FIDIC reference
Clause 13 — Variations and Adjustments
The Engineer’s power to instruct Variations and how they are valued and paid.
Applies in: Red BookYellow BookSilver Book
Clause 13 lets the Engineer instruct a Variation (change in scope, quality or sequence) before the Taking-Over Certificate. A Variation is made by instruction (13.3.1) or by request for proposal (13.3.2). It is valued using agreed rates/prices, and may also give an entitlement to EOT under 8.5. Variations are a frequent source of claims, so instructions and records must be captured.
Key points
- Instructed by the Engineer (13.3.1) or via RFP (13.3.2).
- Valued using agreed rates and prices.
- May give entitlement to EOT (8.5) and extra payment.
- Capture instructions and contemporary records.
How this works in practice
The most expensive mistake under Clause 13 is doing the work on a verbal instruction or a drawing passed over informally, then looking for a payment route afterwards. A change must be constituted as a Variation: an Engineer’s instruction or an agreed proposal. Without that, the argument shifts to proving an instruction in fact and the Employer’s benefit, which is materially harder. The second flashpoint is valuation: the parties rarely dispute that a change occurred, they dispute the applicable rates — and that turns on how carefully measurement and resource records were kept at the time.
Common traps
- Verbal site instructions with no follow-up confirmation in writing under Sub-Clause 3.5.
- Particular Conditions introduce a threshold below which a change is not paid — small Variations then accumulate into a material sum.
- No contemporaneous record of actual resources: six months later the gang composition and hours cannot be reconstructed.
Versions: 1999 → 2017 → 2022
- 1999
Clause 13 with a similar structure; value engineering existed.
- 2017
The 13.3 process (instruction vs request for proposal) and the link to 3.7 were clarified.
- 2022
No substantive change in the 2022 reprint.
Clause FAQ
Which FIDIC books use Sub-Clause 13?
The clause applies in Red Book, Yellow Book, Silver Book. Particular Conditions may change the standard risk allocation, so always check the project contract.
Must the Contractor carry out a Variation if it disagrees with the valuation?
Generally yes: an instruction to vary must be carried out, and the disagreement over price is resolved separately through the Engineer’s determination and, if needed, the DAAB. The exceptions are narrow — for example where the required goods are not readily obtainable, or the change falls outside what the contract contemplates. Refusing to comply because the price is disputed is a risky position.
When do contract rates apply and when are new rates used?
Contract rates apply by default. A new rate becomes arguable where the work differs materially in character or conditions of execution, or where a change in quantity crosses the stated thresholds and makes the original rate inappropriate. What decides it is not argument but data: a comparison of actual output and resource composition before and after the change.
Glossary terms
Related clauses
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Reference material, not legal advice. Always check your contract and the Particular Conditions.