How much should I pay as a deposit to a London builder?

Industry standard: 0–10% of contract value. Many reputable contractors take no deposit at all and bill against work completed. Anything above 10% is a red flag — the builder may be cash-strapped and using your deposit to fund other projects. Never pay 50% upfront or anything close to it.

Should I get multiple quotes before choosing a builder?

Yes — get 2–3 quotes minimum. Compare not just price but scope, specification, programme and contract terms. The lowest quote often turns out to be the most expensive because of missing scope or provisional sums. The middle quote is usually most reliable. Cheapest is rarely best on a £80,000+ project.

What is a JCT contract and why does it matter?

JCT (Joint Contracts Tribunal) is the industry-standard suite of construction contracts. JCT Minor Works covers projects under £250,000 — typical loft conversions and extensions. The contract defines scope, price, programme, payment, variations, insurance, defects period and dispute resolution. It protects both parties. A reluctance to use a JCT contract — or any formal written contract — is a major red flag.

How long should a London builder's warranty be?

Standard: 12 months from practical completion (defects liability period). After that, statutory rights under the Defective Premises Act 1972 give 6 years for major defects. For new builds and extensions, NHBC or LABC structural warranties provide 10 years of cover. Builderr provides a full 12-month defects period plus 10-year structural warranty on extensions and loft conversions.

How to Find a Reliable Builder in London 2025 — Full Guide

How Do I Find a Reliable Builder in London?

To find a reliable London builder: check FMB, TrustMark or NHBC accreditation; verify public liability insurance (£2m minimum) and contractors' all risks insurance; ask for 3 references from completed projects in the last 12 months; visit a current site; insist on a written fixed-price contract (JCT Minor Works or equivalent); avoid cash-only quotes, deposits over 10% and verbal-only agreements. Get at least 2–3 quotes for comparison.

Accreditation: what to look for

Reliable London builders typically hold accreditation from one or more of: Federation of Master Builders (FMB) — vetted membership, third-party complaints scheme; TrustMark — government-endorsed quality scheme; NHBC or LABC Warranty — new-build and extension warranty providers, only available to vetted contractors; Construction Industry Training Board (CITB) — apprenticeship and skill standards. Specific trade accreditations: NICEIC, NAPIT or ELECSA for electricians (building regs Part P); Gas Safe Register for gas engineers; SafeContractor or CHAS for health and safety; ConstructionLine for procurement standards. Check the contractor's company on Companies House for company age, accounts and director history — newly formed companies with directors who have failed previous companies are a red flag.

Insurance: what to verify

Every London builder you engage should hold three types of insurance. Public Liability Insurance (£2m minimum, £5m preferable for substantial projects) — covers damage to neighbours and third parties. Employer's Liability Insurance (£10m minimum, legally required if they have employees) — covers injury to workers. Contractors' All Risks (CAR) Insurance — covers the works themselves during construction, including materials on site, theft and damage. Ask for current certificate of insurance from each insurer; check the dates are current; verify the cover sum matches your project value. Don't engage a contractor whose insurance is expired or inadequate — your home insurer may refuse to cover claims arising during the works.

References and site visits

Ask for at least 3 references from completed projects in the last 12 months — recent enough that the work hasn't aged, similar enough in scope to your project. Speak to each reference by phone or in person: ask about quality, timeliness, communication, change orders, how problems were handled, whether they would use the builder again. Visit at least one current site — a contractor who refuses site visits is hiding something. On site, observe: cleanliness, safety (scaffolding, signage, PPE), the trades on site (skilled? professional?), the foreman or site manager's communication, how materials and waste are managed. A well-run site looks orderly even mid-build.

Contracts and red flags

Insist on a written fixed-price contract — JCT Minor Works (under £250,000), JCT Intermediate (£250,000–£1m) or JCT Standard (above £1m) are the industry standards. The contract should specify: scope of work in detail (drawings, specifications); fixed price (with separate sums for any provisional items); programme dates; payment schedule (typically valued monthly against work done, with retention); change order process; insurance requirements; warranty period (12 months minimum). Red flags: deposits over 10% of contract value (the industry standard is 0–5%); cash-only payment; verbal-only quotes with no written breakdown; pressure to sign immediately or 'special prices today'; quotes significantly below other quotes (likely missing scope); reluctance to provide insurance certificates or references.