Loft conversions, house extensions, renovations, basements and new builds across London and Hertfordshire.
Services
Loft conversions, house extensions, renovations, basements and new builds across London and Hertfordshire.
Services
Loft conversions, house extensions, renovations, basements and new builds across London and Hertfordshire.
Services
Loft conversions, house extensions, renovations, basements and new builds across London and Hertfordshire.
Services
Call 020 8037 7332 or get an instant estimate online.
Loft conversion cost · London & Hertfordshire
Loft conversion cost in London 2026: every type priced, and why they differ
By Anderson & the LCCL Construction Team
Finchley N3 · Design & build, LABC award winners 2024 and 2026
A loft conversion in London costs £32,400 – £148,800 inc. VAT (£27,000 – £124,000 + VAT) in 2026, design and build inclusive — from a Velux conversion in a tall roof to a mansard across the whole footprint. This page gives you the range for each type from the price table we build to, what is in the figure, what moves it, and how to get an itemised estimate for your roof.
Quick answer
£32,400 – £148,800 inc. VAT (£27,000 – £124,000 + VAT) design and build inclusive, depending on the type: Velux from £32,400 inc. VAT (£27,000 + VAT), dormer from £56,400 inc. VAT (£47,000 + VAT), hip-to-gable from £60,000 inc. VAT (£50,000 + VAT), mansard from £76,800 inc. VAT (£64,000 + VAT). Postcode dependent.
Velux, dormer, L-shaped and hip-to-gable conversions within 40 m³ (terrace) or 50 m³ (semi/detached) are usually permitted development; mansards, flats and conservation areas need a planning application.
4–16 weeks on site depending on the type; 8–16 weeks of design and approvals before that.
A free 30-minute phone call with our team, no obligation.
Guide price
£32,400 – £148,800 inc. VAT (£27,000 – £124,000 + VAT)
Typical build
4–16 weeks on site
Guarantee
12-month workmanship guarantee; 10-year LABC structural warranty
Awards
LABC 2024 & 2026 winners
LABC Building Excellence Award 2024
Best Residential Extension in London — Bohun Grove, East Barnet EN4: rear extension, hip-to-gable loft conversion and whole-house renovation
LABC Building Excellence Awards 2026
London Regional Winner, Best Conversion or Alteration — Weech Road, Hampstead NW6: penthouse loft conversion and full renovation
One contract
Architecture, structural engineering, planning, construction and project management — all under one contract
Guaranteed & insured
12-month workmanship guarantee; 10-year LABC structural warranty
How much does a loft conversion cost in London in 2026?
Guide ranges by conversion type, design and build inclusive. Every roof is surveyed and priced individually.
Loft conversion type
What it gives you
Guide range
Velux / rooflight
Roof kept, windows in the slope — lowest-cost, needs a tall roof
£32,400 – £50,400 inc. VAT (£27,000 – £42,000 + VAT)
Box on the rear slope, full-height bedroom and en-suite
£56,400 – £80,400 inc. VAT (£47,000 – £67,000 + VAT)
Rear dormer plus outrigger dormer — two rooms on a terrace
£58,800 – £98,400 inc. VAT (£49,000 – £82,000 + VAT)
Hipped side rebuilt as a gable, usually with a rear dormer — the semi answer
£60,000 – £114,000 inc. VAT (£50,000 – £95,000 + VAT)
New roof across the footprint — most space, usually planning
£76,800 – £148,800 inc. VAT (£64,000 – £124,000 + VAT)
Build time
On site
Planning
Velux / rooflight
4–6 wks
Permitted development
Rear dormer or L-shaped dormer
8–12 wks
Permitted development within 40/50 m³
Hip-to-gable with dormer
10–12 wks
Permitted development within 50 m³
Mansard
12–16 wks
Planning application
Where the money goes
What a design and build loft price is made of, and which lines are priced separately.
Cost element
What it covers
How it is priced
Survey, design and approvals
Measured survey of the roof, drawings, lawful development certificate or planning, building-regulations drawings, structural calculations
Included in the design and build price; council fees at cost
Structure
New floor joists and steels, dormer or gable structure, roof and windows
The largest share — a dormer adds a box structure, a hip-to-gable rebuilds a roof slope, a mansard replaces the roof
Stairs, fire and insulation
New staircase, fire doors, escape windows, insulation to building regulations
Included; the staircase position is the single biggest design decision
First and second fix
Electrics, plumbing, plaster, decoration
Included
Bathroom or en-suite
Where specified
Included to a sanitaryware allowance; items above the allowance are supplied by you or through us
Party wall
Notices to each adjoining owner where the new steels bear on the shared wall
£300 per notice at cost; surveyor from £750 if a neighbour dissents
Location
Access, parking, conservation conditions
Varies by postcode — the instant estimate applies your area
Added afterwards
—
Nothing: the figure on your itemised estimate is the figure you pay
What the price includes: survey, drawings, lawful development certificate or planning, building-regulations drawings, structural calculations, new floor structure, dormer or gable structure, roof and windows, stairs, insulation, fire doors and escape windows, first and second fix, plastering, decoration, a bathroom where specified, LABC certificate and guarantees. Not included unless specified: sanitaryware above the allowance, bespoke joinery, party wall surveyor fees if a neighbour dissents (from £750). The figure on your itemised estimate is the figure you pay — nothing is added afterwards. Postcode dependent — the instant estimator adjusts the range for your area in thirty seconds, and a detailed itemised estimate follows one survey.
