House Extensions & Loft Conversions in Hampstead

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

Hampstead is home to our LABC 2026 award winner: the Weech Road NW6 penthouse duplex loft. Villas, mansion flats and top-floor conversions with roof space dominate; extensions are rear and basement-led because plots are valuable and constrained.

What it costs in Hampstead

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).

Recent LCCL projects near Hampstead

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

Also nearby: Fitzjohns Avenue, Hampstead NW3 (velux loft, 2025) · Boundary Road NW8 (basement, renovation, 2023).

Planning in Hampstead

Camden's Hampstead, Belsize and Fitzjohns/Netherhall conservation areas cover most of the area; roof extensions and dormers need planning permission and Camden's design guidance is detailed. Flats also need freeholder consent — we run both in parallel.

Permitted development in Hampstead: what goes ahead without a planning application

Mostly a planning application. Camden’s Article 4 direction has covered Hampstead, Belsize, Fitzjohns/Netherhall and Swiss Cottage since 2010 (amended June 2026), and every basement in the borough needs permission; inside those areas most extensions go through a householder application, which we handle. On streets outside the directions, lofts and single-storey rear extensions go ahead without one. Flats and maisonettes have no permitted development rights, whatever the street, and inside any conservation area a dormer or roof enlargement needs a planning application even where a single-storey rear extension within the limits does not.

On a house outside those streets, a rear dormer loft (40 m³ on a terrace, 50 m³ on a semi or detached house), a hip-to-gable, a single-storey rear extension of 3 m (4 m on a detached house) and a side-return infill are permitted development, and we apply for a Lawful Development Certificate on every one so the position is confirmed in writing. See our fixed-price permitted development projects — from £32,400 inc. VAT (£27,000 + VAT) for a Velux loft and £42,000 inc. VAT (£35,000 + VAT) for a 3 m rear extension, design and build inclusive, postcode dependent. Not sure whether your project needs a planning application?

Planning check

Conservation areas and Article 4 directions in Hampstead

Four Camden conservation areas cover almost all of NW3: Hampstead (designated 1968) around the village, Heath Street and Church Row; Belsize with its mid-19th-century Italianate stucco villas; Fitzjohns/Netherhall (appraisal December 2022), the Queen Anne Revival and Arts and Crafts red-brick houses between Fitzjohn’s Avenue and Finchley Road; and Swiss Cottage/South Hampstead (1988), the large late-Victorian semis and terraces with long rear gardens on the NW6 side. All four have Article 4(1) directions made on 1 September 2010 and amended in June 2026 (the amendment carves out solar panels): on any elevation facing a road, planning permission is needed for replacement windows and doors, walls, porches, decorative features, roofs and rooflights, chimneys, front gardens and boundaries. The directions apply to flats as well as houses, and Camden charges no fee for an application that is only needed because of them. Rear extensions and rear dormers are decided under the Home Improvements guidance below.

The rules Camden applies

Camden’s Home Improvements planning guidance (CPG, adopted 15 January 2021) is qualitative rather than numerical: rear extensions must be subordinate to the house and leave a reasonably sized garden (para 2.1.1), side extensions should be single storey (2.1.2) and roof extensions and dormers must stay subordinate to the roof slope (2.2). The same guidance requires the 45-degree and 25-degree daylight tests from the BRE guide, or a full BRE daylight assessment, so we run the 45-degree check on every Camden design before it goes in.

Basements are the borough’s strictest area. A borough-wide Article 4 direction (made 13 September 2016, in force 1 June 2017) means every basement excavation needs planning permission. Local Plan policy A5 and the Basements CPG limit a basement to one storey, no more than 50% of each garden, less than 1.5 times the footprint of the house and no further than 50% of the house’s depth beyond the rear wall, set back from the boundaries. Every application needs a Basement Impact Assessment prepared by a chartered engineer or geologist and independently audited at the applicant’s cost.

Fees and timescales

A householder application costs £548 (from April 2026, plus the Planning Portal service charge) with an eight-week decision period. Camden’s homeowner pre-application service is £481.50 (level 1) or £963 (level 2) including VAT, and the council adds a £46 administration fee to applications sent by email. 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

Camden runs its own building control service and aims to decide full-plans applications within six weeks. 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: put the rooflights over the island

Rooflights over kitchen islands transform natural light more than any other single design decision. We position them on the plan before the kitchen layout is fixed, not after.

What our clients say

“LCCL Constructions was professional, trustworthy and worked to the highest standard. The process was smooth and I'm very happy with the result - it has transformed the quality of my home.”

— 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

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