How to Choose a Builder in London: Questions to Ask, Insurance and Accreditations
Choosing a builder in London comes down to evidence. You want to see proof of experience, proper insurance, a clear written quote and a contract that protects both sides. This guide gives you a practical checklist of what to ask and what to look for, so you can compare firms on facts rather than just price or charm.
Check the credentials
Start with experience that matches your project
Ask whether the builder has done work like yours, such as a loft, extension or full refurbishment, and for how long. Look for a portfolio of real projects and, where possible, speak to previous clients or visit a completed job. Check how long they have been trading and whether they have in-house tradespeople, such as joiners, or rely entirely on subcontractors. At TNK we have 17+ years' experience and over 150 projects, and our builders and joiners are CITB-accredited.
Check insurance, not just the claim
Do not take "fully insured" on trust. Ask to see certificates and check the cover is current. Typically you would look for:
Public liability insurance: covers damage to third parties and their property.
Employer's liability insurance: needed if the firm employs people.
Contract works insurance: covers the building work itself, in some cases arranged by the homeowner or the builder, so agree who is responsible.
Also tell your own home insurer about the project, because your policy may be affected during building work.
Understand accreditations and trade schemes
Accreditations vary in what they prove, so ask what each one means. Examples include CITB-related training and cards, membership of trade bodies, and competent person schemes for electrics and gas. Check them on the issuing body's own register where possible. A badge on a website is not the same as verified status.
Questions to ask every builder
Can you provide references and examples of similar work?
Who will manage my project day to day, and who will be on site?
Is your quote itemised, and what is excluded?
How do you handle variations and extra costs?
Which approvals will you arrange, such as building control and Party Wall notices?
What is your payment schedule?
What guarantees or warranties do you offer for completed work?
What is your programme, and what could delay it?
Clear, patient answers are a good sign. Evasiveness is not.
Get it in writing
A professional contract should set out scope, price, payment stages, start and finish dates, how changes are handled and what happens if something goes wrong. Be cautious about large upfront payments. Staged payments tied to completed progress are fairer for both sides. Ask for a detailed specification so that "supply and fit" items do not become arguments later.
Compare quotes properly
Lay quotes side by side and compare scope, not just the total. A cheap figure with provisional sums, exclusions or vague allowances can end up costing more. If one quote is dramatically lower than the rest, ask why. Our cost calculator can help you sense-check the ballpark before you request formal prices.
Warning signs to watch for
Pressure to pay a large deposit or cash upfront.
A quote that is a single line with no breakdown.
No physical address, no previous work to see and no references.
Reluctance to put anything in writing.
Starting dates that keep slipping before you have even signed.
It is also worth arranging a site visit before any price is given. A builder who measures up, looks at the structure and asks questions about how you live is far more likely to give an accurate figure than one who quotes from a phone call. Take notes on how clearly they explain the process, because that same communication will matter throughout the build.
Finally, trust your instincts about the relationship. You will be sharing your home with this team for weeks or months, so choose people who listen, answer questions directly and treat your property with respect. A builder who is happy to explain, in plain English, why something costs what it does is usually one worth talking to again.
A final tip is to ask how the builder deals with problems. Every project meets one, and the way a firm responds tells you more than any brochure.
Frequently asked questions
Should I always pick the cheapest quote?
No. Look at what is included, the builder's track record and how clear their communication is. The right choice is usually the best value, not the lowest figure.
How many quotes should I get?
Three is a common starting point, provided each is based on the same drawings and specification.
Do I need a written contract for a small job?
Yes. Even a short, clear document protects you and the builder.
Speak to TNK
If you are planning a loft conversion, an extension or a refurbishment, we would be glad to answer these questions for your project. Get in touch to arrange a visit and an itemised quote.
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