A variation is a change to the works from what the contract described: more work, less work, different work, or a change to the conditions and constraints under which the work is done, such as access, sequence or working hours. Standard forms define the term widely, but none of them pays for change that was never instructed and never recorded.
Under JCT contracts, variations are instructed by the contract administrator, and the valuation rules follow a hierarchy: contract rates where the varied work is of similar character and conditions, adjusted rates where it is similar but not identical, fair valuation where nothing else applies, and daywork where the work cannot properly be measured. Instructions are meant to be in writing; in practice much begins as a conversation, which is why confirming verbal instructions promptly is old but living advice.
NEC contracts run change through the compensation event machinery instead: an instruction changing the Scope is a compensation event, priced through a quotation built on Defined Cost plus the Fee and assessed prospectively wherever possible. The system is admired for keeping change current, and it is unforgiving of parties who let notification and quotation deadlines slip.
Most variation disputes trace back to process breaking down under pace. Work is changed on a nod at the workface, the instruction is confirmed late or never, the changed work is done and covered up, and by the final account nobody can agree what was original scope, what was design development and what was genuinely varied. The argument about whether something is a variation at all is often harder than the argument about its value.
The commercial rule is simple: a variation is worth what you can evidence. That means the instruction, or the request and conduct that imply one; the changed work itself, photographed before, during and after; the resources it consumed, day by day; and its effect on time, noted while the sequence was still visible. Records made in the moment settle in weeks what reconstructions argue about for years.
Construction Metric captures that daily evidence automatically from the site WhatsApp group; its JCT page shows how the record lines up with JCT’s valuation machinery.