How to handle variations on a construction project

What actually counts as a variation

A variation is any change to the scope you originally priced and agreed - work added, work taken out, or work altered from what the drawings, specification or quote described. It doesn't have to be dramatic. Swapping a specified tile, moving a partition wall by 400mm, adding an extra socket outlet, hitting unexpected ground conditions, or the client deciding halfway through first fix that they want two more radiators - all of these are variations.

The trap most contractors fall into is treating small changes as favours rather than variations. There's no size threshold. If it wasn't in the original scope, it's a variation, and it needs to be dealt with as one - however minor it looks on site at the time.

The golden rule: capture it in writing, price it before you start

Everything else in this guide is detail. This is the rule that actually protects your margin: get the change in writing, price it, and get it agreed before you do the work - not after.

Once the work is done, your negotiating position collapses. The client knows you can't undo it, so there's no pressure on them to agree a fair price - or any price at all. "We'll sort it out at the end" almost never means what you hope it means. Do the paperwork first, every time, no matter how small the change or how well you know the client.

How to price a variation properly

Rushed variation pricing is where most of the money leaks away. Treat it with the same discipline as the original quote, not a back-of-a-van guess. Work through:

• Labour - hours realistically needed, at your actual charge-out rate, plus supervision time if the change needs managing.
• Materials - priced at today's cost with your normal markup applied, not the margin-free "mate's rates" that creep in under pressure on site.
• Plant and equipment - extra hire, fuel, consumables, and any additional access equipment the change pulls in.
• The knock-on effect on time and prelims - the one everyone forgets. If the variation adds three days to the programme, your prelims (supervision, welfare, security, plant standing time) run for three extra days too, and every trade behind you may need reprogramming. Omissions can shrink the programme just as much as additions extend it - factor that in both directions.

If the change disrupts sequencing, price the disruption itself, not just the extra materials. Loss of productivity from working out of sequence is real cost, and it's recoverable if you've noted it at the time.

Get written instruction or sign-off before you proceed

A price without an instruction to proceed is just a quote sitting in someone's inbox. You need both: the change priced, and a clear "yes, go ahead" from someone with authority to give it - the client, the main contractor's site manager, or the architect/contract administrator, depending on the setup.

Authority matters. An instruction from a site foreman with no budget sign-off isn't worth much if the client later disputes it. Know who can actually authorise spend, and get your sign-off from them.

Email is fine. A signed variation order is better. A scribbled note on a drawing, photographed and sent back with "confirming as discussed, price attached, please confirm to proceed" works too. What matters is that it exists, it's dated, and it shows a price was communicated and accepted before the work started.

The contract mechanism: instructions, confirmation of verbal, day-works

If you're working under a formal contract (JCT or similar), there's usually a proper mechanism for this - don't bypass it because site life moves faster than paperwork.

• Architect's/Employer's Instructions (AI/EI) - the formal, contractually recognised route for a design team to instruct a change. Keep every one - they're your strongest evidence at final account.
• Confirmation of Verbal Instruction (CVI) - most contracts let you confirm, in writing, a verbal instruction given on site, and this stands unless disputed within a set number of days. Use this constantly.
• Day-works rates - for work too disruptive or ill-defined to price in advance (breaking out unknown ground conditions, say), agree day-works rates for labour, plant and materials up front. Then record actual hours and materials daily and get them signed off on site, not weeks later from memory.

Whichever route applies, learn the mechanism in your contract and use it every time, not just when the change feels big enough to bother with.

Keep a variations register

Every job of any size should have a single, running log of every variation raised. For each one, record: date raised, description, who instructed it, the price, whether it's agreed, whether it's invoiced, and its status.

This stops variations getting forgotten between the moment they happen and the final account - exactly when memory fails and paperwork goes missing - and gives you a running total of the job's real value versus the original contract sum. Review it weekly, not just at the end: a five-minute check on a Friday catches gaps while they're still easy to fix. This is the sort of thing dedicated job management software for project-based trades is built to make routine rather than a spreadsheet chore.

Dealing with verbal "just do it" instructions on site

This is where most unpaid variations are born. A client or site manager says "yeah, just move the socket over there while you're at it" - said casually, agreed casually, then never mentioned again until the final account argument.

The fix isn't to refuse verbal instructions; site doesn't work like that, and refusing every small ask makes you a nightmare to work with. The fix is to always follow up, the same day: "Per your instruction on site today, I'll do X. This is a variation to the agreed scope - I'll get a price to you by [date]." That single message converts a verbal instruction into a written one and starts the clock on getting it agreed.

Never let more than one variation build up unrecorded. Chasing paperwork for a £40 extra feels disproportionate - but three months and forty small "just do its" later, that's easily £3,000–4,000 of genuinely extra work with no record it was ever agreed.

How unbilled variations quietly erode your margin

Nobody loses money on variations in one dramatic hit. It happens a pound at a time - an extra hour here, a bag of materials there, a day's delay absorbed because raising it felt awkward. None of it shows up as a loss on any single day. It shows up as a job that should have made 15% margin actually making 6%, with nobody able to say quite where the difference went.

The explanation is almost always the same: work genuinely outside the original scope, done in good faith, never priced, never agreed, never invoiced. It's not usually that clients are deliberately exploiting you - it's that unrecorded extras are invisible by default, and invisible costs don't get paid. Treating every scope change as a variation to be logged and priced, even the ones that feel too small to bother with, is the single biggest lever most trades businesses have to protect margin they're already earning but not collecting.

Getting variations onto the next application for payment

A priced, agreed variation is worth nothing until it's on an invoice or application for payment. Don't let agreed variations sit in a folder waiting for the final account - include them in your next interim application as a matter of routine, listed as separate line items against their variation reference, not buried inside the main works valuation.

Listing them separately makes it obvious to the client or quantity surveyor exactly what they're paying for, which speeds up approval, and gives you a clean paper trail if any one variation is queried or valued down - you can defend that line without the whole application being held up. If a variation is agreed but not yet complete, apply for the value done to date, same as the main contract works.

Whatever system you use to track jobs - see our pricing if you're weighing up dedicated software against a spreadsheet - the discipline matters more than the tool: raise it, price it, get it agreed, invoice it, and don't let it wait.