Compare Guide · Updated June 2026 · UK Extensions

Compare Builders: How to Vet Extension Quotes in 2026

The cheapest quote is rarely the best one. To compare builders properly you need to price the same scope with each, read the quotes line by line, and check credentials, references and the contract before any money changes hands. Get at least 3 quotes and you will quickly see the market rate and spot the outliers. This 2026 guide shows exactly how to vet a quote, what a good one includes, and the red flags that should make you pause.

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Updated June 2026
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The Checklist · 2026

What a Good Builder Quote Includes

A proper quote is itemised, not a single bottom-line number. Use this checklist to judge whether each quote gives you enough to compare fairly and to hold the builder to.

Quote should showWhy it matters
Itemised labour and materialsLets you compare like for like
Stage payment scheduleProtects you from large upfront deposits
Exclusions and provisional sumsShows what is not in the price
VAT positionAvoids a 20 percent surprise
Start and finish datesSets a realistic programme

If a quote is a single figure with no breakdown, ask for it in writing and itemised before you compare it with the others.

Green Lights and Red Flags

What to Trust and What to Question

✓ Good signs

  • An itemised written quote
  • Public liability insurance and references
  • A stage payment schedule, modest deposit
  • Membership of a trade body such as the FMB
  • Happy to show completed work

✗ Red flags

  • A large upfront deposit demand
  • Cash only with no paperwork
  • A price far below the others
  • No written contract offered
  • Pressure to start immediately
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How to Compare Quotes Fairly

The most common mistake is comparing quotes on the bottom-line total. The cheapest figure is often the one that has left items out, so a like-for-like comparison only works when every builder has priced the same written scope and drawings. Hand each of them the identical brief, then read the quotes side by side, item by item.

Look closely at exclusions and provisional sums. A quote that looks GBP 5,000 cheaper may simply have excluded the foundations or the finishes that the others included. Once the scope matches, the right choice is the builder who scoped the job most thoroughly and prices it fairly, not the lowest number on the page.

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FAQ · 2026

Comparing Builder Quotes FAQs · 2026

Get at least 3 quotes for any extension. Three lets you spot an outlier that is suspiciously cheap or expensive and gives you a true sense of the market rate. Make sure each builder is pricing the same scope so the comparison is fair.
A proper quote is itemised and shows labour, materials, a stage payment schedule, what is excluded, the VAT position, a start and finish date, and an allowance for known unknowns such as foundations. A one-line total with no breakdown is a red flag.
Give every builder the same written scope and drawings so they price like for like, then compare line by line rather than on the bottom-line total. Check what each one has included or excluded, because the cheapest headline figure often leaves out items the others priced in.
Watch for a large upfront deposit, cash-only pricing, no written contract, no insurance or trade references, a price far below the others, and pressure to start immediately. Any one of these is a reason to pause and check before you commit.
No. The cheapest quote is often the one that has left things out, underestimated the job, or plans to claw the difference back through variations later. Choose the builder who scoped the work most thoroughly, has solid references and prices fairly, not simply the lowest number.
Ask for public liability insurance, references from recent similar jobs, and ideally membership of a trade body such as the FMB. Look at reviews, ask to see completed work, and make sure there is a written contract before any money changes hands.
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