Extension Builders Near Me London: 6 Things to Check Before You Appoint

When searching for extension builders near you in London, the quality and reliability of the company you choose matters far more than proximity. London has hundreds of builders offering extension services but standards vary enormously. The best extension builders combine local knowledge, professional accreditations, a proven track record and a full design and build service. LCCL Construction is based in Finchley, North London and delivers house extensions across all of London and Hertfordshire.

LCCL Construction — specialist extension builders across London and Hertfordshire

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.

Planning check

6 Things to Check When Looking for Extension Builders Near You in London

1. Verified Reviews Across Multiple Platforms

Before appointing any extension builder, check their reviews across Google, Houzz, Trustpilot and Reviews.io. Look for a minimum of 50 verified reviews at 4.5 stars or above. A builder with 200+ reviews built over 20 years is a far stronger signal of consistent quality than one with 20 recent reviews. LCCL Construction has over 200 verified reviews at 4.7 out of 5 built over 20 years of delivering extensions across London.

2. LABC Registered Partner or NFB Membership

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

3. A Full Design and Build Service

The most efficient way to build a house 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. One company, one estimate, one point of contact.

4. Experience With Your Specific Extension Type

Ask specifically about recent completed projects of your extension type — rear extension, side return, wraparound or double storey. LCCL Construction designs and builds all extension types across London and Hertfordshire.

5. A Detailed Written Estimate

Never accept a verbal quote or a vague one-line estimate. A professional extension builder provides a detailed written estimate covering foundations, structure, roof, glazing, electrics, plumbing, plastering and decoration. Hidden exclusions are the most common source of budget overruns. LCCL Construction provides a detailed written estimate before any work begins with no hidden costs.

6. A Dedicated Project Manager

Poor communication is the most common complaint about builders. Test responsiveness during the quotation stage. LCCL Construction assigns a dedicated project manager to every extension who provides weekly updates, coordinates all trades and manages the build from start to completion.

How Much Do House Extensions Cost in London in 2026?

Rear extension: from £42,000 inc. VAT (£35,000 + VAT).

Side return: from £42,000 inc. VAT (£35,000 + VAT).

Kitchen extension: from £48,000 inc. VAT (£40,000 + VAT).

Wraparound: from £72,000 inc. VAT (£60,000 + VAT).

Double storey: from £96,000 inc. VAT (£80,000 + VAT).

See our full house extension cost guide.

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.

Planning check

Frequently Asked Questions About Extension Builders Near Me in London

How do I find reliable extension builders near me in London?

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

To get a free consultation call LCCL Construction on 020 8037 7332 or get an instant quote online.