Variations: how a job grows after you agreed the price

Short answer

A variation is a change to the scope you agreed. It should be documented before the work is done, describing what changed, why, what it costs and what it does to the timeline, and you should agree to it in writing. Verbal variations agreed on site are the single most common cause of a final invoice that bears no relation to the quote.

Nearly every job of any size has at least one. Something is found in a wall, you change your mind about a fitting, a supplier discontinues a product. Variations are normal. Undocumented variations are not.

What a variation should contain

  • What is changing, described as specifically as the original scope was.
  • Why — a client request, a site condition discovered, a supply problem.
  • The cost effect, up or down. Variations can reduce a price and should be recorded when they do.
  • The effect on the timeline, which is often larger than the cost effect and more often forgotten.
  • Your agreement, in writing, before the work happens.

The rot: verbal variations

The pattern is familiar. Something comes up, it is discussed on site, the answer is "we'll sort it out at the end", and at the end there is a number nobody can now reconstruct. By then the work is done and undoing it is not realistic, which is precisely why the conversation should happen before.

When you can refuse

You can decline a variation. What you cannot usually do is decline it and still require the original completion — if a genuine site condition means the agreed scope is no longer buildable, that has to be resolved rather than ignored. Where you have real leverage is on variations that are not genuine: work that should have been foreseen and priced, or that was always going to be needed and was left out to make the quote look competitive.

How to keep them under control

  1. Put a variation clause in the original agreement: nothing extra proceeds without written approval.
  2. Ask for a running total, not just per-variation figures. Six small variations are easy to agree to individually and startling in aggregate.
  3. Get the timeline effect stated each time. This is the one that quietly turns a three-week job into a three-month one.
  4. Keep every message in one thread, so the sequence is reconstructable later.

If a dispute follows, the documentation is what decides it. A tribunal comparing your dated written approvals against a recollection is not weighing two equal accounts.

Common questions

Do I have to pay for a variation I did not agree to?
Generally not, if you genuinely did not authorise it — the agreed contract price covers the agreed scope. In practice it turns on evidence, which is why written approval matters so much. Where a variation was unavoidable and you benefited from it, a tribunal may still allow a reasonable amount, so refusing to engage is not a strategy.
Can a variation reduce the price?
Yes, and they should be recorded when they do. If something is removed from the scope — you supply the fittings, or a section is deferred — that is a variation downward and belongs in writing exactly like an increase.
What if the tradesperson refuses to document variations?
Treat it as a serious warning about how the rest of the job will go. Document it yourself instead: send an email after each conversation setting out what you understood was agreed and what it costs. An unanswered email confirming your understanding is significantly better evidence than nothing.

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