Variations
Contract rates or a new price for extra work?
The answer is in your own bill: if the extra work looks like something you already priced, that price governs, whether it now suits you or not. The skill is knowing when it stops looking similar, and saying so before the work is done rather than after.
QScope Team·18 February 2026·5 min read
Fifty extra metres of the same blockwork you priced in the bill: contract rate, no discussion. A skylight in a roof you never priced at all: new price. Most extra work sits between those two, and the argument is about which side of the line it falls.
The rule, and why it cuts both ways
Your contract sets the valuation rules, and the standard forms share the shape: work of similar character, done under similar conditions, is valued at the contract rates. That binds both directions. A rate you priced keen in the bill stays keen in the variation, and a rate you priced fat stays fat. Nobody reopens rates because the job turned out harder than hoped.
Where the character is similar but the conditions or quantities are not, the contract rate is the starting point and gets a documented adjustment: same blockwork but at height, in winter, in ones and twos instead of a run. Show the adjustment, not just the answer.
Where nothing in the bill resembles the work, you are at a fair valuation, and your records carry the whole figure. See the full valuation ladder, and dayworks for work that cannot sensibly be measured at all.
The stronger move: a price before the work
Many contracts allow a quotation for a variation: you price it, they accept, then you build it. Where the mechanism exists, use it for anything big, because it converts a future argument into a present decision, with time and cost dealt with together.
Three traps, all from real jobs:
- Quoting without a deadline for acceptance. Prices age. Say how long it stands.
- Starting before acceptance. The moment you start, you have surrendered the leverage the quotation existed to give you.
- Quoting cost and forgetting time. If the change needs programme, the quotation is the moment to say so, not the final account.
On a domestic job, the same, only more so
None of this depends on the Construction Act, so it works unchanged for the family whose house you are extending. A fixed price agreed in writing before the change is built is the single best dispute-prevention tool on a domestic job, because it replaces an argument about fairness with a document both of you signed.
What to do this week
1. Before pricing any extra, open your own bill first and ask which rung you are on. Write the rung on the build-up.
2. For anything above a day or two of work, quote before you build, with a validity date and the time effect stated.
3. Keep the instruction and the price together on one record, because a price without an instruction is half a variation. See confirming what was said on site.