How to Check Out a Builder Before You Sign: A Due Diligence Checklist

There is an odd asymmetry at the start of every building project. Your builder will check your ability to pay — a deposit up front, stage payments, sometimes a credit check. Most homeowners, meanwhile, hand over a six-figure commitment to a company they met three weeks ago, on the strength of a friendly conversation, a tidy quotation and a folder of photographs that may or may not be of their own work.

Almost every renovation horror story I have been called in to rescue traces back to something that would have been visible before anyone signed. Not hidden, not subtle — visible, in a free public register, to anyone who spent an hour looking.

This is that hour. It costs under £50 in total and it is the highest-return time you will spend on the whole project.

Not at this stage yet? If you are still buying — weighing up a property you have viewed, or trying to work out how alarming a survey really is — that is a different question, and I cover it through Chat to Your Builder, an independent builder review service for buyers. Same principle as this article: builders who never quote for the work, so there is nothing riding on the answer.

Part 1: Is the company real, and is it solvent?

Start with the name. Take the exact company name and registration number from the quotation — not the trading name on the van, the legal entity on the paperwork — and look it up on Companies House (find-and-update.company-information.service.gov.uk). It is free and it takes ten minutes.

What you are looking for:

• Does the name on the quote match a real registered company? A quote from "Smith Builders" where the contract is with "SB Construction (London) Ltd" is a distinction that matters enormously if things go wrong. You need to know precisely which legal entity you are contracting with.
• Incorporation date. A company incorporated four months ago, run by someone claiming twenty years in the trade, is not automatically a problem — people do leave and set up on their own. But it is a question to ask, and the answer should be straightforward.
• Filing history. Overdue accounts are a warning. A "first Gazette notice for compulsory strike-off" is a serious one — it means the company is on its way to being struck off the register for not filing. Do not sign anything with a company in that state.
• Accounts. Small companies file very little, but you can usually see net assets. A company with negative net assets is being funded by somebody, and on a building job that somebody is often the next client's deposit.
• The directors, and what else they have run. This is the important one. Click through to each director and look at their appointment history. A trail of dissolved companies, each lasting two or three years, at the same registered address, doing the same thing, is the single biggest red flag in this entire article. It is the phoenix pattern: the company takes deposits, runs into trouble, folds owing money to clients and suppliers, and reappears the following month under a new name with the same people. Nothing you have signed survives the dissolution.

Then three more, all quick:

• Directors disqualification register (gov.uk). Free, searchable, tells you whether a director has been disqualified and why.
• County Court Judgments. TrustOnline, run by Registry Trust, is the official register. A search costs a few pounds. Judgments against a builder mean somebody has already had to go to court to get paid or to get a defect put right.
• VAT number. If the quote adds VAT, check the number on the gov.uk "check a UK VAT number" service. A builder charging you 20% VAT while not being VAT registered is simply keeping it.

If they are a sole trader there will be no Companies House record, and that is not in itself a problem — plenty of excellent small builders operate this way. But it does mean there is no company to hide behind and no accounts to look at, so the insurance and reference checks below carry more weight, and you want the insurance to be in their exact trading name.

Part 2: Insurance — the checks almost nobody actually does

Every builder will tell you they are fully insured. Most will produce a certificate. Very few homeowners do anything with it.

There are three policies that matter:

Public liability. Covers injury to other people and damage to their property — your neighbour's roof, a passer-by, the party wall. Not legally compulsory, but no competent builder is without it. £1m is a common level and is not enough for a substantial project on a London terrace; £5m is the level to expect on anything into six figures.

Employers' liability. This one is compulsory by law if they employ anyone, including many labour-only subcontractors, under the Employers' Liability (Compulsory Insurance) Act 1969. The statutory minimum cover is £5 million. If a builder with a team on site cannot produce this, walk away — they are committing an offence, and it tells you what else they are cutting.

Contract works, sometimes called contractors' all risks. This covers the works themselves while they are being built — fire, flood, storm, theft of materials, vandalism. It is the policy most often missing, and the one whose absence hurts you most. If a half-built extension burns down and nobody has contract works cover, the argument about who pays to rebuild it is long, expensive and often unwinnable.

(Professional indemnity is only relevant if the builder is also doing design work. If they are producing the drawings as well as building from them, ask.)

