How to choose a builder in London?

Everyone has a dodgy builder story , and we have heard more than our fair share.

A major renovation, extension or loft conversion is one of the biggest investments you’ll make in your home. Choosing the wrong builder doesn’t just cost money; it costs time, peace of mind and in the worst cases, years of stress to unpick.

So how do you choose the right builder in London? It starts with asking the right questions before you sign anything.

We’ve put together the 10 essential questions to ask when hiring a builder for a renovation, extension, loft conversion or any home renovation project across London. Whether you’re in the early stages of planning or ready to get quotes, these questions will help you vet any contractor with confidence and spot the red flags before they become expensive problems.

Prefer a more visual read? Browse the interactive guide below or scroll down for the full article.

Ask your potential builder these 10 questions

1. Can you show evidence of similar projects you’ve completed in size, complexity, and quality to mine?

Builders have different specialisms. If you live in a period property (as many London homes are), you will want to make sure they’ve worked on similar.

Experience in new builds doesn’t translate to older houses. Retrofitting heating, plumbing, or structural changes in a 200-year-old property is very different from a modern build. So, while this is not a knock on the builder if they haven’t worked on similar, it may be a sign that they might not be the right fit for this job.

Top tip: Ask for photos, drawings, and if possible a site visit or a past client you can speak to. If visiting a live job, look at site management, communication and professionalism. Ask former clients about budget, handling unexpected issues, and snagging follow-ups.

Note: Speaking to previous clients isn’t always possible and can be a hassle for homeowners who have been asked multiple times, so only pursue this for builders you’re seriously considering.

2. How do you price work and what are your labour rates and overheads based on?

You are not looking for the cheapest number, but clarity on how the price is built. Don’t accept a a top-line estimate.

A fixed-price quote shows commitment. And it should be detailed. It should break down all stages of work (foundations, structure, roof, electrics, plumbing, plastering) and clarify what materials are included. It should also identify what you need to supply, for the avoidance of doubt further down the line.

3. Can you confirm financial stability and official payment methods?

No one wants a builder with a shaky financial record. Do a quick Companies House search for stable trading history (ideally 5+ years) and check directors’ backgrounds. Watch out for phoenixing; a name given to companies that close and restart repeatedly.

4. How do you handle money, deposits, stage payments and variations?

A good builder can explain this clearly. Payments should be staged, tied to completed work, with a deposit no larger than 10 to 15%. Never pay upfront for work not yet done or materials not delivered. And never accept cash-only payments to “avoid VAT” – it leaves you unprotected and suggests legal issues.

5. Can I see your standard terms of business before we proceed?

This shows how disputes, variations, delays and payment are handled, not just how the job starts. Ask how they manage variations, whether from changes you request or unexpected site issues.

Extra tip: Keep this one in mind for later. Check that their contract includes a Defects Liability Period, usually 3–6 months after completion, when the builder must return to fix any minor snags or defects

6. What accreditations, insurances and certifications do you currently hold?

Ask for details of the contractor’s current Contract Works Insurance and a valid certificate showing the types of work covered. You should also check they hold Public Liability and Employers’ Liability insurance, along with any relevant certifications such as FMB, Gas Safe, or NICEIC/ELECSA. This helps protect you, your property, and everyone working on site.

7. How do you approach problems when something unexpected comes up on site?

If something unexpected comes up on site , as it often can, you’ll want to know how the builder assesses and handles it. How do they explore practical solutions, and how do they communicate with you? Asking for a real-life example helps reveal problem-solving skills, accountability and professionalism. It also signals confidence and experience in handling issues calmly, without panic or blame.

8. How do you ensure clients feel confident and satisfied throughout a project?

This question helps you assess whether a builder takes a sense of pride in their work. The answer can reveal how they maintain high standards, handle challenges, and communicate throughout. Those who are proactive, transparent, and attentive show they care about how their work is perceived and its long-term impact so you can identify builders invested in delivering a thorough, reliable, and professional job, This question and it’s answer speaks volumes to their reputation.

9. Who will be responsible for my project day to day, and how will we communicate?

Find out exactly who your single point of contact will be (the Project Manager) and how often you will get updates. Lack of communication is a top complaint from London homeowners when it comes to building work so find out how they’ll communicate and decide if that’s how you would like to work.

Know whether they use employees or subcontractors. Subcontractors are normal for specific skills (electricians/ plumbers/ heating technicians), but they must be insured and vetted.

You want to ensure that you agree on working hours that respect your neighbours (especially in densely packed London terraces) and these should include procedures for noise management.

Discuss how they would manage access, where materials will be stored, and how they will manage waste (e.g., daily clean-up, location of the skip).

All of this reflects their professionalism and attention to detail.

10. Why do you want to work on this project specifically?

This question helps you understand a builder’s motivations and whether they see you as a partner or just another job. A good answer will show genuine interest in your home, the type of work involved and how they can add value beyond simply building what’s on the plans.

They should be asking thoughtful questions and showing signs they’ve taken time to understand your brief, budget and priorities. Builders who are motivated by the right projects tend to price more carefully, communicate more openly and stay engaged when challenges come up. If the answer feels rushed, vague or focused only on filling a gap in their schedule, it can be a sign they’re not fully invested in your project.

Working with a builder who wants to work with you rather than just for you can set the tone for a more collaborative and successful project from day one.

Final thoughts

The goal of these questions isn’t to catch a prospective builder out.

It’s to help you choose based on evidence, not promises by someone telling you what you want to hear.

By looking for insurances, accreditations, transparent pricing, relevant experience, good money handling, a real reputation to protect, and values that align with yours; you dramatically reduce risk from the start.

Once you’ve shortlisted one or two builders who meet these standards, asking them to price in detail becomes far more effective. You’ve filtered out the cowboys, protected your project, and given good builders the confidence and motivation to engage properly, price carefully, and work with you as true partners in your project.

Good luck bringing your home project to life!

Want to see what the top questions that we would ask when choosing an architect? Check out our guide Your guide to choosing the right partner for your home plus 15 essential questions to ask before you decide.