Scenario: the owner’s site engineer instructs the EPC contractor to reroute a pipeline and add an equipment plinth — “do it now, paperwork later”. The contractor completes it and, four months later, submits a variation claim of nearly 2 billion dong; the owner refuses: no variation order approved by the authorised person. This is the variation-dispute script repeated on almost every EPC project: the work is buried in the ground, and nobody wants to pay for it. This article analyses the variation-order principle, “constructive change” through oral instructions, and how each side protects itself.
The core principle: no authorised VO, no automatic right to payment
A standard EPC contract places a strict gate over every change: work outside the contract scope becomes payable only with a written variation order/instruction signed by the contractually authorised person, with pricing mechanics from contract rates or pre-agreement before execution. The gate exists for budget and authority reasons: site personnel usually hold technical authority (directing the works) but not financial authority (committing the owner’s money). Veteran contractors know: a technical instruction and a variation order are two different documents; following a technical instruction while skipping the variation order means voluntarily carrying the payment risk.
For the owner, the VO gate also protects against “drip-feed variations”: dozens of unapproved “small” changes can aggregate to 15–20% of the contract price and skew both programme and overall design with nobody accountable for the whole.
Constructive change and the exceptions that save contractors
Sites do not run like textbooks: the owner/supervisor sometimes orally directs work entirely different from approved drawings, rejects shop drawings forcing a costlier method, or demands standards above the contract. Law and arbitral practice recognise the exception group commonly called constructive change: if the contractor proves (1) the instruction came from the owner side/its de facto authorised person, (2) the work executed lies outside the original scope rather than being another reading of the same duty, and (3) the contractor timely notified that it treated the matter as a variation, reserving money/time rights — the payment claim can stand despite the missing standard VO.
Condition (3) is where most contractors lose: “notifying” four months after completion reads as waiver or as ambushing the owner’s budget control. The site golden rule: every oral instruction departing from drawings is confirmed in writing within 24–48 hours with a reservation line — “we treat this as a variation under clause… and will price/notify time impact” — one such email completely changes the evidence balance.
Pricing and time for VOs: use the mechanism, avoid fighting over every dong
VO pricing follows the contract’s ordered mechanism: existing contract rates for similar items; if none, rates derived from the nearest items; only then negotiated new rates on cost analysis. In parallel, every VO has two faces — money and time: a contractor claiming money but forgetting to notify programme impact within the contractual window loses the extension for that very change (linking to EOT/LDs disputes). The owner needs a living variation register: each change numbered, with approval status, estimated value and cumulative percentage against the contract price — when the cumulative figure hits a warning threshold (the base design changed too deeply), that is the signal to stop and review the whole instead of signing the next small VO. Most EPC budget disasters come not from one large VO but from 60 “small” ones nobody totalled.
Frequently asked questions
What is a variation order in EPC?
A document signed by the contractually authorised person directing work outside/changed from the original contract scope, with pricing mechanics and time adjustment. Without an authorised VO, a contractor executing variations on a mere technical instruction has no automatic right to payment — the VO gate is the EPC contract’s core budget control.
Can a contractor be paid for orally instructed work departing from drawings?
Possibly, under the constructive-change exceptions: proving the instruction came from the owner side/its de facto authorised person, the work lay outside the original scope, and — decisively — the contractor timely notified that it treated the matter as a variation, reserving money/time rights. Reporting months after completion collapses the claim.
By what mechanism is a variation order priced?
In the contract’s order: existing rates for similar items; rates derived from the nearest items; then negotiated new rates on cost analysis. Programme impact must also be notified in time to preserve the extension right — a VO always has a money face and a time face.
How is the “work first, paper later” dispute avoided?
The 24–48-hour rule: every oral instruction departing from drawings is confirmed in writing with a variation reservation; the owner maintains a cumulative VO register by percentage of contract price, and both sides’ site staff have technical authority (directing works) clearly separated from financial authority (signing VOs).
This article has been quality-reviewed by the FLAW AI Legal Council