Now the part that actually matters. Do not accept a PDF certificate and file it. Certificates are trivial to fake and routinely out of date — a policy cancelled for non-payment leaves the certificate looking exactly as valid as it did the day it was issued.

Instead: take the insurer's name from the certificate, find that insurer or broker's telephone number on the insurer's own website — not the number printed on the certificate — ring them, and ask them to confirm three things. That the policy is currently live. That it is in the exact legal name of the company you are contracting with. And what the cover levels are. It takes five minutes and it is the single most useful phone call in this whole process.

While you have the certificate in front of you, check the contract works policy names the right thing. Some cover only the new work; some cover the existing structure too. On a renovation inside an existing house, that distinction is the whole point.

And then ring your own insurer. This is the step homeowners miss most often. Almost every buildings policy restricts or excludes cover during structural work, and many are void entirely if the house is unoccupied for more than 30 days. Notify your insurer in writing, describe the works honestly, and get their response in writing. If you are moving out, you may need a specific unoccupied or renovation policy. Discovering this after a burst pipe is a bad way to discover it.

Part 3: Accreditation — what is meaningful and what is decoration

There are two very different kinds of badge, and they are not equally useful.

Statutory and competent person schemes are real and checkable. Gas work must be done by someone on the Gas Safe Register — this is a legal requirement, not a nicety. Notifiable electrical work under Part P needs a registered electrician (NICEIC, NAPIT, ELECSA). Replacement windows need FENSA or CERTASS. Each of these has a public register. Look the business up on the scheme's own website using their registration number.

Trade bodies are useful but softer. The Federation of Master Builders, TrustMark and the National Federation of Builders all vet members at the point of joining and set standards of conduct. TrustMark is government-endorsed and requires a written contract. That is worth something, and members do have a complaints route you would not otherwise have. But membership is a filter, not a guarantee, and it does not remove the need for anything else in this article.

The rule for both: a logo on a website is not membership. Anyone can put an FMB or Gas Safe logo in their footer. Get the registration number and check it on the scheme's own register. It takes two minutes, and finding a logo that does not check out tells you everything you need to know before you have spent a penny.

One more distinction worth understanding. A guarantee from the builder is worth precisely as much as the builder's continued existence — which, given the strike-off rate in construction, may be less than you think. An insurance-backed guarantee is underwritten by a third party and survives the company folding. If a long guarantee is part of why you are choosing someone, ask which of the two it is, and ask to see the policy.

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Not sure whether what you are looking at stacks up? Send me the quotation and I will read it properly — what is excluded, what is a provisional sum dressed up as a price, and what I would want answered before anyone signs. No charge and no obligation. Email [email protected] or call me on 07525 474 849.

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Part 4: Evidence that they can actually do your job

Photographs prove nothing. Anyone can have photographs.

Ask for three addresses, not three pictures — projects of comparable scale and type, completed in the last two years. A builder who does excellent kitchen refits may never have managed a structural opening or a party wall, and a loft specialist may be out of their depth on a whole-house renovation. You want evidence of your job, not of building work in general.

Then go and look at one. And speak to the homeowner without the builder present. The questions that actually produce useful answers:

1. Did the final invoice match the original quotation? If not, by how much, and why?
2. How were variations and extras handled — priced and agreed in writing before the work, or added at the end?
3. How far over the original programme did it run?
4. When something went wrong, how did they behave?
5. Were the same faces on site every day, or did the team keep changing?
6. Did they come back to deal with the snagging list?
7. Would you use them again?

That last one matters most, and what you are listening for is not the answer but the pause before it. An unhesitating yes is worth a great deal. A carefully constructed "well, on balance…" is worth even more, and you should ask what is behind it.

Also ask to see a job in progress. A live site tells you things a finished one cannot: whether it is tidy and safe, whether materials are being looked after, whether anyone is actually there. And ask directly how much of your job will be subcontracted and to whom. There is nothing wrong with subcontracting — every builder does it — but "we do everything in house" from a firm of three people is not true, and you want to know who is really going to be on your roof.

Part 5: The commercial checks

The deposit. A reasonable builder may ask for a payment to cover materials ordered up front. What is not reasonable is a large deposit before anything has happened. Anything above roughly 10 to 15 per cent, or any request to pay into a personal rather than a business account, deserves a hard question. Deposits taken and never worked against are the most common way homeowners lose money outright.

