlying entitlement is not necessarily lost just because one determination went against it — a claim under-supported the first time can often be re-presented with better evidence later, if the record is still open. Comply with what has been decided, and keep building the case for what has not.
Key Takeaway: A determination is binding the moment it is given, even if disputed. Comply with it while the challenge proceeds separately — non-compliance is a different, and separately risky, breach.
Common Mistakes Around Determinations
- Treating an unfavourable determination as final without checking. It usually isn't — check the applicable challenge deadline first, before assuming the matter is closed.
- Missing the 28-day NOD window under 2017. The single most expensive mistake on this list — a bad determination becomes permanently unchallengeable.
- Assuming Engineer silence past the time limit is a win. It usually is not. The contract's own escalation mechanics govern what happens next, not a default assumption that no answer means yes.
- Submitting thin particulars, then being surprised by a thin determination. An under-supported claim gives the Engineer little to engage with — and little for the Contractor to attack in return.
- Refusing to comply while disputing. The determination is binding until revised; withholding compliance turns a defensible disagreement into a separate breach.
- Confusing a determination with a DAB decision. They are different bodies with different challenge routes — see the FAQ below for how they actually relate.
Most come from treating the determination as the end of the conversation rather than one step in a longer process with its own rules and its own clock.
Key Takeaway: The costliest mistake is missing the 2017 NOD deadline. The rest come from treating a determination as final when it usually isn't, or as optional when it never is.
Frequently Asked Questions
What's the difference between an Engineer's determination and a DAB decision?
An Engineer's determination is the Engineer's own decision on a claim or matter under Sub-Clause 3.5 (1999) or 3.7 (2017) — made by the person administering the contract day to day. A Dispute Adjudication Board decision comes from an independent, contractually appointed board under Clause 20, and is only reached if a dispute is referred to it, typically after a Party has disagreed with the Engineer's determination and pursued the matter further. The determination usually comes first; the DAB decision, if it happens, comes later.
How long does the Engineer have to make a determination?
FIDIC 1999 Sub-Clause 3.5 sets no explicit timeframe at all — it is simply silent on timing, which in practice has meant determinations sitting unresolved for months on some projects. FIDIC 2017 Sub-Clause 3.7 replaces that silence with defined time limits so a claim cannot sit indefinitely, though the exact figure can be amended in the Particular Conditions. Always check the contract's own wording before assuming either default applies.
What happens if I disagree with the Engineer's determination?
Under FIDIC 2017 Sub-Clause 3.7, a Party that disagrees must serve a Notice of Dissatisfaction within 28 days of the determination — miss that window and the determination becomes final and binding, closing the door on the merits permanently. Under FIDIC 1999, there is no equivalent 28-day guillotine on the determination itself; disagreement is pursued by referring the dispute to the Dispute Adjudication Board under Sub-Clause 20.4. Either way, the safe practice is to record disagreement in writing promptly rather than let it sit.
Do I have to comply with a determination I disagree with?
Yes. Under Sub-Clause 3.5 (1999) and its 2017 equivalent, each Party must give effect to the Engineer's determination unless and until it is revised through the Clause 20 dispute process. Disagreeing with a determination does not excuse the Contractor from acting on it in the meantime — comply now, and pursue the challenge separately.
Does the Engineer have to give reasons for a determination?
Yes. A valid determination must be given to both Parties with supporting particulars, and it must be made fairly, in accordance with the Contract, taking due regard of all relevant circumstances — not just a number with no explanation. A determination that rejects or reduces a claim without reasoning is weaker, and worth challenging on that basis alone.
Authoritative Sources
This guide reflects the FIDIC Conditions of Contract and established construction-law authority. For the primary materials, see:
- FIDIC Conditions of Contract — the official contract suite published by the International Federation of Consulting Engineers, which sets out the Engineer's role and the Sub-Clause 3.5 / 3.7 determination procedure.
- SCL Delay and Disruption Protocol — the Society of Construction Law's widely used guidance on how delay and disruption claims are assessed and determined in practice.
About the Author
Muhammad M. Jiwani is a Project Director with 15 years' experience on major infrastructure and energy projects administered under FIDIC contracts. He writes from first-hand experience serving notices and managing contractual claims on live projects.