Why the types cost what they do: Velux is lowest-cost because the roof structure stays — you pay for floor, stairs, insulation and windows. A dormer adds a box structure and a flat roof. Hip-to-gable rebuilds a whole roof slope, so it costs more but gives the biggest room on a semi. A mansard is a new roof on almost the whole footprint — the most space and the most money, and usually a planning application. Inner and Central London (Camden, Islington, Hackney, Wandsworth, Hammersmith, Westminster, Kensington & Chelsea, the City) cost more than outer London and Hertfordshire a little less — the instant estimate applies your postcode. These are estimated ranges — every home is surveyed and costed individually.
What a loft conversion from LCCL includes
Design and build inclusive — one contract from the first sketch to the completion certificate.
Measured survey of the roof space, stairs and existing structure
Architectural design and drawings, with revisions until you're happy
Lawful Development Certificate or planning application, prepared and submitted for you
Building regulations drawings and structural calculations by our chartered engineer
Party wall notices served on your behalf (£300 each, at cost)
New floor structure, steels, dormer or gable structure, roof and windows
Staircase, insulation, fire doors and escape windows to building regulations
Plaster finish, first-fix electrics and plumbing; bathroom or en-suite where specified
Second-fix carpentry, decoration and the items you supply fitted
LABC inspections and completion certificate
A dedicated project manager and a weekly progress update
12-month workmanship guarantee; 10-year LABC structural warranty
Recent loft conversion projects
Bohun Grove, East Barnet EN4 — rear extension, hip-to-gable loft and whole-house renovation
LABC 2024 Best Residential Extension in London
Semi-detached family home One programme loft + extension + renovation
A total renovation of a family semi: a rear extension opening into a full-width kitchen and dining space with floor-to-ceiling glazing and skylights, a hip-to-gable loft conversion with a rear dormer, two Lusso Stone bathrooms, enlarged bedrooms, new windows throughout, a regulated outbuilding and landscaping.
Because the loft and extension ran under one contract, the steelwork for the open-plan ground floor and the loft floor was designed together and lifted in on the same day — one crane hire, one scaffold, one building-control file.
See the Bohun Grove project · All projects
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ANDERSON · FOUNDER, LCCL CONSTRUCTION
Anderson's advice: talk to next door before the scaffold goes up
Semi-detached hip-to-gable and rear dormer combinations almost always fall under permitted development, but neighbours often object informally — to the council, to the building inspector, to you. Talk to them before the scaffold goes up. We will show them the drawings with you.
It costs nothing, and it is the difference between a quiet twelve weeks and a formal complaint that stalls the job.
“Total refurbishment and side return extension in East Finchley. LCCL totally refurbished our 3-bed Victorian terraced house in East Finchley and built a new 5m side return extension. This means rewiring, re-plumbing, drainage, sewer, and waste. Building a…”
A Davidsson · Google Reviews
“LCCL Construction did the loft design and submission to Barnet Council on our NW4 property. The service from Alexander and his team was outstanding, from beginning to end. Our initial application was rejected, but the designer came up with new drawings –…”
Peter Thompson · Trustpilot
“I highly recommend LCCL Construction. They completed our loft conversion to a very high standard, and the quality of their work throughout was excellent. The team was professional, reliable, and completed everything within a very reasonable timeframe. They…”
Alina A · Trustpilot
Loft conversion cost questions we get asked most
A Velux or rooflight conversion, from £32,400 inc. VAT (£27,000 + VAT) in 2026, because the roof structure stays and you pay for the floor, stairs, insulation and windows. It needs a tall roof — about 2.4 m to the ridge — to give a usable room without a dormer.
£56,400 – £80,400 inc. VAT (£47,000 – £67,000 + VAT) for a rear dormer with a bedroom and en-suite, and £58,800 – £98,400 inc. VAT (£49,000 – £82,000 + VAT) for an L-shaped dormer that adds a second room over the outrigger on a terrace. Both are usually permitted development.
£60,000 – £114,000 inc. VAT (£50,000 – £95,000 + VAT): the hip-to-gable alone from £60,000 inc. VAT (£50,000 + VAT), with a rear dormer £72,000 – £96,000 inc. VAT (£60,000 – £80,000 + VAT), and a double hip-to-gable with dormer on a detached house £90,000 – £114,000 inc. VAT (£75,000 – £95,000 + VAT).
Because it replaces the roof with near-vertical walls and a flat top across almost the whole footprint — £76,800 – £148,800 inc. VAT (£64,000 – £124,000 + VAT) — and it almost always needs a planning application. It gives the most space of any conversion, which is why period terraces in premium postcodes choose it.
Sanitaryware above the allowance, bespoke joinery, council planning fees, and party wall surveyor fees if a neighbour dissents (from £750 per neighbour). Survey, design, approvals, structure, stairs, insulation, fire safety, first and second fix, decoration, LABC sign-off and guarantees are all in the price.
Yes — every figure is postcode dependent. Parking, access, conservation-area conditions, party wall complexity and logistics all move it, so the instant estimator adjusts the range for your postcode and the detailed itemised estimate follows one survey.
No. The figure on your itemised estimate is the figure you pay — nothing is added afterwards. Items you choose, such as kitchen units or sanitaryware above the allowance, are listed separately before you sign.
Two steps. The instant estimator gives you a range for your postcode and project in thirty seconds. Then one measured survey gives you a detailed itemised estimate — design, planning, structure, construction and warranty priced line by line — with no obligation.
Where we convert lofts
From Finchley N3 we cover North London, North-West London, Central London, South-West and West London, and Hertfordshire — and we also work across the rest of London, Buckinghamshire, Surrey, Kent and Essex. Recent lofts: Hampstead NW6, East Barnet EN4, Putney SW15, Wood Green N22, Borehamwood WD6, Hendon NW4 and Marylebone W1.