A builder can only charge for genuinely unforeseen work agreed with you before it happened, or work clearly outside the original written scope. If it was foreseeable, already covered by the quote, or never discussed, you are entitled to query it and ask for evidence before paying anything.
Variations, provisional sums and genuine extras — the difference
Three different things get lumped together as 'extras' and they are not the same. A variation is a change you asked for — moving a socket, upgrading a tap — priced and agreed before the work happens. A provisional sum is an allowance in the original quote for something not yet specified, such as tiling at £30/m² with the final area to be measured. A genuine extra is unforeseen work discovered once something is opened up, such as rotten joists behind a wall that could not have been seen at quotation stage.
Only the first and third should ever appear as additional charges, and both should be documented before the work is carried out, not after the invoice arrives.
What a builder is and is not entitled to charge for
- Entitled: unforeseen conditions that could not reasonably have been identified during a survey or quote visit (drainage in poor condition, damp behind plaster, inadequate foundations).
- Entitled: changes you requested after work started, once priced and agreed.
- Entitled: provisional sum items once the actual quantity or specification is confirmed, matched against the rate stated in the quote.
- Not usually entitled: work that a competent survey should have identified before quoting.
- Not usually entitled: the builder's own errors, rework, or having under-priced the original job.
- Not usually entitled: anything never mentioned to you until the final invoice.
The written variation process that prevents this dispute entirely
The single biggest cause of disputed extras is a verbal conversation on site that one party remembers differently from the other. A simple written variation process avoids this: when something changes, the builder (or you) writes down what is different, the price impact, and any effect on the programme, and both parties sign or confirm by text or email before work continues.
This does not need to be formal. A dated WhatsApp message saying 'as discussed, opening up the bay window has found rotten timber, replacing will cost an extra £450, please confirm to proceed' followed by your written 'agreed' is enough to remove the argument later.
How to respond to an invoice for work you never approved
- Do not pay on the spot simply to avoid an awkward conversation — a paid invoice is much harder to query afterwards.
- Ask, in writing, for a clear breakdown: what the extra work was, why it was necessary, when it was carried out, and why you were not told beforehand.
- Compare it against your original quote and any specification to check it is not something already covered.
- If it relates to opening-up work, ask for photographs taken at the time — a competent builder will usually have these anyway.
- Set out, calmly and factually, that you were not consulted before the work went ahead and ask for this to be reflected in the final figure.
Evidence to gather before you respond
- The original quote and specification, in full.
- Any written or messaged conversations about the job, in date order.
- Photographs of the property before work started, if you have them.
- Photographs the builder has taken of the issue that supposedly required extra work.
- A note of dates: when the issue was found, when you were told, when the work was done.
When a genuine extra is reasonable to pay
Not every disputed extra is unreasonable. Older properties in particular often reveal problems only once plaster, floors or render come off — rotten timber, undersized drainage, or asbestos-containing materials are common examples that no visual survey would have caught. Where the evidence supports this, and the price is proportionate to the work and materials involved, paying a fair extra is normal and reasonable.
The issue is rarely whether extras exist at all on a real project — they often do — but whether you were told before the cost was committed, and whether the amount is justified.
If you cannot agree
If a builder insists on charging for something you consider was already covered or should have been foreseen, try to resolve it directly and in writing first. If that fails, Citizens Advice can explain your general consumer rights, and trade body membership (such as FMB or NFB) may offer a dispute resolution service if the builder belongs to one.
Practical checklist
- Get the original quote and specification in writing before work starts
- Ask for any assumptions or exclusions to be stated explicitly
- Agree that no extra work proceeds without a written variation first
- Request photographs whenever opening-up work reveals a problem
- Keep every site conversation confirmed in a text or email afterwards
- Query any invoice before paying it, not after
- Compare invoiced extras line by line against the original scope
- Ask why you were not consulted before extra work went ahead
- Check provisional sum items against the rate stated in the quote
- Note dates for when issues were found versus when you were told
- Ask whether the builder's insurance or trade body has a dispute process
- Never pay in full simply to end an uncomfortable conversation
Good and bad examples
What good looks like
The builder messages before opening a wall: 'Found damp timber lintel, needs replacing, £280 extra, photos attached, let me know to proceed.' You reply 'agreed' and the cost is on record before the work happens.
What to push back on
An invoice arrives at the end of the job with a single new line: 'Additional works £1,850' with no breakdown, no prior conversation, and no supporting photographs.
Worked example
Illustrative variation record for a kitchen extension
| Date | Item | Reason | Agreed price | Confirmed by |
|---|---|---|---|---|
| 12 Feb | Extra socket, utility room | Homeowner request | £65 | Text message |
| 18 Feb | Replace rotten joist | Found on opening up floor | £310 | Email, photos attached |
| 25 Feb | Upgrade tiling to porcelain | Provisional sum, final choice | £420 (was £280 allowance) | Signed spec change |
Commonly missed items
- No written record of the conversation before extra work started
- No photographs of the problem that supposedly justified the cost
- No comparison against the original quote before paying
- Assuming a verbal mention on site counts as approval
- Not checking whether the item was already a provisional sum in the quote
Warning signs
- Extras only ever appear on the final invoice, never during the job
- No photographs or evidence offered when asked
- Vague descriptions such as 'additional works' with no breakdown
- Pressure to pay immediately before you can check anything
- A pattern of underquoting followed by large 'unforeseen' additions
Questions to ask
- Can you show me photographs of what you found?
- Why wasn't I told about this before the work was carried out?
- Is this already covered by a provisional sum in the quote?
- Can you break this cost down into labour and materials?
- What would this have cost if agreed in advance?
When to seek professional advice
- The builder refuses to provide any evidence or breakdown for a disputed extra
- The sums involved are large relative to the whole project
- The relationship has broken down and written correspondence is not resolving it
- You are being asked to pay before you can properly check the claim
Official sources
Frequently asked questions
- Can a builder legally charge for extras without my agreement?
- Consumer protection generally expects services to be carried out with reasonable care and skill and at a reasonable price if none was agreed. Citizens Advice can explain how this applies in general terms — get specific advice if you are unsure.
- What if the extra work was already discussed verbally on site?
- A verbal conversation may still count as agreement, but it is far harder to prove later. Always follow up any site conversation with a text or email confirming what was said.
- Should I withhold payment if I disagree with an extra?
- You can query an invoice and ask for it to be broken down before paying. Whether you can lawfully withhold payment depends on your contract — Citizens Advice can point you to general guidance.
- Is it reasonable for older properties to reveal extra costs?
- Yes, this is common with older buildings once walls or floors are opened up. The key question is whether you were told before the cost was committed and whether the price is proportionate.
- What should a written variation include?
- What has changed, why, the price impact, any effect on timescale, and confirmation from both parties before the work proceeds.
Builder Proof UK publishes general educational information for homeowners. It is not legal, structural, surveying, planning, electrical, gas, insurance or financial advice, and it does not replace advice from a suitably qualified professional for your specific project.