How to Choose a Builder in London: Complete Guide
How to find, vet, and hire the right builder for your extension. Avoid cowboys, understand contracts, and protect your investment.
Key Points for Choosing a Builder
- Get 3-5 quotes: Compare like-for-like from detailed specifications
- Check references: Visit at least 2 completed projects in person
- Written contract: Essential—covers scope, price, timeline, payment terms
- Get instant cost estimate before approaching builders (Free)
Choosing the right builder is one of the most important decisions you'll make for your extension project. A good builder delivers quality work on time and budget. A bad one can cause stress, delays, cost overruns, and poor workmanship that affects your home for years.
Where to Find Builders
Personal Recommendations
Best source. Ask neighbours, friends, colleagues who've had similar work done. You can see the finished quality and ask honest questions.
Architect Recommendations
Your architect or designer will have builders they've worked with before. They know who delivers quality and who to avoid.
Trade Associations
Federation of Master Builders (FMB), TrustMark, Checkatrade. Membership requires vetting and provides some consumer protection.
Local Building Projects
See skips or scaffolding nearby? Ask the homeowner how their builder is performing. Builders working locally reduces travel costs.
Vetting Checklist
Getting Quotes
Get 3-5 quotes minimum. Ensure all builders are quoting from the same specification—ideally detailed drawings and a schedule of works from your architect.
| Quote Element | What to Check |
|---|---|
| Fixed price vs estimate | Fixed is safer; estimates can increase |
| What's included | Skip hire, scaffolding, building control fees? |
| Payment schedule | Stage payments, not large upfront deposits |
| Timeline | Start date, duration, completion target |
| Variations process | How are changes priced and agreed? |
Red Flags to Avoid
Large Upfront Deposits
Never pay more than 10-15% upfront. Stage payments should match work completed.
Cash Only
Reputable builders accept bank transfers. Cash-only suggests tax avoidance.
No Written Quote
Everything should be in writing. Verbal agreements lead to disputes.
Pressure Tactics
"Price only valid today" or "I have another job waiting" are pressure tactics.
Unusually Cheap Quotes
If one quote is 30%+ cheaper, they've either missed something or plan to cut corners.
No Insurance Proof
Ask to see current insurance certificates. If they won't provide them, walk away.
Contract Essentials
Use a proper building contract. The JCT Minor Works or FMB contract are industry standards that protect both parties.
- Scope of works: Detailed description of all work included
- Contract sum: Fixed price with clear variation process
- Payment terms: Stage payments linked to milestones
- Start and completion dates: With provisions for delays
- Defects liability: Typically 6-12 months to fix issues
- Retention: Hold back 2.5-5% until defects rectified
- Dispute resolution: Adjudication or mediation clause
Know Your Extension Costs First
Get an instant cost estimate before approaching builders, so you know what to expect.
Frequently Asked Questions
How much deposit should I pay?
Maximum 10-15% upfront for materials ordering. The rest should be stage payments as work progresses.
Should I use the cheapest quote?
Rarely. Understand why it's cheaper. Usually middle quotes from well-referenced builders offer best value.
What if things go wrong?
Document everything in writing. Use your contract's dispute resolution process. Citizens Advice and trading standards can help with serious issues.
How long should I expect to wait for a good builder?
Good builders are in demand. Expect 2-6 months wait for established contractors. Plan ahead and get quotes early.