Stage payments against completed work, never against dates. "£20,000 on 1 October" pays for the calendar. "£20,000 on completion of the roof structure, inspected and agreed" pays for the building. Keep the payments slightly behind the work at every point. The moment you are in credit you have lost every piece of leverage you had.

Retention. Hold back 2.5 to 5 per cent for six to twelve months after completion. It is the only thing that reliably brings a builder back to fix the things that emerge in the first winter.

Verify the bank details by phone. Invoice redirection fraud is rife in construction — a convincing email arrives saying the account has changed, and six figures goes somewhere else entirely. Ring a number you already had, speak to someone you have already met, and confirm. Do it every time the details change.

Part 6: Before you sign

Always a written contract. Not a quotation with a signature at the bottom. The JCT Home Owner contracts and the FMB's building contract are both written for domestic work and both are far better than nothing.

What has to be in it: the scope of work, with drawings referenced by revision number so everyone knows which version is being built. The exclusions, spelled out. Every provisional sum listed as such. Start and completion dates. A written variation process — how a change gets priced and agreed before it is carried out. The payment schedule. The retention. A defects liability period. Each party's insurance obligations. And a route for resolving a dispute that is not the county court.

The 14-day cancellation right nobody mentions

This is worth knowing and very few homeowners are told about it.

If you agree a building contract at your home — which is how nearly all of them are agreed — it is an off-premises contract under the Consumer Contracts (Information, Cancellation and Additional Charges) Regulations 2013. That gives you 14 days to cancel, running from the day after the contract is made.

Three things follow from that:

• The trader is required to tell you about this right in writing. If they do not, the cancellation period is extended — potentially by up to 12 months.
• If you want work to start inside the 14 days, you have to request it, and it is worth doing so in writing. If you then cancel, you pay proportionally for the work already done.
• A builder who reacts badly to you saying "I would like to take my fortnight before we start" has told you something important about how they will react to everything else.

Alongside this, the Consumer Rights Act 2015 requires any service to be performed with reasonable care and skill, within a reasonable time, and for a reasonable price where none was agreed. Those rights cannot be contracted away, whatever the small print says.

(This is general information rather than legal advice — for anything contentious or high-value, take advice from a solicitor.)

The red flags, in one list

• A trail of dissolved companies behind the same directors
• Overdue accounts or a strike-off notice at Companies House
• Reluctance to give the full registered company name and number
• An insurance certificate they would rather you did not verify with the insurer
• No employers' liability where there is clearly a team
• No contract works cover
• Accreditation logos with no registration number behind them
• References that are all photographs and no addresses
• A large deposit, wanted quickly, ideally today
• A price significantly below the others, with a discount for signing now
• Vagueness about which parts are subcontracted
• Any resistance at all to a written contract
• Irritation at being asked any of the above

That last one is the real test. Every check in this article is routine and reasonable, and a good builder has been asked all of it before. The reaction to the questions is often more informative than the answers.

The honest summary

All of this takes about a day and costs less than £50. Set that against a project of £150,000 or £300,000 and it is not a close call — and yet the majority of homeowners do almost none of it, because at the point of choosing a builder you are tired of the process and you want to get on with it.

That is exactly the moment the checks matter most.

If you would rather someone else did this

Vetting builders, reading quotations line by line and getting the contract into a state worth signing is a large part of what I do for homeowners across South West London — before a builder is appointed, when everything is still changeable and mistakes are still cheap to fix.

Send me your builder's quotation and I will tell you what is missing. No charge, no obligation, and if the quote is sound I will tell you that too.

• Call or text: 07525 474 849
• Email: [email protected]
• Or send the details here: homeownersprojectmanager.co.uk/contact

You do not need drawings, a builder or a budget to get in touch. If what you actually need is an architect, a structural engineer or simply a different builder, I will say so and point you towards the right person.

Related reading: how to compare builder quotes without missing hidden costs, 12 questions to ask before hiring a renovation project manager, the most common renovation budget overruns and what a project manager costs. You can also see projects I have run.

General guidance, correct as of August 2026. Registers, schemes and regulations change — always check the current position, and take professional advice on anything contentious.