Variations under FIDIC Contracts: Implications for Complex Projects and Protective Tools for Contractors

In complex projects and, more generally, in international construction contracts, a change to the originally planned arrangements is anything but an exceptional occurrence. The evolution of the employer's requirements, the progressive development of the design, the coordination among a multiplicity of parties involved, and the actual conditions under which the works must be carried out may make it necessary to revisit the technical solutions adopted, the sequencing of the works, the time for completion, or even the scope of the contractual obligations themselves.

Recent experience offers a particularly clear illustration of this. The Covid-19 pandemic, disruptions to supply chains, the unavailability or significant increase in the cost of materials and labour, unforeseen regulatory developments, and unexpected conditions encountered during execution have all affected the programme and organisation of numerous projects. Circumstances not contemplated at the time the contract was entered into, or in any event difficult for the parties to control, may indeed require a revision of the manner in which the works were originally conceived.

It is precisely the frequency with which such circumstances arise that makes it particularly important to consider the contract's capacity to regulate change even before it occurs. The issue is not merely whether a given modification may be requested, but rather identifying the conditions under which it may be ordered, the persons entitled to issue the relevant instructions, the procedures to be followed, and the consequences that flow from it in terms of cost and time.

As a general matter, under FIDIC contracts changes to the works are addressed through the system of Variations, governed by Clause 13 of the principal forms of contract. This regime is one of the tools through which the FIDIC model seeks to reconcile two needs that are only apparently in conflict: on the one hand, allowing the project to be adapted to circumstances that emerge during execution and, on the other, preserving the predictability of costs, time and the responsibilities assumed by the parties.

At the same time, the existence of a dedicated contractual procedure does not mean that every additional or more onerous activity constitutes a Variation, nor that any instruction given during the works automatically entitles the contractor to additional payment. Whether a given change qualifies as a Variation depends on the Scope of Work, the allocation of design responsibility, the powers conferred on the Engineer, and compliance with the notification procedures applicable to the various communications and/or instructions.

The centrality of these issues was recently confirmed by the Judicial Committee of the Privy Council in its decision in Uniform Building Contractors Ltd v The Water and Sewerage Authority of Trinidad and Tobago, handed down on 22 January 2026, concerning a contract based on the 1999 Yellow Book. The Privy Council held that activities already comprised within the contractor's obligations and within the lump-sum price could not be classified as Variations merely because they proved more difficult or costly than expected, while at the same time reaffirming the importance of the procedures prescribed for the formulation of claims.

It is precisely in this practical dimension that the stage preceding execution of the contract becomes significant. While the standardisation of the FIDIC forms offers the parties a recognisable contractual language and a structure widely used in international practice, it does not remove the need to verify whether the form chosen, the Scope of Work, the Particular Conditions and the procedures for managing Variations are genuinely consistent with the characteristics of the project and with the contractor's own organisation.

The Choice of FIDIC Contractual Model: Red, Yellow and Silver Book

Before examining the Variations regime, it is worth clarifying that FIDIC contracts do not constitute a single, unitary model but rather a set of standard conditions drafted for different types of project. Among the forms most widely used in international practice are the Red Book, the Yellow Book and the Silver Book, whose principal distinguishing feature lies in the allocation of design responsibility and risk between employer and contractor.

All three forms were first published in 1999 and subsequently updated in the second editions of 2017, reissued with amendments in 2022. The 2017 editions introduce a more detailed regime governing communications, claims and dispute-avoidance mechanisms. In international practice, however, the 1999 editions remain widely used and, in many markets, continue to represent the principal contractual reference, while use of the 2017 editions is progressively becoming more established.

Identifying the applicable edition is therefore particularly important, since the procedures and content of individual clauses may differ significantly between editions.

As a general rule, the Red Book applies where the design of the works is prepared predominantly by the employer or by the professionals engaged by the employer. The contractor thus principally assumes the obligation to carry out the works on the basis of the design received, while the contract is administered by the Engineer. This model is normally chosen where the employer already has a sufficiently developed design and intends to retain control over it.

Under the Yellow Book, by contrast, design is entrusted predominantly to the contractor. The employer sets out in the Employer's Requirements the characteristics and performance the works must achieve, leaving it to the contractor to develop the technical solutions needed to deliver the required outcome. This model is therefore suited to projects in which the design and technological expertise of the contractor play a particularly significant role.

The Silver Book, on the other hand, is intended primarily for EPC/turnkey projects, in which the contractor assumes broader responsibility for design, procurement and construction of the works. It is generally used where the employer wishes to obtain a genuinely turnkey result, limit its own involvement in the day-to-day management of the works, and achieve greater certainty as to the final price and completion date. The wider transfer of risk, however, may be reflected in a higher price, since the contractor will tend to factor the additional risks assumed into its tender.

The choice between the Red, Yellow and Silver Books is not, therefore, of merely formal significance. It determines who is to design the works, which party bears the risks associated with the solutions adopted, and which activities may be regarded as already included in the contract price. It is precisely this choice, accordingly, that also determines whether a subsequent request from the employer can be characterised as a Variation.
 

