How to Vet a Builder Before You Hire One

Title: How to Vet a Builder in London: 10 Things to Check Before You Hire Target keyword: how to vet a builder London

Choosing the wrong builder for a loft conversion or extension is expensive and stressful to undo. The good news is that most of the red flags are visible before you sign anything — if you know what to look for.

Here are 10 specific checks to run on any builder before committing.

1. Are They on a Quality Scheme?

Look for registration with:

FMB (Federation of Master Builders): Independent vetting, inspection of past work, reference checks, and dispute resolution. One of the strongest marks of quality in UK residential construction.
TrustMark: Government-endorsed scheme covering quality, compliance, and consumer protection. Search at trustmark.org.uk.
Checkatrade or TrustATrader: Not as rigorous as FMB but useful — reviews are verified, and there's a complaints process.

A builder who says they "don't need" accreditation isn't necessarily bad — but accreditation protects you, not them.

2. Can They Show You a Completed Project?

Ask for a recently completed project — same type as yours — that you can visit or at least see detailed photos of. Better still, speak to the previous client directly. A genuine contractor with good work to show will welcome this.

Be cautious of builders who only show renders or early-stage photos. What matters is the finished quality.

3. Are They Insured?

For residential construction, the minimum insurance requirements are: - Public Liability: Minimum £2 million for projects under £100,000; minimum £5 million for larger projects - Employers' Liability: Minimum £10 million (legal requirement if they have employees)

Ask for a copy of the insurance certificate — not just confirmation that they have it. Check the policy is current and covers the type of work you're commissioning.

4. Do They Offer a Proper Contract?

Any competent contractor should be willing to enter into a written contract. Common residential contracts include JCT Minor Works or Homeowner contracts. At minimum, the contract should set out: - Scope of works - Payment schedule (never pay all upfront) - Start and completion dates - Variation procedure - Retention

A builder who refuses to sign a contract is a significant red flag.

5. What is Their Payment Schedule?

A standard residential payment structure for a loft conversion might be: - 10% deposit on signing - 20% at frame/structure stage - 25% at first fix - 25% at second fix - 15% at practical completion - 5% retention released after snagging

Never pay more than 10–15% upfront. Never pay a final invoice in full before the snagging list is signed off. A contractor who demands a large upfront payment before starting is a warning sign.

6. How Do They Handle Variations?

Ask specifically: "If we want to make a change to the original scope during the build, what's your process?" A competent contractor will describe a written variation order process with agreed pricing before proceeding. One who says "we'll sort it out at the end" creates the conditions for disputes.

7. Who Will Be On Site?

Some contractors win work, then subcontract 100% of it to others you've never met. Ask who the site supervisor is and how often they'll be on site. Understand whether the skilled trades (carpenter, plumber, electrician) are employed directly or subcontracted, and whether the contractor supervises them or leaves it to chance.

8. Can They Provide References for Similar Projects?

Ask for three client references for similar projects — loft conversions if you're doing a loft conversion, extensions if you're doing an extension. Call them. Ask not just "were you happy?" but: "Were there any issues during the project? Were variations handled fairly? Did the programme slip, and if so, how was it managed?"

9. What is Their Principal Contractor Experience?

For any project over £500,000 in value, or any project with more than one contractor on site simultaneously, CDM 2015 applies and a Principal Contractor must be appointed. Even for smaller projects, a contractor with Principal Contractor experience understands sequencing, coordination, and compliance — making them significantly less likely to cause problems.

10. How Do They Communicate?

In the qualification and sales process, is the contractor responsive, organised, and clear? Do they show up when they say they will? Do they produce documents (quotes, scopes of work) that are clear and professional? The way a contractor communicates before you sign is usually a good indicator of how they'll communicate during the build.

At RCB Design & Build, we welcome every one of these checks. We carry FMB, TrustMark, Checkatrade, and TrustATrader accreditation. We use proper contracts and structured payment schedules. We can show you completed work and connect you with previous clients.

Call 07359 872594 or visit rcbgroup.co.uk to start the conversation.