Valuing Variations Under FIDIC: Rates, Dayworks and Fair Value Explained

Contractors celebrate winning a variation instruction and then quietly lose money on it, because the fight over whether the work is a variation is only half the battle. The other half is valuation, and FIDIC gives the Engineer a structured method for pricing changes under Clause 13. If you do not understand that method as well as the Engineer does, you will accept contract rates where new rates were justified, absorb costs that daywork would have captured, and price variations as if they cost you nothing to disrupt your programme. The valuation rules exist to protect you - but only if you invoke them.

The Valuation Hierarchy Under Clause 13

FIDIC Clause 13 sets out how variations are valued, and it works as a hierarchy rather than a free-for-all. The starting assumption is that where the varied work is of similar character and executed under similar conditions to work already priced in the contract, the existing bill rates or prices apply. This keeps the parties honest and prevents opportunistic re-pricing of routine changes. For a lot of straightforward additions and omissions, the contract rate is the right and fair answer.

The hierarchy only moves off the contract rate when the conditions that justified that rate no longer hold. If the varied work differs in character, or is carried out under materially different conditions, or the quantity change is large enough to make the original rate unreasonable, then a new rate or price becomes appropriate. This is where SME contractors routinely undersell themselves. They apply the bill rate to work that is genuinely different - executed out of sequence, in worse conditions, or at a fraction or a multiple of the original quantity - because reaching for the familiar rate feels safer than arguing for a new one.

When Contract Rates Apply and When They Do Not

The test is character and conditions, not merely description. Two activities can share a bill description and yet be entirely different work in practice. Excavating a trench in open ground at the start of the job is not the same as excavating the same trench between live services, in a congested site, months later. The first may be fairly priced by the bill rate. The second is similar in name only, and pricing it at the original rate transfers the cost of the harder conditions from the Employer to you for free.

Quantity is the other trigger that contractors forget. A significant change in the quantity of an item can render the original rate unreasonable in either direction. If a large priced quantity is drastically reduced, your fixed and time-related costs no longer spread across the volume you assumed, so the unit rate no longer recovers them. If a quantity balloons, the conditions of working may change entirely. FIDIC recognises this, and the machinery for a new rate exists precisely so that neither party is trapped by an assumption that the change has broken. The discipline is to test every instructed change against character, conditions, and quantity before defaulting to the bill.

New Rates and the Building-Up Method

When a new rate is justified, it is usually built up from the constituent costs rather than plucked from the air. The fair approach starts from any relevant contract rate as a base and adjusts it for the differing element - the harder access, the additional labour hours, the smaller batch, the extra plant standing time. Where no comparable contract rate exists at all, the new rate is built from reasonable cost of labour, plant, and materials plus appropriate allowances for overhead and profit consistent with the rest of the contract pricing.

The practical skill is documenting the build-up so it is defensible. An Engineer confronted with a bare number will discount it; an Engineer shown a transparent build-up from resources and rates that mirror the contract's own pricing logic has little room to argue. This is also where a plain-English grasp of what actually counts as a change protects you - understanding the boundary between an instruction, a variation, and a mere clarification stops you from pricing changes you were entitled to reject or from giving away ones you should have valued. Our guide on the difference between a change order, a variation and a compensation event sets out that boundary.

Daywork - The Basis Contractors Underuse

Daywork is the valuation basis for work that cannot sensibly be measured and rated - typically minor, incidental, or highly variable work where the effort is better captured by recording actual resources than by pricing a defined quantity. Under FIDIC, where the contract includes a daywork schedule, the Contractor is generally paid on the basis of recorded labour hours, plant, and materials at the daywork rates, plus the contractual additions. It is the right tool when the scope is genuinely open-ended or too fiddly to measure.

The reason contractors lose money on daywork is administrative, not commercial. Daywork stands or falls on records. If your foreman does not submit contemporaneous daywork sheets - identifying the operatives, the hours, the plant, and the materials, and getting them signed by the Engineer's representative as the work happens - you will be unable to substantiate the claim later. Unsigned, reconstructed daywork is the easiest thing for an Engineer to reject. The rate is only as good as the sheet behind it, and the sheet has to be captured on the day, not assembled from memory at month end.

