House Extensions & Loft Conversions in Kensington & Chelsea

LCCL Construction is a design and build company based in Finchley N3, working in Kensington & Chelsea 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.

Kensington and Chelsea is almost entirely conservation area: stucco terraces, mews houses and mansion flats. Basements, full renovations and roof-level extensions are the projects that add space here; every one needs sensitive detailing and careful neighbour management.

What it costs in Kensington & Chelsea

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 Kensington & Chelsea

Weech Road, Hampstead NW6 — penthouse duplex loft conversion

A top-floor flat turned into a penthouse duplex: the kitchen and living space moved up into the new loft, two new bathrooms, an extra bedroom and views across to the Shard, the London Eye and Parliament. LABC Building Excellence Awards 2026 London Regional Winner — Best Conversion or Alteration to an Existing Home.

See the project

Planning in Kensington & Chelsea

RBKC has strict basement policy (single storey, 50% of the garden, construction traffic plans), Article 4 directions and a large listed stock. Pre-application advice and a heritage statement are standard; party wall awards are always required.

Conservation areas and Article 4 directions in Kensington and Chelsea

Nearly three quarters of the borough is protected by 38 conservation areas — Kensington Square, De Vere and Queen’s Gate around W8 and SW7, Chelsea, Royal Hospital, Cheyne and Hans Town across SW3 and SW10, and Ladbroke, Norland, Pembridge and Kensington Park in W10 and W11 — and listed buildings are common. RBKC has made more than 200 street-specific Article 4 directions since 1969 (most between 1976 and 2012) covering streets such as Kensington Square, Carlyle Square, Drayton Gardens and Earls Court Square: they remove permitted development for replacement windows and doors, front boundary walls, roof coverings and other front-elevation alterations, so a planning application is the norm even for modest work. The council has an appraisal for each of its 38 conservation areas, and Listed Building Consent runs alongside planning on the many Grade II houses. Our architects prepare a heritage statement and pre-application submission as standard here.

Basements in Kensington & Chelsea

Every basement in the borough needs full planning permission: the borough-wide Article 4 direction made on 15 April 2015 came into force on 28 April 2016. Local Plan 2024 policy CD11 (the plan was adopted on 24 July 2024) limits a basement to a maximum of 50% of each garden or open part of the site, no more than one storey, at least 1 m of soil above any part of the basement beneath a garden, and no excavation underneath a listed building, and every scheme needs a Construction Traffic Management Plan. The council’s Basements SPD (adopted 14 April 2016) remains the detailed guidance. Roof alterations are decided under policy CD12 and extensions under CD13.

Fees and timescales

A householder application costs £548 (from April 2026, plus the Planning Portal charge) with an eight-week decision period. RBKC’s planning advice service (from 1 April 2026) charges £559 for a householder level 1 (two weeks) or level 2 (four weeks) response and £680 for level 3 after a meeting; with subterranean works the fees are £722, £1,089 and £1,210. Level 1 is not available for listed buildings, and the council’s Fast Track service is suspended until autumn 2026. RBKC sets no numerical daylight rule; we design to the 45-degree line as standard. Party wall notices run alongside planning: two months’ notice for works to a shared wall, one month for excavations within 3 m or 6 m of a neighbour’s foundations.

Building control

The Royal Borough of Kensington and Chelsea runs its own building control service and runs the LABC Partner Authority scheme. We use the council inspector on every project. 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 hand you the completion certificate at the end of the job.

Anderson's advice: start the party wall process early

Most clients underestimate the party wall timeline — it can add three months to a semi-detached or terraced project. We raise it at the first meeting so notices go out while the design is still being finalised, not after.

What our clients say

“The Lccl construction team built my extension with a quick and clean service, they worked non stop through the winter weather.. I would highly recommend this company!”

— Chris Dunn, Google Reviews

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

Kensington & Chelsea is part of our Central London guide. Nearby areas: Camden, Islington, Notting Hill.

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.