Pricing and quoting, 28 October 2026
Variations in construction: what to do when the customer wants extra work mid-job
"While you're here, could you just..." You say yes, you do the work, and at the end the customer says they thought it was included.
Variations in construction are changes to the work you agreed to do. The fix is simple.
Price the extra, get the customer to agree it in writing, then do it. Add it to your next invoice as its own line.
In short
- A variation is any change to the agreed work: extra work, less work or different work.
- Stop and price it before you start. Use the same rates as your original quote where you can.
- Get a yes in writing. A text or email that names the work and the price is far better than a nod on the drive.
- Put each variation on the invoice as its own line, with a reference number.
- With no agreed price, a homeowner only has to pay a reasonable price, so agree the price first.
What is a variation in construction?
A variation is a change to the work in the original contract or quote, asked for or agreed after the price was set. In the trade it's often just called "extras".
It can go three ways:
- Added work. For example, 4 more sockets on a kitchen rewire.
- Less work. The customer decides to keep the old fireplace, so you don't take it out.
- Different work. Porcelain tiles instead of ceramic, or a different boiler model.
A variation order is the written instruction or form that records the change. On bigger jobs the main contractor's quantity surveyor (the QS, the person who measures and values the work) issues it. On a small domestic job, you usually write it yourself.
Why do variations cause so many arguments?
Variations cause arguments because they're agreed in a hurry and rarely written down. The customer remembers a smaller price, or thinks it was part of the job all along.
Three things usually go wrong:
- The extra is agreed out loud, with no price.
- The work gets done before anyone talks money.
- The invoice shows one big total, so the customer can't see what the extras were.
The time to agree the price is before you pick the tools up. Once the work's done, you've lost most of your leverage.
What does the law say if you never agreed a price?
If a homeowner asks for extra work and no price is agreed, consumer law says they must pay a reasonable price, and no more. That's in section 51 of the Consumer Rights Act 2015.
What counts as "reasonable" is a question of fact. In plain terms, you may end up arguing about it, maybe in front of a judge. That's why a written price beats relying on the law.
Be careful what you say, too. Section 50 of the same Act matters here.
What you tell a customer about the work can become part of the contract if they rely on it. Say "that'll only be a couple of hundred" and you may be held to it.
Does the Construction Act cover variations?
The Construction Act covers payment on most commercial jobs, not on most homeowner jobs. Its full name is the Housing Grants, Construction and Regeneration Act 1996.
Its payment rules don't apply to a contract with a residential occupier. That means work mainly on a house or flat the customer lives in, or plans to live in.
On jobs it does cover, two rules help you get paid for variations:
- Stage payments. If the work will take 45 days or more, you're entitled to be paid in instalments. So variations can go on each valuation (the regular sum of how much work is done so far).
- Payment notices. Each payment needs a notice saying the sum due and how it was worked out. Our guide to payment and pay less notices explains how they work.
The Act covers England, Wales and Scotland. Northern Ireland has its own version, the Construction Contracts (Northern Ireland) Order 1997.
On a main contract, check the contract's variation clause too. Some say a change only counts if it's instructed in writing. Ignore that and you may not get paid for the extra.
How do you price a variation?
Price a variation the same way you priced the job, using the rates in your original quote where the work is similar. If the work is different, price it fresh.
Work through it in this order:
- Labour. Hours times your day or hourly rate.
- Materials. At today's merchant price, not last month's.
- Knock-on costs. Extra skip, extra scaffold hire, another trip to the merchant, making good.
- Time. Will it push the finish date back? Say so.
- Overheads and profit. Add your usual margin. Extras aren't favours.
If you can't price it up front, agree to do it on dayworks. Dayworks means you're paid for the hours, materials and plant you actually use, at agreed rates. Keep a daily sheet and get it signed.
Our guide on how to price a job covers the costs small contractors forget. You can check your margin with the free markup and margin calculator.
A worked example
A sparky is rewiring a kitchen for a fixed £3,200. Halfway through, the customer asks for 4 more double sockets and an outside light.
| Item | Cost |
|---|---|
| Labour: half a day at £240 a day | £120 |
| Materials: sockets, back boxes, cable, outside light | £95 |
| Making good the plaster round the new boxes | £40 |
| Subtotal | £255 |
| Markup at 15 per cent on cost | £38.25 |
| Variation price | £293.25 |
This is a worked example, not real job figures. The point is the order. Every cost goes on, then the markup, then the customer agrees the total before the first box is cut in.
How do you get a variation agreed in writing?
Send the customer the change and the price in writing, and ask them to reply "agreed" before you start. A text, WhatsApp or email is fine on a small job, as long as it's clear.
