How to Choose a Reliable Builder for Your Extension or Renovation in the UK

Choosing the right builder is the single most important decision you'll make in your entire extension or renovation project. The right contractor will deliver a beautiful result on time and on budget. The wrong one can cost you tens of thousands in remedial work, legal fees, and stress. Here's how to get it right every time.

Start With Recommendations

Word-of-mouth is still the most reliable way to find a good builder. Ask neighbours, friends, or family who have had recent building work done. If you see a building site near your home, knock on the door and ask the homeowner about their experience. Genuine recommendations from people you trust are worth more than any directory listing.

Check Professional Accreditations

While not mandatory, professional memberships and accreditations provide an important layer of protection and assurance:

• FMB (Federation of Master Builders): Members are independently inspected and vetted. FMB offers a free dispute resolution service.
• NHBC (National House Building Council): The leading warranty provider for new builds and major renovations.
• LABC Warranty / Premier Guarantee: Alternative structural warranties for new builds and extensions.
• TrustMark: Government-endorsed quality scheme for tradespeople.
• Which? Trusted Traders: Independent endorsement with customer review history.

Vet Them Properly

Before inviting a builder to quote, carry out these basic checks:

1. Companies House: Check the company is registered and has been trading for at least 3 years. Review any previous company names.
2. Public liability insurance: Must have at least £2 million public liability insurance. Ask for a copy of the current certificate.
3. References: Ask for three recent references and actually call them. Visit a recent project if possible.
4. Similar project experience: Have they completed projects similar to yours? Ask to see photos of relevant work.
5. VAT registration: For projects over ~£50,000, you should expect your builder to be VAT-registered.

Getting Quotes: What to Insist On

Always get a minimum of three detailed quotes. A detailed quote should include:

• A full schedule of works — itemised, not just a total figure
• Materials specification — what brand/grade of materials are included
• Programme — a proposed start date and completion timeline
• Payment schedule — linked to milestones, not arbitrary dates
• Exclusions — what is NOT included must be clearly stated

Beware of quotes that are significantly cheaper than the others — this usually means something has been missed, cheaper materials are specified, or the contractor plans to make money on variations.

The Contract: Non-Negotiable Essentials

Never start work without a written contract. The JCT Minor Works Building Contract is widely used for domestic projects. At minimum, your contract should include:

• Scope of works and agreed specification
• Start and completion dates with provisions for extensions of time
• Agreed contract sum and payment schedule
• Variation procedure — how any changes are authorised and priced
• Defects period — typically 6–12 months post-completion
• Insurance obligations for both parties
• Dispute resolution procedure

Red Flags to Watch Out For

• Requests for large cash payments upfront
• Pressure to make quick decisions
• Unwillingness to provide a written quote or contract
• No public liability insurance
• Unable to provide references or examples of previous work
• No landline or business address — only a mobile number
• Recommending you pull permits in your own name (to avoid building control)

Questions to Ask Your Builder

1. Who will actually be on site every day — you or a subcontracted team?
2. Who is your named site manager for this project?
3. How do you handle unforeseen problems (e.g. rotten timbers, drainage issues)?
4. What is your process for managing building regulations inspections?
5. Can I speak to your last three clients?