House Extensions & Loft Conversions in St John's Wood

LCCL Construction is a design and build company based in Finchley N3, working in St John's Wood 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.

St John's Wood is stucco villas, mansion blocks and mews houses. Basements, full renovations and roof extensions to top-floor flats are the usual projects; the standard of finish expected is high and access is tight.

What it costs in St John's Wood

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 St John's Wood

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 St John's Wood

Westminster's St John's Wood conservation area and listed villas mean planning permission and often heritage statements; basements need Westminster's construction management plan. Freeholder and management-company consents are part of every job.

Conservation areas and Article 4 directions in St John’s Wood

Westminster’s St John’s Wood conservation area was first designated in 1967 and its boundaries were altered in 1979 and 2007; the council’s conservation area audit, adopted as an SPD on 16 June 2008, describes “a mixture of early-mid Victorian detached and semi-detached villas and terraces” unified by yellow stock brick and stucco. The NW8 streets north of the Wellington Road/Finchley Road line fall in Camden, whose separate St John’s Wood conservation area has its own appraisal (June 2009). St John’s Wood has no householder Article 4 direction beyond Abbey Gardens (1969), so front-facing replacement windows remain permitted development — but the audit is clear that “roof extensions are unlikely to be acceptable in St John’s Wood” (para 4.78) and that extensions to the Category 1 listed and unaltered groups “would not normally be acceptable” (4.81), with roof extensions considered only on Category 2 buildings (4.82). Westminster’s design guidance for conservation areas expects rear extensions to stop at the penultimate storey or lower, a significant area of garden to be retained, and regards traditional mansards as most appropriate on 18th- and 19th-century terraces.

Basements

Every basement in Westminster needs planning permission under the city-wide Article 4 direction in force since 31 July 2016, and on the Camden side under Camden’s direction in force since 1 June 2017. Westminster’s basement policy, adopted in 2016 and carried into the City Plan as policy 45, allows no more than one storey below the lowest original floor, no more than 50% of the site curtilage (with an exception for sites under 8 m wide), at least 1 m of soil plus a 200 mm drainage layer over the basement, no unbalancing of a listed building’s hierarchy of spaces, a detailed structural methodology statement self-certified by a suitably qualified engineer and a construction management plan under the Code of Construction Practice. Camden requires an independently audited Basement Impact Assessment.

Fees and timescales

The City Plan 2019–2040 was adopted in April 2021 and its partial review in January 2026. A householder application costs £548 (from April 2026, plus the Planning Portal charge) with an eight-week decision period. Westminster’s pre-application service (2025/26 schedule) charges £456 including VAT for a written householder response in 28 days, £912 with a meeting for a householder basement, and £2,016 for a listed householder scheme. Westminster sets no numerical daylight rule for householder schemes; 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

Westminster runs its own building control service. 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

“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

St John's Wood is part of our North West London guide. Nearby areas: Mill Hill, Hampstead, Queen's Park.

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.