A practical guide for UK subcontractors, not legal advice. Your subcontract decides how variations must be instructed, valued and notified, so check its wording.
What counts as a variation
A variation is any change to the work in your subcontract: extra work, less work (an omission), a change to the specification, the sequence, the working hours or the access you were promised. Under most subcontracts, including the JCT forms, a variation has to be instructed by the main contractor before you are entitled to be paid for it.
Instructions arrive in many forms: an architect's instruction (AI) passed down the chain, a contractor's variation instruction (CVI), a variation order (VO), a site instruction, an email, or a word from the site manager. The form matters less than having a record that someone with authority asked for the change.
The most expensive habit: working on a verbal instruction
A site manager asks for six more sockets on level 2. Your electrician fits them that afternoon. Three months later, at the final account, nobody remembers asking, and there is nothing in writing. That is how variations are lost.
When the instruction is verbal, confirm it in writing the same day. A short email is enough: "Confirming your instruction today to fit six additional double sockets to level 2 kitchens. We will price this and include it in our next application." Keep the reply, or the lack of one.
Keep a variation register
Log every change the day it arrives, even before you have priced it. A register needs, as a minimum:
| Ref | Date | Instruction | Description | Status | Our value | Their valuation |
|---|---|---|---|---|---|---|
| V001 | 5 Oct | AI 14 | Additional sockets to level 2 kitchens | Agreed | £2,450 | £2,450 |
| V002 | 12 Oct | Site instruction | Relocate distribution board DB3 | Instructed | £1,890 | £1,500 |
| V003 | 20 Oct | Email from QS | Upgrade emergency lighting to self-test | Quoted | £3,200 |
Track each one through its status: notified, quoted, instructed, agreed, disputed, omitted or rejected. The gap between your value and the main contractor's valuation is your final account in waiting, so record theirs as soon as you know it.
You can download our free variation register template (Excel) to start one today.
Pricing a variation
Your subcontract usually sets out how variations are valued. A common order of preference is:
- The rates in your contract, where the varied work is similar to work already priced.
- Rates adjusted from your contract rates, where the work is similar but the conditions or quantities differ.
- A fair valuation, where there are no comparable rates.
- Dayworks, where the work cannot be measured, recorded on signed daywork sheets at agreed rates. Our guide to daywork sheets explains how.
Show your build-up: labour hours, materials, plant and any time-related costs such as extra supervision. A quotation with a clear build-up is far easier to agree than a single figure.
Do not forget the knock-on effects. A change that delays your other work, or forces you to return to an area you had finished, has a cost beyond the change itself. Many subcontracts require you to notify delay or disruption within a set time, so check the notice provisions as well as the payment ones.
Claiming variations in your payment applications
- Include instructed and agreed variations in every application, valued to date, in their own section below the contract works. Our payment application checklist shows where they sit.
- Include disputed variations too, at your value, so the main contractor has to deal with them in their payment notice. Leaving them out can look like agreement.
- Keep notified and quoted changes on your register until they are instructed, and chase the instruction.
- Carry them forward cumulatively, like the rest of the application, so nothing drops off between months.
If the main contractor values a variation lower, or leaves it out, their payment notice should say so and give the basis. Check it against the deadlines in our guide to payment notices and pay less notices.
Common mistakes
- Starting the work before the instruction is confirmed in writing.
- Pricing late, so the conversation happens at the final account when memories have faded.
- Editing the contract sum analysis instead of adding a variation, which loses the record of what changed. See our guide to contract sum analysis.
- Missing contractual notice periods for delay and disruption.
- Not recording the main contractor's valuation, so the size of the gap is a surprise at the end.
Constructicore's variations register logs every instruction with its value and status, records the main contractor's valuation beside yours, and claims instructed and agreed variations straight into your next application.
Published 26 October 2026.