How SME Contractors Lose Money on Variations

The pattern is consistent across the SME contractors we see. They price variations as bare cost of the added work and forget the ripple effects - the disruption to the sequence, the time-related preliminaries the change drags along, the lost productivity on surrounding activities. They accept a contract rate for work that has moved into materially worse conditions. They fail to record daywork properly. And they submit round-number lump sums that invite negotiation downward rather than transparent build-ups that hold their value.

There is also a quieter loss: agreeing the money without addressing the time. A variation that adds work to the critical path may carry an entitlement to an extension of time and the associated prolongation cost, but only if you flag it when the variation is instructed and valued. Settling the direct cost of a change while staying silent on its programme impact is a standard way to give away the larger part of the claim. The cleanest protection is to fix the valuation basis and the time position at the moment of instruction, before positions harden.

Fair Valuation and Getting Ahead of the Dispute

Fair value is the thread running through the whole clause. Even where the mechanical rules do not give a clean answer, the Engineer is required to determine a valuation that is reasonable in the circumstances. That gives a well-prepared contractor real leverage: a transparent, well-evidenced position framed as the fair value is far more persuasive than an aggressive number, and far more likely to survive to certification. Fairness cuts both ways, but it favours the party who has done the analytical work.

The most profitable variations are the ones valued before they become contentious. Agreeing the basis - contract rate, new rate, or daywork - and the resource build-up up front removes the ambiguity that later becomes a dispute. That is the whole thrust of getting your commercial house in order early, which we cover in preventing disputes over variation valuation before they start, and it is exactly the kind of upstream discipline our prevention service is built around.

Frequently Asked Questions

When can I use a new rate instead of the contract bill rate for a variation?

A new rate becomes appropriate when the varied work is no longer similar in character to a billed item, when it is carried out under materially different conditions, or when the change in quantity is large enough that the original rate no longer recovers your costs. The bill rate is the default only while the assumptions behind it still hold. Test every instructed change against character, conditions, and quantity - if any of the three has shifted materially, you are entitled to build up a new rate rather than accept the original one by habit.

How is a new rate for a variation actually calculated under FIDIC?

It is usually built up rather than negotiated as a lump sum. Start from any relevant contract rate as a base and adjust it for the element that differs - harder access, extra labour, smaller batch size, additional plant time. Where no comparable rate exists, build the rate from the reasonable cost of labour, plant, and materials, plus overhead and profit allowances consistent with the rest of the contract pricing. The key is documenting the build-up transparently so the Engineer can see it mirrors the contract's own logic and has little basis to discount it.

What is daywork and when should I use it?

Daywork values work by recording the actual resources used - labour hours, plant, and materials - at agreed daywork rates plus contractual additions, rather than by measuring a quantity and applying a rate. It suits minor, incidental, or highly variable work that cannot sensibly be measured, where the scope is open-ended. Use it when defining and rating a quantity would be artificial. The critical condition is record-keeping: daywork sheets must be captured contemporaneously and signed by the Engineer's representative, because unsigned, reconstructed daywork is routinely rejected at valuation.

Can I claim extension of time as well as cost for a variation?

Often yes, but the two are separate entitlements and both must be pursued. If the varied work extends activities on the critical path, you may be entitled to an extension of time and the time-related prolongation cost that comes with it, in addition to the direct cost of the added work. The mistake is settling the money and staying silent on the programme. Flag the time impact when the variation is instructed and valued, and keep the records that link the change to the delay, so the larger prolongation element is not lost by default.

Why do SME contractors so often lose money on variations?

Three recurring reasons. They price only the bare cost of the added work and ignore ripple effects like disruption and time-related preliminaries. They accept contract rates for work that has moved into materially worse conditions where a new rate was justified. And they fail to record daywork properly, so it cannot be substantiated. A fourth is submitting round-number lump sums that invite negotiation downward instead of transparent build-ups that hold their value. Each is avoidable with disciplined valuation and contemporaneous records applied at the moment of instruction.

Value every variation on the basis the contract actually allows, and record it as you go - that is where the margin is won or lost.

Note: This article is general information on FIDIC variation valuation and is not legal advice; the correct basis depends on your specific contract, bill of quantities, and particular conditions.