House Extensions & Loft Conversions in Barnet

LCCL Construction is a design and build company based in Finchley N3, working in Barnet 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.

Barnet's 1930s semis and post-war detached houses — High Barnet, New Barnet, East Barnet, Whetstone, Totteridge — have hipped roofs and decent plots: hip-to-gable lofts and rear or wraparound extensions are the standard projects. Our Bohun Grove EN4 renovation is ten minutes from the office.

What it costs in Barnet

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 Barnet

Bohun Grove, East Barnet EN4 — hip-to-gable loft, rear extension and whole-house renovation

A total renovation: hip-to-gable loft conversion, rear extension with an open-plan kitchen, two Lusso Stone bathrooms, enlarged bedrooms, new windows, skylights and floor-to-ceiling glazing, a regulated outbuilding and landscaping.

See the project

Planning in Barnet

Barnet is generally straightforward for permitted-development lofts and single-storey rear extensions; conservation areas in Monken Hadley, Totteridge and Wood Street need planning permission for roof changes. We apply for a Lawful Development Certificate on every PD project.

Conservation areas and Article 4 directions in Barnet, Whetstone and Totteridge

Three conservation areas sit inside the EN4, EN5 and N20 postcodes and each has an Article 4 direction that removes some permitted development rights. Monken Hadley (designated 1968, Article 4 from 1972 with a second direction in 2007) covers the Georgian houses and Victorian cottages around Hadley Green and the Common — where a house fronts the road or open space, planning permission is needed for extensions, porches, roof changes, windows, doors, fences and hardstandings. Totteridge (Article 4 from 1972, updated 2008) is the long linear village of mansion houses and cottages along Totteridge Lane and Totteridge Village, where doors, windows, roofing materials, hardstandings, porches and external painting are controlled in parts of the area. Wood Street in High Barnet is the third, listed with a 1972 direction. Elsewhere in East Barnet, New Barnet, Whetstone, Oakleigh Park and Cockfosters the standard permitted development rules apply and most lofts and single-storey rear extensions proceed on a Lawful Development Certificate. A borough-wide Article 4 direction has also removed permitted development for converting a house into a small HMO since 29 May 2016. Our LABC award-winning Bohun Grove EN4 project (extension, loft conversion, full renovation and landscaping) sits outside any conservation area and was approved through a householder planning application to 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: talk to your neighbours before the notices go out

Semi-detached hip-to-gable plus rear dormer combinations almost always fall under permitted development, but neighbours often object informally. A conversation over the fence before the party wall notice lands avoids most of it.

What our clients say

“LCCL Construction were professional from start to finish. The team were trustworthy, reliable and delivered work to the highest standard.”

— KashImaging, Trustpilot

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

Barnet is part of our North London guide. Nearby areas: Finchley, 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.