How to Find a Builder You Can Trust for an Extension (Without Getting Burned)

Nearly half of UK homeowners think builders are licensed. They aren't. There is no register you can strike a bad builder off, no exam they have to pass, no card they have to carry. Anyone can print "builder" on a van tomorrow morning and take your deposit by the afternoon. A 2025 survey of 2,051 adults by the Federation of Master Builders and the HomeOwners Alliance put a number on the damage: 37% of us have hired an unreliable or unqualified builder, and rogue trades have cost homeowners a cumulative £14.3 billion over five years.

Search "how to find a builder" and most of what you read is written by companies that want to sell you leads. A directory earns money when you click through and book, so its advice stops conveniently short of "here's how our own vetting can miss things." What follows is the homeowner's view instead, grounded in a real 30m² kitchen extension in Oxfordshire that came in at £120,000 of construction cost and taught its owner most of these lessons the expensive way.

Why There Is No Builder Licence in the UK

Plumbers touching gas need to be Gas Safe registered. Electricians doing notifiable work in England and Wales fall under Part P. But the person coordinating your entire build, pouring your foundations and dropping a steel beam over your kitchen, needs no qualification at all. That gap surprises people, and it should.

Your baseline protection comes from the Consumer Rights Act 2015, which says work must be done with reasonable care and skill, within a reasonable time, for a reasonable price. Useful in a dispute, useless as a filter. It gives you a claim after things go wrong; it does nothing to stop you hiring the wrong person in the first place.

The FMB has been campaigning for a "Licence to Build," and Mark Garnier MP's Domestic Building Works Consumer Protection Bill would introduce mandatory licensing if it passes. Its second reading is not due until early 2027, and a second reading is a long way from law. So plan for the world as it is: no licence exists, and the vetting is entirely your job.

37%

Share of UK homeowners who have hired an unreliable or unqualified builder, per the FMB and HomeOwners Alliance 2025 survey of 2,051 adults. Of those hit, 15% reported a direct financial loss averaging £1,758.80 each.

Where to Actually Look

Start with people you know. A neighbour whose extension went well is worth more than any directory, because you can stand in the finished room, ask what the builder was like when a problem hit, and get an unguarded answer. Most people don't have a ready recommendation, though, so you'll end up on the platforms. They are not equal, and the differences matter.

The Federation of Master Builders runs the closest thing to a vetted shortlist. New members face reference checks, credit and director checks, and an independent on-site inspection, and they are re-inspected every three years. Checkatrade does a face-to-face vetting visit and rings five references before listing a trade. MyBuilder lets you post a job and field approaches, which casts the widest net but does the least filtering. Rated People is lighter still: it runs an Equifax or Experian identity and credit check plus an Action Fraud and TrustMark legitimacy check, with no in-person interview and no reference calls. Its real strength is a closed-loop review system, where only homeowners who booked through the platform can leave a review, which cuts down (without eliminating) planted ratings. That is the opposite of an open review site, where anyone can post.

TrustMark works differently again, and it's worth understanding because the badge is widely misread. TrustMark doesn't vet individual builders. It accredits around 38 Scheme Providers who do the vetting, covering roughly 17,500 businesses across 156 trades, and it mandates Insurance-Backed Guarantees on deposit-protected work so the warranty survives even if the firm folds.

The one almost nobody mentions is Buy with Confidence. It's run by Trading Standards rather than a commercial platform, covers 60-plus local authorities, and vets on references, complaint history and ongoing monitoring. Coverage is patchy council by council, so check whether yours takes part, but as a non-commercial signal it carries real weight.

Use these to build a longlist, not a shortlist. Every name that comes off a platform still gets your own reference checks. The finding a reliable builder task in the kitchen extension tree walks the full sourcing-to-appointment sequence, including the site-visit checklist and the questions to put to every candidate. This post is about the judgement calls the checklist can't make for you.

Which Accreditations Actually Matter

Builders collect logos. Homeowners assume every logo means the same thing. It doesn't, and sorting them into three tiers is the single most useful thing you can learn here.

Legally mandatory. Gas Safe registration for any gas work, and Part P competence (through NICEIC or NAPIT) for notifiable electrical work in England and Wales. These carry statutory weight. If your extension involves a new gas run or a consumer unit change, the person doing it must be registered, and you can check the register yourself in two minutes. Scotland and Northern Ireland run their own electrical regimes, so Part P is not a UK-wide test.

