How to Choose a Builder in London: A Practical Checklist for Homeowners

The builder you choose for a London home project has more impact on the outcome than almost any other decision. The right contractor turns an ambitious plan into a successful project. The wrong one costs you money, time, and significant stress. This checklist covers everything you should verify before committing.

Step 1: Establish What You Actually Need

Before approaching any contractor, be clear on the scope. At minimum, know:

• What type of project it is (extension, loft conversion, refurbishment, structural alteration)
• Whether you have architectural drawings (and if so, what stage they are at)
• Your target start date and budget range
• Whether planning permission has been obtained

Contractors quote more accurately — and take your project more seriously — when you can provide clear information rather than asking for a price based on a verbal description.

Step 2: Source Candidates Responsibly

Good sources:

• Direct recommendation from friends, family, or neighbours who have used the contractor recently for a similar project
• Architect referral (your architect knows which contractors in London actually deliver their designs)
• Trade association directories: FMB (Federation of Master Builders), TrustMark, Checkatrade, TrustATrader, Association of Master Tradesmen
• Local Facebook groups and community platforms (Nextdoor) — read critically, but genuine local recommendations from people you can follow up with are useful

Treat with caution:

• Unsolicited callers or door knockers
• Contractors who appear suddenly with a very cheap price for "work in the area"
• Online directories without independently verified reviews

Step 3: Verify Insurance

Before any contractor visits your site, confirm they hold:

• Public Liability Insurance: Minimum £2 million (most London contractors carry £5 million). This covers damage to your property or injuries to third parties caused by their work.
• Employer's Liability Insurance: Required by law if they employ any staff (even casual labour). Minimum £5 million.
• Professional Indemnity Insurance: If they are also providing design or professional advice as part of the service.

Ask for a copy of the certificate. Call the insurer to confirm it is current if there is any doubt.

Step 4: Check Trade Memberships and Accreditations

Trade memberships do not guarantee quality, but they do indicate that a contractor has submitted to some level of external assessment:

• FMB (Federation of Master Builders): Members are vetted on quality, financial standing, and customer service. Independent dispute resolution available.
• TrustMark: Government-endorsed quality scheme. Requires third-party inspection.
• Checkatrade / TrustATrader: Checked reviews and verified credentials. Read reviews critically — look at volume, recency, and the detail of reviews, not just the star rating.
• NICEIC / NAPIT: For electrical contractors. Confirms Part P competence and authorisation to self-certify electrical work.
• Gas Safe Register: For gas engineers. Verify the individual engineer's registration at gassaferegister.co.uk — the company registration is not sufficient.

Step 5: See Completed Work

Ask to visit a completed project similar to yours. A reputable London contractor should be able to arrange this — former clients who are happy with the work will generally agree to a brief visit.

During the visit:

• Look at the quality of visible finishes — plasterwork, paint, tiling, woodwork
• Ask the homeowner how the contractor communicated during the project
• Ask whether the project finished on time and on budget
• Ask whether they would use the contractor again

Step 6: Evaluate the Quotation

A quotation should be:

• In writing
• Itemised (not a single lump sum)
• Clear about what is included and what is excluded
• Explicit about the basis of the price (fixed price, or cost-plus/provisional sums)
• Clear about material responsibilities (what the contractor supplies vs what the client supplies)
• Accompanied by a proposed programme

Red flags in quotations:

• A single total price with no breakdown
• No mention of exclusions or assumptions
• Materials described vaguely as "as required"
• No mention of Building Regulations, structural engineer, or other professionals
• An unusually low price with no explanation

Step 7: Assess Communication

The quality of a contractor's communication before they start work is usually a good predictor of how they will communicate during the project.

Ask yourself:

• Did they respond promptly to your initial enquiry?
• Did they arrive on time for the site visit?
• Did their quotation arrive when they said it would?
• Do they answer questions clearly and completely?
• Do they seem to understand the project?

Step 8: Understand the Contract

Never start work without a written contract. At minimum, the contract should specify:

• Scope of works
• Start date and completion date
• Payment schedule (stage payments tied to work completion, not arbitrary calendar dates)
• Variation procedure (how changes are agreed and priced)
• Dispute resolution process
• Retention (typically 2.5–5% held back for 6–12 months after completion to cover defects)
• Insurance obligations

Standard contracts for residential works include JCT Homeowner Contracts and plain-English alternatives. Avoid contractors who refuse to sign a contract or want to work from a simple letter or verbal agreement only.

Step 9: Check for References and Previous Disputes

Before signing, ask for references from three recent comparable projects. Call them. Ask specifically about:

• Programme adherence
• Budget adherence
• Communication quality
• How disputes or problems were handled
• Whether they would recommend the contractor without reservation

RCB Design & Build

RCB holds FMB, TrustMark, Checkatrade, and TrustATrader memberships, carries full insurance, and operates under written contracts for every project. We welcome reference requests and site visits to completed projects. Contact us to discuss your project.