How to compare builders quotes properly is mostly about making them comparable before you look at the totals. Three quotes for the same extension can differ by thousands simply because one includes scaffolding, skips and building control and another leaves them out. This page shows how to get quotes that can be lined up, the lines that must appear on each, and the checks we would make on any Kent builder before signing.
Start with one brief for every builder
The single biggest cause of quotes that cannot be compared is that each builder priced a slightly different job. The Federation of Master Builders recommends giving every builder exactly the same information, ideally detailed drawings with measurements, so that the prices can be compared like for like. Its guide to getting a quote for building work also recommends three quotes, warning that going beyond three or four becomes counterproductive and that some builders will not tender against a long list.
Your brief should include:
- The drawings and, for structural work, the engineer’s calculations.
- Whether planning permission or a lawful development certificate is in place, and any conditions attached.
- A written specification: what finishes, what level of fitting out, who supplies the kitchen, sanitaryware or flooring.
- Your intended start date and any fixed deadlines.
- Known site issues: restricted access, a shared drive, trees, drains, a party wall.
Allow time. The FMB notes that a thorough quote can take a few weeks to produce, and a builder who sends a three-line price by text a day after visiting has not costed your job in any detail.
Quote or estimate: know which you have
An estimate is a builder’s informed guess and can change. A quote is a fixed price for the work described, as long as the specification does not change. Ask for a written quote, not an estimate, and check the document actually says “quotation”.
If you go ahead with no price agreed at all, the Consumer Rights Act 2015 says you must pay a reasonable price for the service and no more. That sounds protective, but what counts as reasonable is a question of fact, which in practice means an argument after the work is done. A written fixed price avoids it.
The nine lines every quote should show
Put the quotes side by side and check each one for the following. Where a line is missing, ask the builder in writing whether it is included, excluded or priced elsewhere.
- Preliminaries. Scaffolding, skips, site welfare, protection to the existing house, and the final clean. These are the easiest items to leave out of a low price.
- Groundworks and foundations. Excavation, spoil removal and the foundation design assumed. Ask what happens if the building control inspector asks for deeper foundations.
- The main build, broken into stages: shell, roof, windows and doors, first fix, plastering, second fix.
- Provisional sums. Allowances for items not yet designed or chosen. Check each one is realistic; a low provisional sum is a future extra.
- Prime cost (PC) sums. Allowances for items you will choose, such as the kitchen or tiles. Check whether the builder adds a handling or fixing charge on top.
- Fees. Building control fees, structural engineer, party wall surveyor if needed. Some quotes include them, many do not. Our page on Building Regulations approval explains how the Kent fees work.
- Making good. Repairing the existing house where the new work joins it: plaster, decoration, flooring, the garden.
- VAT. Check every total is shown on the same basis, with or without VAT.
- Exclusions. A clear list of what is not included is a good sign, not a bad one. It shows the builder has thought about the job.
Normalise the totals before you compare
Once you have the nine lines, build a simple table with one row per line and one column per builder. Where a builder has excluded something another has included, enter your own estimate for it, or ask for a price. Only then add up the columns. The cheapest headline figure often stops being the cheapest once its gaps are filled.
Two points on VAT. A builder only has to register for VAT once taxable turnover passes £90,000 over 12 months, according to HMRC’s rules on GOV.UK, so a smaller firm may legitimately not charge it. That is a real saving, not a warning sign in itself. But a VAT-registered builder offering a discount for cash with no invoice is a warning sign, because you lose your paper trail and any comeback.
Be wary of a quote far below the others. The FMB’s advice is plain: if something seems too good to be true, it usually is. A very low price usually means the builder has misread the scope, has left things out, or plans to recover the difference through extras.
Read the payment terms as closely as the price
How and when you pay matters as much as how much. Look for:
- A small deposit, if any. Trading standards advice is that deposits are usually only justified where materials have to be made to order or the job is long. Never pay most of the cost up front.
- Stage payments tied to finished stages, such as foundations passed by building control, roof on, plastering complete, rather than to dates.
- A retention. Many contracts hold back a small percentage until snagging is finished. Ask whether the builder will accept one.
- How extras are priced and approved. Insist on written agreement of the price before any extra work starts.
Check the builder, not just the quote
A good quote from a firm you cannot trace is worth little. Before you sign:
- Ask for proof of public liability insurance and check the dates.
- Look up the company on Companies House if it is a limited company, and check the trading address.
- Check membership claims directly with the body named, such as the FMB or TrustMark, rather than relying on a logo.
- In Kent, search the county council’s Trading Standards Checked directory. Members have been vetted, including credit checks and an insurance check, and the scheme is free to search.
- Ask to see or speak to the owner of a similar job finished in the last year or two.
Our page on house extension builders in Kent goes through the questions to ask at the first site visit, and the Contemporary Structures homepage links to cost guides for extensions, roofs, kitchens and bathrooms you can use to sanity check any total.
Frequently asked questions
How many builders quotes should I get?
Three is the usual recommendation, including from the Federation of Master Builders. Beyond three or four the process tends to waste everyone’s time, and some good builders will decline to price against a long list.
Is a builder’s quote legally binding?
A written quote that you accept forms part of the contract, so the builder should stick to it for the work described. An estimate is not fixed. Changes you ask for are extras and can be charged, which is why every change should be priced in writing first.
Why are builders quotes so different?
Usually because they priced different jobs: one included scaffolding, skips, fees or making good and another left them out, or the provisional sums differ. Normalise the quotes line by line before comparing totals.
Should I always pick the cheapest quote?
No. Compare like for like first, then weigh the price against the builder’s track record, payment terms and how clearly the quote is written. A detailed, slightly higher quote is usually cheaper by the end of the job than a vague low one.
Should I pay a builder a deposit?
Only a small one, and only where there is a reason, such as made-to-order windows or a long project. Pay in stages as work is completed and never pay for work that has not been done.
Do builders charge for quotes?
Most do not for small jobs, but some charge for a fully costed quote on a large project because it takes days to prepare. If a builder charges, ask whether the fee is deducted from the contract price if you go ahead.
