To compare builder quotes fairly, line up each one against the same scope of work and specification rather than the total price alone, check what each includes and excludes, note any provisional sums, and query anything missing before deciding. The lowest total is often lowest because it excludes items another quote has included, not because the work is genuinely cheaper.
Why three quotes rarely price the same job
Ask three builders to quote the same extension and you'll usually get three different scopes back, not just three different numbers. One assumes you're supplying the kitchen. One has included scaffolding and one hasn't. One has priced a higher specification of window because that's what they usually fit. None of this is necessarily dishonest — it's just that without a very tight specification document, everyone fills the gaps with their own assumptions.
Comparing quotes properly means putting them on the same footing before you compare the totals, otherwise you're not choosing the best builder — you're choosing whoever left the most out.
Build a like-for-like comparison table
The most useful thing you can do is create a simple spreadsheet or table with one row per stage or trade (groundworks, structure, roof, first fix, plastering, second fix, external works, decoration) and one column per quote. Fill in what each builder has priced for each row, including 'not stated' where a quote is silent on something.
This exercise on its own usually reveals the differences that the total price hides — one builder may have included the electrics rewire and another assumed only new circuits for the extension, for example.
Check specification, not just scope
- Are window and door specifications equivalent — same glazing performance, same materials?
- Is the roof covering the same type and quality across quotes?
- Are kitchen and bathroom allowances (provisional sums) similar, or is one quote using an unrealistically low placeholder?
- Do all quotes include the same decoration standard — one coat versus two, for example?
- Are electrical and plumbing fittings comparable in number and quality?
Normalise the exclusions
List every exclusion stated in each quote — scaffolding, skips, building control fees, party wall costs, engineer's fees — then add back an estimate for anything a particular quote has left out but the others include, so you can see what each job would genuinely cost you overall.
This step is where most of the apparent price gap between quotes usually closes. A quote that looks £8,000 cheaper can turn out roughly level once scaffolding, skips and fees are added on.
Look past the total to the payment schedule and timeline
Two quotes at a similar price can still carry very different risk. Compare deposit size, how payments are staged, and whether a retention is held back until snagging is cleared. A slightly higher quote with a fairer payment schedule and a shorter, more realistic timescale can be the better decision even before workmanship is considered.
Weigh price against evidence of reliability
Once quotes are genuinely comparable on scope and price, the deciding factor is usually confidence in the builder rather than the last few hundred pounds of difference. That's a separate exercise from comparing the paperwork — see our guide on checking a builder for the checks worth doing before you commit.
Practical checklist
- List every quote's scope stage by stage in one table
- Mark where a quote is silent on a stage or item
- Compare specification of windows, doors, roof covering and fittings
- Compare provisional sum allowances for kitchens, bathrooms and sanitaryware
- List every exclusion stated in each quote
- Add back a realistic figure for anything excluded from one quote but included in others
- Compare deposit size as a proportion of total price
- Compare how many payment stages there are and what triggers each
- Check whether any quote holds a retention until snagging is complete
- Compare stated start dates and durations
- Check insurance is confirmed for each builder, not just the cheapest
- Ask each builder to clarify anything unclear before making a decision
- Don't automatically discount the highest quote without checking what it includes
Good and bad examples
What good looks like
A homeowner obtaining three loft conversion quotes builds a simple table covering staircase, structural steel, insulation, windows, electrics, and decoration. It reveals that the cheapest quote excludes the staircase entirely, assuming the existing one will be reused — once priced in, the three quotes come within a few hundred pounds of each other, at which point the decision is made on the builder's manner and references rather than price.
What to push back on
Choosing the lowest of three total figures without checking scope, then discovering midway through the job that scaffolding, an extra structural beam and the electrics rewire were never included and are billed as additional cost.
Worked example
Illustrative comparison only — figures are for illustration, not typical prices
| Item | Quote A | Quote B | Quote C |
|---|---|---|---|
| Base build price | £42,000 | £38,500 | £45,000 |
| Scaffolding | Included | Excluded (est. £1,800) | Included |
| Kitchen allowance | £6,000 | £3,500 | £6,000 |
| Decoration | Included, 2 coats | Excluded | Included, 2 coats |
| Adjusted total (approx.) | £48,000 | £47,300 | £51,000 |
Commonly missed items
- Failing to check specification is equivalent before comparing price
- Not adding back excluded items before judging which quote is cheapest
- Ignoring differences in payment schedule and deposit size
- Comparing only the headline total rather than a stage-by-stage breakdown
- Not asking each builder the same clarifying questions
Warning signs
- A quote that is dramatically cheaper with no obvious reduction in scope or specification
- A builder who won't clarify what's included when asked directly
- Quotes that are impossible to compare because none of them break the price down
- Pressure to decide quickly before you've had time to build a proper comparison
Questions to ask
- Can you confirm exactly what's included in the total price?
- How does your specification for windows and roofing compare with what I've asked other builders to quote?
- What's your provisional sum allowance for the kitchen and bathroom based on?
- Is scaffolding, skip hire or waste disposal included or separate?
- What would you say sets your price apart from a quote a few thousand pounds lower?
When to seek professional advice
- If the quotes are for a large or structurally complex project, consider a quantity surveyor or architect to check like-for-like pricing
- If you can't get quotes to align even after asking clarifying questions, that itself may be a reason to be cautious about a particular builder
- If you're unsure about specification terms (U-values, damp-proofing methods, and so on), ask Planning Portal or Building Control guidance (planningportal.co.uk) or an independent professional
Official sources
Frequently asked questions
- Is it rude to ask a builder to clarify their quote against a rival's?
- No — a professional builder expects to be asked to clarify what's included, and most will do so without issue. If a builder reacts badly to reasonable clarifying questions, that reaction is itself useful information.
- Should I tell builders what others have quoted?
- You don't need to share figures, but it's reasonable to ask each builder to confirm scope items such as scaffolding, decoration or specific specification, so you can compare consistently without disclosing competitors' prices.
- How much difference between quotes is normal?
- There's no fixed rule, but a wide spread often points to differing scope or specification rather than one builder being simply better value. Investigate the gap before assuming either the cheapest or the most expensive is wrong.
- Should I always avoid the cheapest quote?
- Not automatically — a lower quote can be genuine if the builder has lower overheads or a leaner supply chain. The point of comparing like for like is to find out whether it's genuinely cheaper for the same work, rather than cheaper because something has been left out.
- What if two quotes look identical once compared?
- Then the decision reasonably comes down to other factors — the builder's manner, references, insurance, and how clearly they've communicated so far. See our guide on checking a builder for that side of the decision.
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.