House Extensions & Loft Conversions in Finchley

LCCL Construction is a design and build company based in Finchley N3, working in Finchley for over 20 years. One team, one contract: architects, structural engineers, project managers and builders coordinated by LCCL take your project from first sketch to handover.

Finchley N3 is where LCCL is based. The Edwardian and 1930s houses of Church End, East Finchley and North Finchley suit rear dormers, hip-to-gable lofts and kitchen extensions; the tighter terraces around Long Lane and Squires Lane take side-return extensions well.

What it costs in Finchley

The final figure depends on postcode, access and site conditions — the instant estimate applies your area. Guide ranges for 2026, design and build inclusive (architecture, structural engineering, planning or LDC, construction, project management and building control). Every project is surveyed and priced individually.

• Velux loft: £32,400 – £50,400 inc. VAT (£27,000 – £42,000 + VAT)
• Rear dormer loft: £56,400 – £80,400 inc. VAT (£47,000 – £67,000 + VAT)
• L-shaped dormer: £58,800 – £98,400 inc. VAT (£49,000 – £82,000 + VAT)
• Hip to gable: £60,000 – £114,000 inc. VAT (£50,000 – £95,000 + VAT)
• Mansard: £76,800 – £148,800 inc. VAT (£64,000 – £124,000 + VAT)
• Rear extension: £42,000 – £90,000 inc. VAT (£35,000 – £75,000 + VAT)
• Side return: £42,000 – £93,600 inc. VAT (£35,000 – £78,000 + VAT)
• Wraparound: £72,000 – £153,600 inc. VAT (£60,000 – £128,000 + VAT)
• Double storey: £90,000 – £198,000 inc. VAT (£75,000 – £165,000 + VAT)

Kitchen on top of the structure, supplied and fitted: +£9,000 – £87,360 inc. VAT (£7,500 – £72,800 + VAT) depending on size and specification. Basements: cellar refit £54,000 – £114,000 inc. VAT (£45,000 – £95,000 + VAT), lowering £114,000 – £216,000 inc. VAT (£95,000 – £180,000 + VAT), new dig £216,000 – £360,000 inc. VAT (£180,000 – £300,000 + VAT)+. New build: £2,200 – £4,500 per sqm (zero-rated for VAT).

A recent LCCL project near Finchley

Guardhouse Way, Millbrook Park, Mill Hill NW7 — kitchen extension

A large modern kitchen and dining space for a family home, with a separate utility room so the kitchen stays quieter and gains cupboard space.

See the project

Planning in Finchley

Barnet council; most lofts and rear extensions proceed under permitted development, with the Finchley Church End and Hampstead Garden Suburb conservation areas the exceptions (Hampstead Garden Suburb has its own Trust approval on top of planning).

Conservation areas and Article 4 directions in Finchley

Finchley has more conservation areas than any other part of the borough, so the first thing we check is the address. Finchley Church End (1979; Article 4 2011) covers the Victorian cottages around Hendon Lane, Gravel Hill and College Terrace — the 2011 direction applies to listed properties fronting the street. Finchley Garden Village (Article 4 since 1979), Glenhill Close (Article 4 2002) and Moss Hall Crescent in North Finchley (Article 4 1987) are small residential areas where front-facing changes, roof alterations and porches need planning permission. College Farm is a conservation area without an Article 4 direction. On the N2 side, Hampstead Garden Suburb is the strictest regime in London: its 1971 Article 4 direction removes permitted development for any extension, roof extension, porch, outbuilding, hardstanding, replacement windows, doors or roofing materials and even external painting, and every scheme also needs Scheme of Management approval from the Hampstead Garden Suburb Trust before Barnet will determine it. Outside these areas — most of N3, N12 and the 1930s streets of West Finchley and Woodside Park — lofts and single-storey rear extensions normally proceed under permitted development with a Lawful Development Certificate from Barnet.

Extension size rules Barnet applies (SPD adopted 15 June 2026)

Barnet adopted its Sustainable Design and Development Guidance SPD on 15 June 2026, replacing the 2016 Residential Design Guidance, and Part 4 of it sets the numbers officers use alongside Local Plan policy CDH05. Single-storey rear extensions can run the full width of the house to a maximum depth of 3 m on a terrace, 3.5 m on a semi and 4 m on a detached house (paras 4.37–4.39), no more than half the garden length (4.40), up to 4 m high with a pitched roof but with eaves no higher than 3 m (4.41–4.42). A larger home extension approved under prior approval (6 m on a semi or terrace, 8 m detached) is accepted as a fallback position (4.45). Two-storey rear extensions are limited to half the width of the house and 3 m deep, kept 2 m from an attached neighbour’s boundary or 1 m from a detached one, with a pitched roof matching the original (4.53–4.57). Side extensions should be no more than half the original width; at first floor they need a 1 m gap to the boundary, a 0.5 m set-back from the front wall and a ridge 0.5 m below the main roof (4.69–4.74). Rear dormers should sit at least 0.5 m in from the eaves, ridge and edges of the roof (4.87); L-shaped dormers over an outrigger are limited to half its depth (4.95); front dormers are generally not supported (4.85), while a hip-to-gable that re-balances a pair of semis is (4.84). Basements are single storey with 2.5 m head height, project no further than the rear-extension limits above, take up no more than half the garden length and have front lightwells of no more than 1 m (4.103–4.121). In the Green Belt the original house should not grow by more than 25% by volume (4.163).

Light to neighbours

The SPD does not set a numerical daylight test; it asks officers to weigh loss of light to main windows of neighbours’ habitable rooms (para 4.7) and to reduce depth or height, or set off the boundary, where levels or building lines differ (4.8). In practice we design every Barnet extension to clear a 45-degree line taken from the centre of the nearest neighbouring habitable-room window, on plan and on elevation — the rule of thumb most London officers use — so the scheme does not need a separate daylight and sunlight report.

Fees, timescales and building control

A householder planning application costs £548 from April 2026 (Planning Portal service charge on top); a Lawful Development Certificate for a proposed use is half that. Barnet has eight weeks from validation to decide a householder application; larger-home-extension prior approval is a 42-day route with a £249 fee. Party wall notices run alongside: two months for works to a shared wall, one month for excavations within 3 m or 6 m of a neighbour’s foundations. We use LABC Barnet on every project, so the inspector is the council’s own. Typical inspection points are commencement, foundation trenches, oversite and damp-proof course, drainage before backfill, structural steels and joists before they are covered, insulation and fire-stopping before plastering, then completion. We book each one and send you the completion certificate at handover.

Anderson's advice: book your start date around the school year

August is our slowest month for project starts — most families delay until schools go back. If you can start in August you often get an earlier slot and a quieter street for scaffolding.

What our clients say

“Super professional and on the ball at all times. All his teams are excellent and hard working. They are conscientious and want the job to be well done.”

— Ludovic, Reviews.io

As LABC Building Excellence Award winners in 2024 (Best Residential Extension in London) and 2026 (Best Conversion or Alteration to an Existing Home, Weech Road NW6), every project is delivered by one team of architects, structural engineers, project managers and builders. Workmanship is guaranteed for 12 months from practical completion, with a 10-year LABC structural warranty.

Nearby areas

Finchley is part of our North London guide. Nearby areas: Barnet, Enfield, Edgware, Hendon, Muswell Hill, Highgate, Crouch End, Stoke Newington.

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

One team, one contract, one point of contact — from first sketch to handover.