Commercially useful, not mandatory. FMB membership, TrustMark Scheme Provider accreditation, and structural warranty schemes like MasterBond. None is required by law, and none guarantees a good build. What they give you is a firm that has cleared a credit check, holds insurance, and has something to lose from a complaint. Treat them as positive signals that still need your own reference checks behind them.

Largely irrelevant to you. CHAS is the one to stop over-weighting. It certifies a contractor's health-and-safety management systems, which matters for public-sector and commercial tendering, not for whether your kitchen extension gets built well. Around 80% of first-time applicants fail it, usually on safety paperwork, so a builder who holds it has jumped a real hurdle. It just isn't a hurdle that tells you anything about the quality of their brickwork.

The Near-Misses That Teach the Lesson

Vetting questions sound abstract until you've watched what happens when nobody asked them. Three moments from the documented Oxfordshire build map straight onto questions you can ask before signing anything.

The steelwork saga. Partway through the build, the structural engineer's drawings and the main contractor's on-site measurements disagreed over a rafter bearing and the ridge beam specification. Resolving it took multiple rounds between the steel fabricator, the engineer and the contractor, and the ridge beam was eventually re-specified and partly re-fabricated. That single dispute was the biggest driver of a timeline that stretched to an outlier 35 months, against the 9 to 15 a well-run equivalent takes. The vetting question it hands you: "How do you handle changes to the agreed scope?" A builder who prices variations in writing before doing the work, the way the JCT Home Owner Contract's structure assumes, is a builder who won't turn a measurement clash into a month of standing still.

The unauthorised spec change. On the same build, the contractor quietly fitted a timber ridge beam where the structural design called for steel. Nobody was told. It surfaced only when building control inspected. No insurance policy prevents that; only a written contract and an engaged homeowner do. The question: "Who signs off structural changes, and how will I know one has happened?"

Supplier failure and stage-payment friction. A materials supplier missed a promised delivery at a critical point, and no-show trades were a low-grade friction across the whole build. Ask a prospective builder how they manage supplier lead times and whether a supplier has ever let them down. A builder who says "never" is either very lucky or not being candid. Ask, too, how they structure payments, because the answer tells you whether they expect to be paid for work done or work promised.

References You Actually Check

Anyone can hand you a list of happy names. The point is what you do with it.

Ask to see a completed extension of comparable size, ideally finished in the last year and nearby. Stand in it. A finished job tells you about finish quality, how the new structure meets the old house, and whether the details were done properly or rushed. Then ask to speak to that homeowner without the builder in the room, and ask the questions that get honest answers: Did it finish when they said? What did the final bill do against the quote? Were there extras, and were they warned before the work happened or invoiced after? Would they use them again, and can they say that without hesitating?

If you can, ask to see a job in progress too. A tidy, well-organised site with the right protection down is a different signal from photographs on a website. It shows you how this builder works when they think a client isn't watching.

Insurance and Warranties, Briefly

Three covers matter, and none of them protects you the way you'd assume. Public liability covers damage the builder negligently causes, at £2,000,000 minimum and ideally more on structural work. Employers' liability is legally required if they have staff or labour-only subcontractors. Contract works cover protects the half-built structure itself against fire, storm and theft, and the builder often doesn't hold it. On top of the builder's cover, a structural warranty or Insurance-Backed Guarantee protects you if the firm ceases trading. All of this deserves proper attention before the start date, and it gets it in the companion guide to whether your builder needs insurance. Verify the certificates, match the named insured to your contract, and phone the insurer using details you find yourself.

Getting Your Contract Right

Most extension disputes come down to a handshake where a document should have been. The fix is cheap and specific: the JCT Home Owner Building Contract (HO/B), which costs roughly £30 to £40 to buy, carries the Plain English Campaign's Crystal Mark, and includes a fast-track Adjudication clause giving you a binding decision from an independent adjudicator within 28 days. That is a genuine alternative to a slow, expensive court fight, built into a contract a homeowner can read without a solicitor. It is not suitable for use in Scotland, which has its own arrangements.

Whatever contract you use, the payment principle is fixed. Stage payments must be tied to completed, verified stages, never to calendar dates. "£15,000 on the first of each month" pays a builder for time; "£15,000 when the roof is watertight and inspected" pays them for a finished stage you can stand under. A 10–20% deposit is normal; a deposit in the 20–25% range needs a clear justification like pre-ordered steel or glazing; anything above 25% is a red flag whatever the excuse.

