SiteKiln gives you plain-English information, not legal advice. It's aimed at small UK construction businesses. Laws change and every job is different, so speak to a solicitor or adviser before you rely on this for a real dispute.
Clients adding "just a few extra bits" is normal -- doing them for free every time is how you work evenings for nothing.
1. The short version
Legally, there's no automatic right to extra money just because you did more work; you need either a contract clause that lets you charge for variations, or a clear agreement (even by text) that extra work costs extra, and if there's nothing in writing you're into messy quantum meruit territory -- arguing later over a "reasonable sum" for what you did.
2. Where you stand legally
- A variation is any change to the original agreed scope -- additions, omissions, substitutions, or changes in quality/spec.
- There is no automatic right to be paid more just because the work changed; you usually need to show:
- The extra work was not already included in the original price.
- The client (or someone properly authorised) asked for or clearly accepted the change.
- There was an express or implied promise to pay extra.
- Any contract requirements (like giving written variation notices) were followed.
- If you do extra or higher-spec work without instruction, you're usually stuck with the original price.
- Where there's no agreed price for extra work but it's clearly outside scope and requested, courts can fall back on quantum meruit -- paying a reasonable amount for the extra work to avoid unjust enrichment.
- Consumer-law regulators (CMA etc.) are hot on pricing transparency and "add-on" charges:
- Mandatory charges and extras must be clear up front, not sneaked in later.
- Hidden or surprise extras can be treated as unfair commercial practices.
So, legally you want: a variation clause in your terms, plus a habit of agreeing extras and prices in writing before you lift a tool.
3. Work out if it's scope creep or already included
Before you argue for extra money, make sure you're not charging twice.
Compare with your original documents:
- Quote / spec / drawings -- does this item appear there already?
- Any assumptions listed (e.g. "up to 10 sockets", "painting walls only").
Typical "creep vs included" examples:
- Extra lights, sockets, radiators beyond what's shown -- usually extras if your quote was specific.
- Additional rooms or areas not in the original spec -- extras.
- Reasonable making-good or small snags to get you up to a normal trade standard -- usually included, not extra.
Check how it came up:
- Did they say "while you're here, can you also..." with no mention of price?
- Did you say "we'll sort that" without saying it costs more?
Sense-check:
- If another builder read your quote, would they think this work was in or out of scope?
If it's genuinely extra, you're entitled to charge -- the trick is capturing that before you do it.
4. Set the rules up front (in your quotes and T&Cs)
The best way to kill scope creep is before it starts.
In your quote/contract, include
- A clear description of what's included -- rooms, fixtures, quantities.
- A short variation clause, e.g.:
"Any additional work or changes requested by the client which are outside the scope of this quote will be treated as a variation and charged at £X/hour plus materials, or at an agreed fixed price, and must be confirmed in writing before the work is carried out."
Make it clear
- That changes may affect price and timescale, and you'll confirm this before going ahead.
- That you're not obliged to carry out extras if you can't agree a price or it clashes with other work.
Be upfront about call-out or small-works minimums
E.g. "Additional minor works requested during the project are subject to a minimum charge of £X."
This isn't about being awkward; it's about making it normal that extra work = extra money and putting that expectation in writing.
5. Handle "while you're here" requests on site
This is where most scopes actually creep.
When they ask
- Don't say "yeah, no problem" and crack on.
- Say "Yes, we can do that -- it's extra and will cost about £X and add Y time. Do you want me to price it properly?"
Then
- Text or email a simple line: "Extra: supply and fit 3 x downlights in hallway -- £X including materials and labour. This is in addition to the original quote."
- Ask them to confirm in writing ("Yes, go ahead") before you start.
For small stuff
- You can work off a pre-agreed day rate / hourly rate plus materials, but still confirm roughly how long you expect it to take.
If they won't confirm
- It's okay to say "I can't do that extra today without agreeing the price -- let's sort it properly in writing and I can come back."
Every extra you capture like this is one less argument about "I thought it was included" at the end.
6. If you've already done extras with nothing agreed
Sometimes you only realise it's scope creep when you're doing the final bill.
Work out:
- Exactly what extra you've done beyond the quote.
- Rough time and materials for each item.
Then decide how hard to push:
- For clear, chunky extras they obviously asked for (extra room, extra radiator), you can reasonably bill them and explain why.
- For small bits you never priced and never mentioned, sometimes it's smarter to write them off and call it a lesson.
If you do bill:
- Keep it modest and fair, not a surprise gouge.
- Be ready to explain: "Original quote covered X. You then asked us to add Y and Z. I should have priced it there and then -- that's my mistake -- but I do need to charge something for that extra work. I've kept it to £[reasonable figure]."
If they flat-out refuse:
- You may have a quantum meruit argument for a reasonable sum for the extra work, but it's a fight and you'll need good records.
The aim is to avoid this mess by fixing the habit on future jobs, not to spend your life arguing over three extra sockets.
7. Common mistakes
- Doing extras without agreeing price first -- it feels "helpful" in the moment; later it's your word against theirs and often ends up as free work.
- Writing vague scopes that invite arguments -- "full refurb" with no detail is an open door to "I thought that was included".
- Letting the client rewrite the job on the fly -- changing layout, spec and sequence without resetting price and programme is how you lose weeks and money.
- Trying to charge full whack after the fact -- big, surprise extras on the final invoice (with nothing agreed on price at the time) look bad and are hard to enforce; courts expect clear variation agreements.
- Hiding mandatory charges -- sneaky "extras" that were really always part of the job can be treated as unfair or misleading pricing, especially under the CMA's price transparency focus.
8. Who to contact
- Citizens Advice / Business Companion -- guidance on fair pricing and extras, exactly what your customers will see: businesscompanion.info (free)
- Trade bodies / contract consultants -- many have template variation forms and model contracts with solid variation clauses (varies)
- Solicitor or construction contract adviser -- for drafting robust T&Cs and variation processes on bigger jobs, and for serious disputes about large unpaid extras (paid)
9. Sources and legislation
- Consumer Rights Act 2015 -- Part 1, Chapter 4 (services: reasonable care and skill, reasonable price). legislation.gov.uk/ukpga/2015/15
- Consumer Protection from Unfair Trading Regulations 2008 -- misleading pricing, charges, unfair add-ons. legislation.gov.uk/uksi/2008/1277
- CMA guidance on pricing practices -- transparency requirements for mandatory fees and extras. gov.uk/government/publications/pricing-practices-guide
- Quantum meruit -- common law principle: reasonable payment for work done outside the agreed scope where no price was set.
- Variations in construction contracts -- contractual requirements for instructing and valuing changes.
10. Related guides on this site
- 9.1 Customer won't pay the final invoice
- 9.3 Customer changed their mind mid-job
- 9.11 Customer demanding a refund -- when you have to and when you don't
- 8.5 Writing quotes that protect you
- 8.6 Terms and conditions template -- domestic work
- 8.14 Dealing with price increases on materials mid-job
- 2.5 Variation orders -- protecting yourself
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