Home Extension Builders London: 7 Things to Check Before You Appoint

Finding the right home extension builders in London is one of the most important decisions you will make when planning a house extension. With so many builders operating across London, knowing what separates a reliable specialist from the rest is essential. Here are 7 things every homeowner should check before appointing home extension builders in London.

LCCL Construction — specialist home extension builders based in Finchley, North London

7 Things to Check When Choosing Home Extension Builders in London

1. A Proven Track Record of Completed Extensions

Ask to see photos of recently completed extension projects similar to yours. Any professional home extension builder should have a portfolio of finished projects they are proud to show. Be specific — if you want a rear extension, ask to see completed rear extensions. If you want a wraparound extension, ask to see completed wraparound projects. LCCL Construction has completed hundreds of extensions across London and Hertfordshire and our portfolio is available at lcclconstruction.co.uk/portfolio.

2. 50+ Verified Reviews at 4.5 Stars or Above

Verified reviews across independent platforms are the most reliable indicator of consistent quality. Look for home extension builders with a minimum of 50 reviews at 4.5 stars or above across Google, Houzz, Trustpilot and Reviews.io. A sudden surge of five-star reviews should raise questions. LCCL Construction has over 200 verified reviews at 4.7 out of 5 built over 20 years.

3. LABC Registered Partner or NFB Membership

LABC Registered Partner status and National Federation of Builders membership are the most relevant professional accreditations for home extension builders in London. Both involve independent vetting of quality and professional standards. LABC Registered Partners can offer a 10-year structural warranty on completed projects. LCCL Construction holds both LABC Registered Partner status and NFB membership and won the LABC Award 2024 for Best Residential Extension.

4. A Full Design and Build Service

The most efficient approach to building a home extension is through a design and build company that handles architectural design, planning permission, building regulations, structural calculations, party wall agreements and construction under one roof. This eliminates the communication gaps and cost uncertainty that arise when you use separate architects and builders.

5. A Detailed Written Estimate

Always insist on a detailed written estimate that covers every element of the project — foundations, structure, roof, glazing, electrics, plumbing, plastering and decoration. Verbal quotes and vague one-line estimates are a common source of disputes and budget overruns. Ask builders to specify exactly what is and is not included so you can make a genuine like-for-like comparison.

6. Responsive Communication Before You Appoint

Test a builder's responsiveness during the quotation stage. If they are slow to reply to messages or miss consultation appointments before you have appointed them, this behaviour will be significantly worse once they have your deposit. Good home extension builders respond promptly, keep appointments and communicate clearly throughout the project.

7. A Dedicated Project Manager on Your Build

Every LCCL Construction home extension has a dedicated project manager who is your single point of contact from start to completion. They coordinate all trades, manage the build programme, liaise with building control and keep you updated weekly. A dedicated project manager is the difference between a build that runs smoothly and one that stalls.

How Much Do Home Extensions Cost in London in 2026?

Rear extension: from £35,000. Side return extension: from £35,000. Kitchen extension: from £40,000. Wraparound extension: from £60,000. Double storey extension: from £80,000. See our full house extension cost guide for a complete breakdown.

Frequently Asked Questions About Home Extension Builders in London

How do I find reliable home extension builders in London?

Look for builders with 50+ verified reviews at 4.5 stars or above, LABC Registered Partner or NFB membership, a full design and build service and a detailed written estimate. LCCL Construction meets all of these criteria.

How much do home extension builders charge in London?

Home extension builders in London typically charge £35,000 to £80,000 for a single storey extension and £80,000 to £150,000 for a double storey extension for a full design and build service.

To get a free consultation and detailed estimate from LCCL Construction, call 020 8037 7332 or get an instant quote online.