Red Flags

Read these when you're calm, because in the moment, keen to get moving, you will rationalise every one of them away.

• Cash-only, or pressure to pay "VAT-free". You lose your paper trail and, if it's over £100, your card protection.
• No fixed business address, or a company name on the van that isn't on Companies House.
• Pressure to start immediately or decide by Friday. Good builders are booked months ahead and can wait for you to check them out.
• No written quote. A price agreed over coffee is a conversation, not a commitment.
• Vague scope. "Build the extension" is not a specification. You want line items and clear exclusions.
• Being told you "won't need planning or building control." Sort those yourself; a builder who waves them away is telling you how they work.
• Doorstep cold-calling, and an unrealistically fast start date from a busy trade.

Any one of these earns a pause. Two together, walk.

If It Goes Wrong

Sometimes the vetting holds and the build still sours. The dominant pattern in homeowner forums is the same story told again: a deposit paid in good faith, site presence tailing off, one more request for money "to buy steel", then silence. One homeowner on MoneySavingExpert had paid £60,000 in staged payments, was seeing the builder on site less and less, paid a further lump sum for steel out of desperation to keep things moving, and lost that too.

The recovery ladder is predictable, so know it before you need it. Start with a formal letter by recorded delivery, referencing your contract, setting a clear deadline (14 days is the forum convention) to return money or resume work. If that fails, the Small Claims route through Money Claim Online handles most domestic disputes, with High Court Enforcement available for larger sums once you have judgment. Payment method decides how realistic recovery is: a card payment may unlock Section 75 or chargeback, while cash, cheque and bank transfer leave the courts as your only road, and a judgment against someone with no assets is a piece of paper.

Which is why the prevention is worth more than any remedy. Never let cumulative payments run ahead of the work actually completed and verified on site. Pay for work done, not work promised. Every horror story in the research breaks that one rule.

The Short Version

There is no licence, so the vetting is yours. Recommendations first, then the platforms, understanding that each checks something different. Sort the accreditations into what carries legal weight, what's a useful signal, and what's irrelevant to you, and verify every claim with the issuing body. Visit finished jobs, speak to those homeowners, and read the answers between the lines. Sign a proper contract, tie every payment to a completed stage, and keep your money one step behind the work rather than one step ahead of it.

Do that and you won't eliminate the risk, because no homeowner can. You'll stack it heavily in your favour, which is the whole game. The finding a reliable builder task lays out the full systematic walkthrough, checklists included, and the structure of the whole kitchen extension guide is free to browse.

Frequently Asked Questions

Are builders licensed or registered in the UK?

No. There is no statutory licence to work as a builder in the UK, which is why nearly half of homeowners are surprised to learn it. Gas work needs Gas Safe registration and notifiable electrical work in England and Wales falls under Part P, but the person coordinating your whole build needs no qualification at all. The vetting is entirely your responsibility.

What accreditation should a builder for an extension have?

Look for FMB membership or a TrustMark Scheme Provider, both of which involve credit checks, insurance and independent inspection, and Gas Safe or Part P registration for any gas or electrical work. Verify every claim with the issuing body directly rather than trusting a logo. Treat CHAS as largely irrelevant to a domestic extension, since it certifies health-and-safety systems for commercial tendering, not build quality.

How much deposit should I pay a builder for an extension?

A deposit around 10–20% of the quote is normal. A deposit in the 20–25% range needs a clear justification, such as pre-ordered steel or specialist glazing, and anything above 25% is a red flag whatever the explanation. Pay by credit card where you can, so the Consumer Credit Act protections apply.

What contract should I use for an extension?

The JCT Home Owner Building Contract (HO/B) is the standard choice for a homeowner dealing directly with a builder. It costs roughly £30 to £40, is written in plain English, and includes a 28-day Adjudication clause that gives you a fast, binding route through a dispute without going to court. It is not suitable for use in Scotland.

What do I do if my builder disappears with my deposit?

Send a formal letter by recorded delivery referencing your contract and setting a 14-day deadline to return the money or resume work. If that fails, pursue the debt through Small Claims via Money Claim Online, with High Court Enforcement for larger sums. Recovery is far more realistic if you paid by credit card, so keep every payment behind the value of completed work to limit what is ever at risk.

How many builders should I get quotes from?

Get at least three quotes on the same written specification, and five if you can. Two isn't enough to spot which price is the outlier, and more than five annoys busy builders who invest real time in a site visit and detailed pricing. Compare line by line, because the cheapest quote usually means something has been left out.