Home Extension Builders London: 7 Things to Check Before You Appoint
Updated: Nov 2
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.
Not sure whether your project needs planning permission? Enter your postcode and tick what you want to build — we look up the conservation areas, Article 4 directions and listed buildings for you, and you see which parts are permitted development and the from-price for each. Lawful Development Certificate included on every permitted development job.
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 designs and builds 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 £42,000 inc. VAT (£35,000 + VAT). Side return extension: from £42,000 inc. VAT (£35,000 + VAT). Kitchen extension: from £48,000 inc. VAT (£40,000 + VAT). Wraparound extension: from £72,000 inc. VAT (£60,000 + VAT). Double storey extension: from £96,000 inc. VAT (£80,000 + VAT). See our full house extension cost guide for a complete breakdown.
Can it be done under permitted development?
A single-storey rear extension of 3 m on a terrace or semi (4 m on a detached house), a side-return infill and a side extension up to half the original width are permitted development on a house outside a conservation area or Article 4 street — no planning application, just a Lawful Development Certificate, which we apply for on every one. Fixed-price permitted development extensions start from £42,000 inc. VAT (£35,000 + VAT) at economy specification, design and build inclusive, and the 6 m / 8 m larger home extension goes through a 42-day prior approval notification rather than a full application. See our permitted development projects page for every product with its from-price and the checks we run before we confirm a project qualifies.
Not sure whether your project needs planning permission? Enter your postcode and tick what you want to build — we look up the conservation areas, Article 4 directions and listed buildings for you, and you see which parts are permitted development and the from-price for each. Lawful Development Certificate included on every permitted development job.
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 £35,000 to £75,000 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.
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