Projects rarely blow their budgets on the contract sum — they blow them on the changes. Some variations are unavoidable (you can’t see inside a wall), some are self-inflicted (you changed your mind about the kitchen), but all of them are manageable with one habit that takes thirty seconds per change.

The one rule

Nothing changes until the change has a written price and time effect, agreed before the work is done. An email or WhatsApp is fine:

“Confirming today’s discussion: move the utility door to the side wall. £340 + VAT, no programme change. Please go ahead.”

That’s a variation order. Ten of those over a project is a tidy audit trail; ten verbal “yeah just do it”s is a £6,000 argument in the final week. Write the rule into the contract and — more importantly — actually follow it when the job is friendly and everyone trusts everyone. That’s precisely when the undocumented extras accumulate.

Where changes come from

  • Client changes — you upgrade, move or add something. Entirely legitimate extras; your job is to decide with the price in front of you, not after.
  • Unforeseen work — opened-up problems: rot, bad wiring, missing lintels. Legitimate if genuinely unforeseeable; the builder should stop, show you, and price the fix before proceeding.
  • Design gaps — the drawings were silent, someone assumed. Whose cost this is depends on what the quote reasonably included; a “fixed price for the works shown” pushes design-gap risk toward whoever produced the design.
  • Provisional sums firming up — the quote’s allowances (kitchen £4,000, tiles £30/m²) becoming real numbers. Not really variations at all: track each against its allowance so the running total never surprises you.

Pricing a variation fairly

Anchor prices to what the contract already tells you:

  1. Contract rates first — if painting a room was £X in the quote breakdown, painting a similar room is a similar figure.
  2. Day rates + materials where no rate fits — sanity-check labour against UK trade day rates and materials against the Cost Index.
  3. Omissions credit back. Variations cut both ways: dropped work is money returned at the same rates it was priced in, not quietly absorbed.

Ask for the running variation total with every stage payment — a one-line “contract £80,000; variations to date +£3,240” keeps the final account boring, which is the goal.

Extras appearing at the end

The final invoice arrives with £4,800 of items you never agreed. Your position is stronger than most homeowners assume:

  • Work you never asked for, on a fixed-price scope, is the builder’s cost — a fixed price means the builder took the risk of their own pricing.
  • Work you did ask for but never priced isn’t a blank cheque: as a consumer you owe a reasonable price for it (Consumer Rights Act 2015), which you can benchmark and challenge line by line.
  • Pay the undisputed part promptly, dispute the rest in writing with your counter-figures, and if it escalates, follow the dispute route. Courts are unsympathetic to contractors who did extra work without ever mentioning a price — and equally unsympathetic to clients who clearly ordered work and hoped it was free.

Keeping change from killing the programme

Every variation nudges time as well as money — and accumulated small changes are how a 12-week job becomes 16. Agree the time effect in the same message as the price (“+2 days” or “no change”), and watch the completion date move only through those written agreements. It keeps delay accountability clean in both directions.

This guide is general information for homeowners in England and Wales, not legal advice.