You ask three builders to price the same loft conversion and get back £38,000, £51,000 and £67,000. Nobody is necessarily ripping you off. Far more often the three quotes describe three different jobs, and the gap is made of things nobody wrote down. Learning how to compare builder quotes in the UK comes down to one habit: give every builder the same written brief before any of them opens a notebook.
The short answer: a quote is only comparable if all three builders priced the same scope, the same materials and the same exclusions, so write that down once and send it to all of them. The cheapest figure on the table is rarely the cheapest job, and the dearest is rarely the best one.
Why three quotes rarely match
Quotes differ for a handful of dull reasons, none of which show up in the headline number.
Different scope. One builder includes making good and decorating, another stops at plaster.
Different materials. “Kitchen units” can mean a £3,000 supply or a £12,000 one.
Provisional sums. A line such as “Tiling: £1,500 provisional” is a guess that becomes your problem when the real cost is higher.
Different assumptions about problems. One quote allows for the rotten joist you may find, another assumes you will not.
VAT. Some quotes include it, some add it at the end, and a builder who is not VAT registered will not charge it at all.
Our guide to how to read a builder’s quote goes line by line through what each of these looks like on paper.
Step 1: write one brief and send it to everyone
Most people describe the job out loud on site visits and each builder hears something slightly different. Instead, write a one-to-two page brief and email the same document to all three.
What the brief should contain
The outcome in plain words, for example “replace the family bathroom, 2.1m by 1.8m, with a walk-in shower, wall-hung toilet and heated towel rail”.
Who supplies what. State whether you are buying the tiles, the sanitaryware and the fittings, or whether the builder is.
Finish level. Name the standard you expect: skim and paint, tiled floor to ceiling, new flooring.
Access and constraints. Parking, working hours, pets, a neighbour on a party wall, a listed building.
Your target start and end dates, and whether those are firm.
If drawings exist, send them. If the job needs building control or planning approval, say who is responsible for applying and paying.
Step 2: ask for the same format back
Ask each builder to return an itemised quote, not a single figure. At minimum you want labour, materials, any subcontractors, a contingency line, VAT treatment and a start date and duration. A builder who refuses to itemise is telling you something useful.
Ask three further questions in writing, so the answers sit next to the quote:
What is not included?
Which items are provisional sums, and how will any difference be handled?
What is the payment schedule, and what triggers each payment?
On that last point, the structure matters as much as the price. Our guide to stage payments explains why a large deposit up front is a warning sign and how to tie payments to finished work.
Step 3: build a simple comparison grid
Put the three quotes in a spreadsheet with a row for each item in your brief and a column per builder. Where a builder has left a row blank, do not assume it is included. Write “not stated” and go back and ask.
Then add up the totals twice: once as quoted, and once with every provisional sum and exclusion replaced by a realistic number. The second total is the one to compare.
A worked example
Take a bathroom refit. Builder A quotes £6,800 including tiling and fittings. Builder B quotes £5,200 but lists the sanitaryware as a £900 provisional sum and excludes tiling. Builder C quotes £7,400 and includes a £500 contingency for hidden pipework. Once you add a realistic £1,600 for tiling and £1,400 for sanitaryware to Builder B, it becomes £8,200, the most expensive of the three. The cheapest quote was the least complete one.
Three traps that make quotes look comparable when they are not
The “lowest price” anchor. Once one number is on the table, the others get judged against it. Resist the urge to tell builders what the competition quoted, which only encourages cuts you will not see until the job is under way.
The verbal add-on. Anything agreed on site that is not written down (“we’ll sort the skirting boards”) has a habit of turning into an extra. Ask for every change to be confirmed by email, with the cost, before it happens.
The rushed decision. A builder who says the price is only good until Friday is selling, not quoting. A sound quote stays valid for a reasonable period, usually 30 days, and a good builder will accept that you want time to compare. Build in a week to ask follow-up questions, because the second round of answers is often where the real differences appear.
Beyond price: what else to check
My view: I would pay up to 10% more for the builder who gave me the clearest written quote and the most specific answers, because vagueness on paper becomes an argument on site. A tidy, detailed quote shows a builder who has thought about your job rather than reached for a number.
Before you choose, check each builder for:
Public liability insurance, with a certificate you can read.
Registration with a body such as TrustMark where relevant to the work, and Gas Safe or NICEIC for gas and electrical elements.
References you can phone, ideally from a job of similar size in the past year.
Guarantees, in writing, with the start date and the length of cover.
A realistic start date. A builder who can start next week for a big job is either very quiet or not planning properly.
For wider context on typical prices by job type, our building work costs hub is a useful sense check on whether any figure is wildly out of range.
What to do in the next 30 minutes
Write a one-page brief for your job: outcome, who supplies what, finish level, dates.
List the questions you want every builder to answer in writing.
Create a blank spreadsheet with your job items down the side and three columns for the builders.
Email the same brief to three registered or recommended builders today.
Ask each of them to confirm what is excluded and which items are provisional.
Ready to keep the brief, the three quotes and your comparison grid in one place? Compare quotes in Home+ and store each builder’s paperwork against the job, so the winning quote is easy to find if there is ever a disagreement.
FAQ
How many quotes should I get for building work? Three is the usual number and a sensible one: enough to spot an outlier without drowning you in site visits. For large or complex projects such as an extension, getting more detailed quotes from two or three well-vetted builders beats collecting six rough ones.
Is the cheapest builder quote always the best? No. The cheapest quote is often the least complete, with provisional sums, exclusions or thin materials allowances. Compare totals after you have replaced every guess with a realistic figure.
What is a provisional sum in a builder’s quote? It is an allowance for a cost that is not yet known, such as tiles you have not chosen. If the real cost is higher you pay the difference, so ask the builder to explain how any difference will be calculated and agreed.
Should a quote include VAT? A VAT-registered builder normally has to charge VAT on building work, with reduced or zero rates applying in some cases. Ask every builder to show VAT clearly so the totals compare.
Can I negotiate a builder’s quote? Yes, but negotiate scope rather than just price. Dropping an item, supplying materials yourself or being flexible on start date can reduce the figure without lowering the quality of the work.
Is a quote legally binding? A written quote that you accept can form the basis of a contract, but an estimate is only a rough guide. Ask for a fixed-price quote in writing and agree how variations will be priced before work starts.
