How to Choose a Building Contractor: The Right Questions, Red Flags, and Process

**Match contractor scale to project scale**:

• Before comparing prices, verify you are comparing contractors appropriate for your project type and size:
• •*Small works* (£2,000–£15,000): bathroom refurbishment, single room decoration, kitchen replacement — appropriate for specialist sole traders or small specialist contractors
• •*Medium projects* (£15,000–£60,000): loft conversion, single-storey extension, flat refurbishment — appropriate for established residential contractors with a stable site team
• •*Larger projects* (£60,000+): double-storey extension, whole-house refurbishment, structural alteration with loft — need project management capability, long-term relationships with structural engineers and Building Control, and an employed or reliably subcontracted workforce

A sole trader experienced in small bathroom works is not the right contractor for a £75,000 loft conversion. A regional contractor used to commercial fit-outs may be uncompetitive or inappropriate for a domestic kitchen extension.

**Where to find contractors**:

• •*Checkatrade, TrustATrader, Which? Trusted Traders*: Platform membership requires vetting; reviews are verified as genuine; you can filter by trade, location, and project type. Review score and review volume both matter — a 9.8/10 with 200 reviews is much more informative than a 10/10 with 3 reviews.
• •*Federation of Master Builders (FMB)*: Members are vetted on insurance, references, and financial standing; ongoing disciplinary process; complaint escalation available. Verify any claimed FMB membership at fmb.org.uk/find-a-builder.
• •*TrustMark*: Government-endorsed quality scheme for home improvement; independent of individual trade bodies. Verify at trustmark.org.uk.
• •*Personal recommendation*: The most reliable source — ask neighbours, friends, or colleagues who have recently had similar work done. A recommendation based on an actual recent project outcome is worth far more than any platform profile.
• •*Architect or structural engineer recommendation*: Where you are working with a professional, their contractor recommendation is typically based on prior working experience and delivery performance — very valuable.

**Insurance — what to verify before getting quotes**:

• •*Public liability insurance*: Minimum £1m for small works; £2m+ for medium-large projects. Ask for a copy of the certificate — not verbal confirmation. Check the policy is current and the limit is adequate.
• •*Employer's liability insurance*: Required by law for any contractor who employs anyone. Ask for a certificate.
• •*Contractor all-risk (works insurance)*: Covers the works in progress against damage or loss. For larger projects, ask whether this is in place — otherwise notify your own buildings insurer that works are ongoing.

**Verifying accreditations**:

• •FMB: fmb.org.uk/find-a-builder
• •Checkatrade profile: check the date of the most recent review, the volume of reviews, and any recurring themes in negative reviews
• •Gas Safe: gassaferegister.co.uk — mandatory for any gas work
• •NICEIC or NAPIT: niceic.com or napit.org.uk — for electrical work
• •MCS: mcscertified.com — for solar PV or heat pump installations

These checks take 5–10 minutes and filter out a significant proportion of contractors who should not be trusted with a domestic project.

**Questions to ask at tender stage (before quotes are returned)**:

• *About the team*:
• •Who will be the site manager or foreman on my project? Will I meet them before I sign?
• •Will the works be done by your own employed team, or subcontracted?
• •How many other projects will be running simultaneously with mine?

• *About the quote*:
• •What are the main provisional sums and assumptions in your quote?
• •Under what circumstances would I face additional costs?
• •Who appoints the structural engineer — you or me? Are their fees included?
• •Who makes the Building Regulations application? Are those fees included?

• *About programme*:
• •What is your proposed start date and completion date?
• •How many other projects are you committed to starting within 6 weeks of mine?

• *About variations*:
• •How do you handle changes to scope during the project?
• •Do you issue written variation notices before carrying out additional work?

• *About completion and defects*:
• •What is your defects liability period after practical completion?
• •How do you manage snagging?

**Taking up references properly**:

A reference provided by the contractor is only valuable if you follow it up by direct contact with the client — not by reading a written testimonial the contractor has supplied.

• *What to ask references*:
• •Was the final account within 10–15% of the original quote? Were there many unexpected additional costs?
• •Was the programme met? If not, how much did it overrun and why?
• •How was the site managed — was there consistent supervision and a clean, orderly site?
• •How were variations handled — were they agreed in writing before work was done?
• •Were defects at practical completion dealt with promptly?
• •Would you use this contractor again?
• •Is there anything you wish you had known before appointing them?

*Reference selection*: Ask for 2–3 references specifically for projects similar in type and scale to yours (not a kitchen refurbishment when yours is a loft conversion), completed within the last 1–2 years.

**Visiting a live site**:

• Where possible, ask to visit the contractor's current project. A site visit reveals:
• •Whether the site is clean, well-organised, and properly managed
• •Whether materials are stored correctly and safely
• •Whether PPE and site safety standards are observed
• •Whether the team appears competent and directed

**Always use a written contract**:

• For all but the smallest domestic works, use a recognised written form:
• •*JCT Minor Works Building Contract (MW)*: Appropriate for projects with good drawings and specification, fixed scope, and a client-appointed architect or contract administrator. Includes a formal variation mechanism and adjudication for disputes.
• •*FMB Building Contract*: Specifically designed for domestic projects; plain English; consumer protection provisions included. Widely used for domestic extensions and refurbishments.
• •*HomeOwner's Contract (NBS)*: Also suitable for domestic projects without a solicitor.

At minimum, even for smaller works: a detailed written quotation specifying scope, price, payment schedule, programme, and dispute process gives meaningful protection even without a formal standard form. An oral agreement is not sufficient.

**Payment terms — what is reasonable**:

• •*Mobilisation deposit*: 5–10% of contract value before start (to cover initial materials and site set-up)
• •*Stage payments*: Aligned to visible physical progress milestones — not to calendar dates or the contractor's cash flow needs
• •*Retention*: 2.5–5% of contract value withheld until practical completion + defects liability period (typically 3–6 months)

*What to avoid*: Requests for 30–50% upfront before starting; cash payments with no VAT receipt; stage payments that significantly exceed the value of work done at that stage.

**Red flags — when to walk away**:

• •No public liability insurance or expired certificate
• •No verifiable trade body membership or accreditation
• •Request for more than 10–15% upfront payment
• •Pressure to sign immediately and start next week
• •Resistance to a written contract
• •Inability to provide references for recent comparable projects
• •No fixed price — 'we'll bill you as we go'
• •Significantly lower than all other quotes with no detailed explanation
• •No mention of Building Regulations application for works that clearly require it
• •Quote based on a brief phone call — no site visit