The homeowner's side of a variation
On a build I project managed, the builder put in a timber ridge beam where the structural drawings said steel. Building Control found it. I did not, and it had been sitting up there about six months by then.
It was sorted inside a week and it never turned into a payment dispute. But afterwards, I read every invoice differently, and he never really regained my trust after that. I do not think he was being dishonest. He almost certainly thought he was saving everyone a fuss.
It is rarely about the amount
That is the bit worth understanding from where the client sits. The argument is rarely about the amount. Two thousand pounds agreed beforehand is a purchase. The same two thousand on an invoice three weeks later feels like something was taken.
Some of that is just how homeowners hold the money. Most are paying out of savings, and by the time you are on site every pound has a job already. There is no contingency line in a normal person's head. So when you say it will be another two grand, what they hear is that the island is gone, or the flooring drops a grade, or the holiday does. Tell them instead that it is another two grand and the obvious places to find it are the worktop or the landscaping, and you are in a completely different conversation, because now they are choosing rather than losing.
Most of your clients cannot judge you
The rest of it is that most of your clients have no way to judge you. Close to half are doing their first renovation. They cannot tell an honest unforeseen cost from being taken advantage of, so with nothing to go on they assume the worst.
That is not about you.
The client you surprise still pays you, usually. They just do not recommend you.
Show them the hole
It also makes the fix cheaper than it looks. Show them the hole. Walk them out to the drain that was not on any drawing. Five minutes of that and it stops being a bill and turns into a decision they were part of, and they will repeat your explanation to their friends for two years afterwards, near enough word for word.
Write it down before you do it
So write the change down before you do it, price it, and get it signed. Keep it off the stage payments too, so nobody loses track of what was original scope. It takes minutes. Our survey puts referrals and word of mouth at 65% of new work, which is really the whole argument: the client you surprise still pays you, usually. They just do not recommend you.
| Agreed before the work | Raised after the work | |
|---|---|---|
| Written record | Scope, price and days added, signed by both | An invoice line the client has not seen before |
| The client's position | Choosing whether to spend | Being told what they owe |
| Effect on the programme | Known and agreed up front | Argued about while the job is live |
| If it is disputed | You have the signed variation | It is your word against theirs |
| Typical outcome | Paid with the next stage | Paid late, or not in full |
Frequently asked questions
Does a variation have to be agreed in writing?
Not by law. The Construction Act's payment and adjudication rules do not apply to work carried out for a residential occupier, so there is no statutory requirement covering variations on a domestic job. What binds you is your contract. The standard forms are built around written instructions rather than site conversations: under a JCT contract, a change to the scope is dealt with as a written instruction, which is precisely what stops a variation turning up as a surprise on a later invoice. If you are working to a bespoke contract, write the clause in yourself. Without one, a disagreement comes down to two people remembering a conversation on site differently, which is not a position either side wants to be in.
Can a builder charge for extra work without telling me first?
They should not, and a good one will not. Genuinely unforeseen work does come up once floors and walls are opened, but the point at which it is discovered is the point to raise it, not the next invoice. If a charge appears for work you never approved, ask for it in writing with the reason and the price, and treat the answer as a signal about how the rest of the job will go.
What should a written variation actually include?
Five things: a plain description of the change, the cost, the days it adds to the programme, whether it moves any stage payment trigger, and both signatures with a date. It takes minutes and it is the document everyone reaches for if the final invoice is ever questioned.
Should a variation be folded into a stage payment?
No. Keep variations on a separate running list with its own total. Stage payments are usually tied to verifiable milestones, so quietly adding extras to one breaks the link between the payment and the work it was meant to certify. At the end of the job, that separate list is what explains the gap between the contract sum and the final invoice.
What if we have already fallen out over a variation?
Most of these settle without anyone going near a court. 65% of the contractors we surveyed resolve payment disputes by direct negotiation, and 24% have gone as far as legal action or small claims. Put your position in writing, set out what was agreed and when, and propose a specific resolution. Mediation or an ombudsman scheme is the next step, with court genuinely last.
Related guides
Ian Packard runs BuildWiz, a step-by-step guide for UK homeowners project-managing their own builds. For the homeowner's full playbook on deposits, stage payments and variations, read his guide: Builder Deposits and Stage Payments in the UK.
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