Materials Gone Up? How to Protect Yourself from Price Increases

Written by Tom Ellis · Senior Trades Editor

Last updated: 9 November 2026

Quick Answer

Once you've given a fixed-price quote, you're generally bound by it unless your contract includes a materials price variation clause. For jobs taking longer than 2–4 weeks, always include a provisional sum for materials or a price-fluctuation clause. For work already under way, most customers will accept a variation notice with evidence of the price increase — be transparent, show the invoices.

Fixed price vs estimate — the key difference

This distinction matters legally. A fixed-price quote(also called a lump-sum contract) means you've agreed to do the work for a set amount. Unless your contract specifically carves out material price fluctuations, you bear the risk of cost increases.

An estimateis different — it signals that the final price may vary. Courts have consistently held that an estimate is not a binding fixed price, though it shouldn't vary significantly without telling the customer. The word matters: use “estimate” when you genuinely can't fix the price, and “quote” only when you can.

Many tradespeople blur this line accidentally — they say “the job will cost £4,500” verbally, then it comes in at £5,200 due to materials. Without a written variation clause, that extra £700 is at risk.

What happens if you just absorb the increase

If you don't have a variation clause and you've given a fixed quote, you have two choices: absorb the loss or have a conversation with the customer. The law doesn't automatically entitle you to pass on cost increases — that's the risk you took when you quoted a fixed price.

The commercial reality is that absorbing significant increases — say, timber up 20% on a large carpentry job — can wipe out your margin entirely. The earlier you spot and communicate a material change, the more receptive customers tend to be.

How to protect yourself before quoting: provisional sums

A provisional sumis an allowance built into your quote for work or materials that can't be precisely priced at the time of quoting. The quote shows the provisional figure, with a note that it will be adjusted to actual cost when the materials are purchased.

Example language for a quote:

Labour and installation: £2,400

Materials (provisional sum based on current prices): £1,800

Note: Materials will be invoiced at actual purchase price. The provisional sum above is based on prices as at [date] and may vary if prices change before purchase.

This is entirely legitimate and professional — large construction contracts use provisional sums routinely. For domestic jobs, explain it to the customer briefly: “I've given you a fixed price for my labour and a materials estimate — if prices move significantly before I buy, I'll let you know before ordering.”

How to write a materials variation clause

For longer jobs or repeat commercial clients, include a variation clause in your standard terms and conditions. Here's a plain-English version:

Materials price variation clause

“All prices quoted for materials are based on current supplier prices at the date of this quotation. If the cost of materials increases by more than 5% between the date of quotation and the date of purchase, we reserve the right to adjust the materials element of the contract price accordingly. We will notify you in writing before purchasing materials if such an adjustment is required.”

The 5% threshold is a sensible buffer — small fluctuations are part of the business, but significant spikes shouldn't come out of your pocket.

Telling a customer mid-job: what to say

If you're already on a job and materials prices have jumped, the conversation works best when you:

  1. Show the evidence— bring the supplier invoice or screenshot showing the price change. “I quoted timber at £X per sheet in October — it's now £Y” is much harder to argue with than a vague claim.
  2. Quantify the impact— “The increase affects about £400 of this job” is easier to process than “prices have gone up a lot.”
  3. Issue a formal variation notice— put it in writing, even just an email. “This is to advise that materials costs have increased by £X. Please confirm you're happy for me to proceed on this basis.”
  4. Give them a choice — if you can substitute a cheaper material without affecting quality, offer that option too.

When a customer refuses to pay the difference

If you don't have a variation clause and the customer says no, you're in a difficult position legally. You can:

The lesson is preventative: build it into your quotes before the job starts, not after.

Using historic prices when quoting for future work

For projects with a long lead time between quoting and starting, consider:

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