Keep it to one variation per message. Give each one a number, so the invoice can match it later.
A variation form you can copy
Variation number: V[number]
Job: [customer name and address]
Date asked for: [date] Asked for by: [name]What's changing: [describe the extra, reduced or different work in plain words]
Price: £[amount] (plus VAT if you charge it)
Effect on finish date: [none, or the new date]Customer's agreement: Please reply "agreed" to this message, or sign below. I'll start this work once you've agreed.
Signed: [customer] Date: [date]
Take a photo before and after the extra work. Keep it with the variation. If anyone asks later, you can show what changed.
How do you make sure variations get paid?
You make sure variations get paid by invoicing them as separate lines, each with its variation number and agreed price. The customer can then match every extra to a message they agreed to.
Before you send the final invoice, run through this checklist.
| Check | Done? |
|---|---|
| Every variation has a number and a written yes | |
| Each one is a separate line on the invoice | |
| Omissions (work taken out) are credited too | |
| Dayworks sheets are signed and attached | |
| Before and after photos are saved with the job | |
| On a main contract, variations are on the valuation |
Taking omissions off honestly matters. It shows the customer the extras are fair, and they're more likely to pay without a row.
If they still don't pay, follow the steps in how to chase an unpaid invoice.
Where Nexley fits
Nexley is the AI back office for UK trade firms. Five AI assistants do your office work overnight, from quotes and invoices to tenders and supplier orders, and you approve each one from WhatsApp.
Variations in construction are where a lot of small firms leave money on the table. With Nexley, you can talk the extra through in a voice note and get it priced on your own rate card. It's sent to the customer and agreed in writing before the work is done.
That gives you the paper trail you need when it's time to invoice. See how Nexley's quoting software for builders handles quotes and variations, or look at Nexley's pricing.
Common questions
What is a variation order in construction?
A variation order is the written instruction that changes the work in a construction contract. It says what's changing and, ideally, the agreed price and any change to the finish date.
On a main contract, the QS or contract administrator usually issues it. On a domestic job, your own written variation, agreed by the customer, does the same job.
Do I have to do extra work the customer asks for?
It depends on your contract. Read what it says about changes before you agree or refuse.
On a main contract, the variation clause often lets the client instruct changes, and says how they're valued. On a small homeowner job with a simple quote, talk it through and agree the extra like a new mini job.
Can I charge for extra work I didn't quote for?
Yes, you can charge for extra work the customer asked for, even without a quote. But with no agreed price, a homeowner only has to pay a reasonable price.
That's harder to prove than a price they agreed in writing. If you did extra work the customer didn't ask for, getting paid is much harder. Always ask first.
What's the difference between a variation and dayworks?
A variation is the change to the work. Dayworks is one way of paying for it.
You can price a variation as a fixed sum before you start. Or you can do it on dayworks and charge for the time and materials used. A fixed price is usually less hassle. Dayworks suits work you can't measure up front.
Sources
This page is general guidance, not legal advice. For a large or disputed sum, get your contract checked.
- Consumer Rights Act 2015, section 51: reasonable price for a service (legislation.gov.uk) (legislation.gov.uk)
- Consumer Rights Act 2015, section 50: what the trader says becomes binding (legislation.gov.uk) (legislation.gov.uk)
- Housing Grants, Construction and Regeneration Act 1996, section 106: contracts with a residential occupier (legislation.gov.uk) (legislation.gov.uk)
- Housing Grants, Construction and Regeneration Act 1996, section 109: stage payments (legislation.gov.uk) (legislation.gov.uk)
- Housing Grants, Construction and Regeneration Act 1996, section 110A: payment notices (legislation.gov.uk) (legislation.gov.uk)
- Construction Contracts (Northern Ireland) Order 1997 (legislation.gov.uk) (legislation.gov.uk)
Topic: Pricing and quoting
Keep reading
Pricing and quoting
How to quote faster as a tradesperson: from voice note to sent quote
Most quoting time goes on looking up prices and retyping the same lines. Here's a five-step flow from voice note to sent quote, a rate card checklist, and a worked example of what slow quoting costs a heating firm.
Pricing and quoting
How to work out your overheads per man-day
Every day on site has to pay for the van, the insurance and the days you don't work. Here's how to put a number on it, with a worked example from a six-person roofing firm and a calculator for your own.
Pricing and quoting
Markup vs margin in construction: the difference and what it costs you
Markup and margin use the same profit but divide it by different numbers. Here's the conversion table, a worked example of what mixing them up costs on a £20,000 job, and calculators for both.