Variations under FIDIC Contracts: Scope of Work, Design Responsibility and Change Management

Under FIDIC contracts and, more generally, in international construction contracts, whether an activity qualifies as a Variation depends first and foremost on the correct identification of the obligations originally assumed by the parties. In general terms, a Variation consists of a change to the works or contractual obligations, introduced in accordance with the procedures laid down in the contract. It may concern quantities, the technical characteristics of the works, the sequencing of construction activities, or the adoption of different design solutions.

The issue, however, is not merely whether a change has occurred, but whether the activity requested was already included within the Scope of Work, the Employer's Requirements, the technical specifications, or the contractor's functional obligations. The same request may, in fact, be characterised differently depending on the FIDIC model chosen and the resulting allocation of design responsibility. Under the 2017 editions of the Yellow Book and the Silver Book, particular importance also attaches to the fitness-for-purpose obligation, referable to the purpose of the works as set out in the Employer's Requirements.
It is precisely in this practical dimension that the main difficulties arise. In complex projects, drawings, technical specifications, the contractor's tender and the Employer's Requirements may overlap, contain gaps, or set out indications that are not fully consistent with one another. The question therefore concerns not only the identification of the prevailing document, but also the very delimitation of the obligations included in the price and of the responsibilities attributed to each party.

Equally important is identifying the person authorised to order the change. In the models that provide for an Engineer, the Engineer plays a central role in issuing instructions and evaluating Variations, although its powers may be limited by the Particular Conditions. In practice, moreover, a request may be contained in minutes of a meeting, in an e-mail, in a revised drawing, or in an instruction given during the course of the works. It therefore becomes essential to verify the source of the instruction, the form required by the contract, and whether subsequent confirmation is needed.

A Variation may affect not only the immediate cost of the additional activity, but also the programme of works, the critical path, site organisation and relations with suppliers and subcontractors. A change does not, however, automatically give rise to a right to additional payment or to an extension of the completion date. The contractor must normally demonstrate its effects and comply with the procedures prescribed for notices, claims and the Extension of Time.

In this respect, the applicable edition is of decisive importance. Under the 1999 FIDIC conditions, Sub-Clause 20.1 generally provides that the claim must be notified within 28 days of becoming aware of the event and subsequently substantiated in detail within 42 days. Under the 2017 editions, the time limit for the notice remains 28 days, while the fully detailed Claim must, as a rule, be submitted within 84 days. It is therefore not sufficient to document the additional works from a technical and accounting standpoint if the procedure required to obtain their recognition is not activated at the same time.
At the same time, the increased cost of an obligation already included within the Scope of Work does not, in itself, transform it into a Variation. Inflation, procurement difficulties, change in law and Exceptional Events are distinct mechanisms, each subject to its own specific contractual requirements.

The importance of these enquiries was recently confirmed by the decision handed down on 22 January 2026 by the Judicial Committee of the Privy Council in Uniform Building Contractors Ltd v The Water and Sewerage Authority of Trinidad and Tobago, concerning a contract based on the 1999 Yellow Book. The dispute concerned certain works which the contractor considered to be additional to those included in the lump-sum price.

The Privy Council held that obligations already expressly or impliedly included within the Scope of Work could not become Variations merely because they proved more complex or costly than originally anticipated. The decision also clarified that the Engineer cannot, through its own conduct, alter the contractual arrangement agreed by the parties or relieve them from compliance with the procedures prescribed for claims. Even had the activities been capable of qualifying as Variations, the contractor would still have had to comply with the time limits and notifications required by Sub-Clause 20.1, which was treated as a condition precedent to obtaining additional payment.

Hence the importance of the stage at which the FIDIC contract is prepared and negotiated. Before signature, the parties should verify the Scope of Work, the hierarchy among the contract documents, the powers of the Engineer, and the procedures required to obtain recognition, in terms of both cost and time, of Variations. The aim is not to eliminate every uncertainty associated with the execution of a complex project, but rather to make the legal and economic risk identifiable in advance and, as far as possible, measurable.

Conclusions

The management of Variations under FIDIC contracts cannot be addressed solely during the execution of the works, once the change has already been requested and it is necessary to determine whether it gives rise to a right to additional payment or to an extension of time. On the contrary, it requires preventive action that should begin as early as the stage of preparing the tender and negotiating the contract.

From this perspective, what matters is not only the choice between the Red, Yellow and Silver Books, but also the identification of the applicable edition, of the amendments introduced by the Particular Conditions, and of the hierarchy among the Employer's Requirements, technical specifications, drawings and the contractor's tender. It is precisely from the coordinated examination of these documents that the Scope of Work can be defined and, consequently, the boundary between obligations already included in the price and those capable of being characterised as Variations.

Equally important is the establishment of internal procedures consistent with the contract, enabling the persons authorised to issue instructions to be identified, changes to be promptly documented, and notices and claims to be submitted within the prescribed time limits.

It remains the case that no amount of preventive review can entirely eliminate the uncertainties associated with the execution of a complex project. A properly structured contract, however, together with procedures suited to the contractor's organisation and to the characteristics of the works, can significantly reduce the risk that a change will fail to be recognised as a Variation.

Fabiola Masotta
de Capoa Law Firm