What Questions Should I Ask a Builder Before Hiring in London?

Disqualify them and move to the next candidate. A legitimate London builder is accustomed to credibility questions and welcomes them as a basis for trust and contract. Builders who deflect, claim 'we don't share that information' or push hard to sign before answering are either inexperienced, hiding something or dealing with high client churn from previous disputes. The cost of asking twelve questions and walking away from a candidate is hours; the cost of signing with a problem contractor is months and tens of thousands of pounds.

Yes, and always speak by phone. Email references are easy to fabricate. Phone calls reveal subtle dissatisfaction that written references hide. Ask each reference five questions: did the project complete on the original timeline or did it overrun and by how much; did the final cost match the original quote or did variations add cost beyond the quote; how was communication during the build; how were defects handled at completion and during the warranty period; would you use this builder again and why. References that hedge on 'would you use them again' are the most informative — that hesitation reveals the issues the reference is being diplomatic about.

The core 12 questions are identical regardless of project size. What differs is the depth of investigation appropriate to each. On a £20,000 project: phone references, verify insurance via certificate sighting, accept a single-page contract supplement to a written quote. On a £200,000 project: site visit to a completed reference, verify insurance via the broker not just the certificate, JCT Minor Works or Intermediate Building Contract with solicitor review, named project manager attending fortnightly meetings, independent chartered building surveyor representing you. The £20,000 project takes 8-12 hours of vetting; the £200,000 project takes 25-40 hours of vetting plus £2,500-£8,000 in professional fees. Vetting effort scales with project size and consequence.