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 company · London & Hertfordshire
Loft conversion company London: every type of loft, designed and built by one team
By Anderson & the LCCL Construction Team
Finchley N3 · Design & build, LABC award winners 2024 and 2026
LCCL Construction designs and builds loft conversions across London and Hertfordshire from our base in Finchley N3 — Velux, dormer, L-shaped, hip-to-gable and mansard — with architects, structural engineers and project managers under one contract. Our Weech Road penthouse loft in Hampstead won the LABC Building Excellence Award 2026 for Best Conversion or Alteration to an Existing Home. This page is the overview: the 2026 price for every type, the planning routes, the house types we convert most, and the pages to go to next.
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).
Most loft conversions are permitted development; mansards, flats and conservation-area houses need a planning application. We check your address first.
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
What a loft conversion from LCCL includes
Design and build inclusive — one contract from the survey 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
How much does a loft conversion cost in London in 2026?
Every loft type on one table, design and build inclusive. Every project is priced from your postcode and roof.
Loft conversion type
What it gives you
Guide range
Velux / rooflight
Roof kept, windows in the slope — cheapest, 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)
Also consider
Guide range
On site
Loft + extension together
Roof and ground floor in one programme, one scaffold
See loft + extension
One programme
Whole-flat remodel with the loft
Weech Road NW6 — top-floor flat to penthouse duplex
See home renovation
Phased
House extension instead
Rear, side return, wraparound or two storey
£42,000 – £198,000 inc. VAT (£35,000 – £165,000 + VAT)
10–24 wks
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.
Location: 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 and you receive a detailed itemised estimate — design, planning, structure, construction and warranty priced line by line.
Loft conversions by house type
Victorian or Edwardian terrace
Rear dormer or L-shaped dormer under permitted development (40 m³); mansard where the street pattern supports it. Party wall notices to both neighbours; the steels bear on the party walls.
1930s semi-detached
Hip-to-gable with a rear dormer — the biggest room a hipped roof can give, within 50 m³ under permitted development. Our most common loft in Barnet, Enfield and the Hertfordshire towns.
Top-floor flat or period terrace, Central London
Mansard, with a planning application and often listed building consent — and freeholder consent on a flat. Weech Road NW6 turned a top-floor flat into a penthouse duplex with London views.
Planning
Do you need planning permission for a loft conversion?
Usually not. The type of conversion and the volume decide the route.
Route
Conditions
Time
What we do
1. Permitted development
Rear dormer or hip-to-gable within 40 m³ (terrace) / 50 m³ (semi or detached), no higher than the ridge, set back 20 cm from the eaves, no front dormers on the principal elevation
No application
Lawful Development Certificate, ~8 weeks, included
2. Full planning
Mansards, flats, conservation and Article 4 areas, front dormers, roof raised above the ridge, volume over the limit
8 weeks
Drawings, design statement and application by our team
3. Listed building consent
Listed houses — every external and most internal changes
8 weeks
Heritage statement and application alongside planning
Building regulations & party walls
The other two approvals
Every loft conversion needs building-regulations approval whether or not it needs planning: the new floor, the steels, the stairs, insulation, fire doors and escape windows. We do this through LABC with full-plans drawings and our own structural calculations, so the inspector is checking a design he has already approved.
On a semi or terrace the Party Wall Act applies because the new steels bear on the shared wall. Notices go out at least two months before we start; most neighbours consent, and where a surveyor is appointed we manage it.
Whatever the route, every loft conversion needs building-regulations approval — floor structure, steels, stairs, fire doors, escape windows and insulation — and on a semi or terrace the Party Wall Act applies. We run all three from the same drawings, so nothing is designed twice.
Loft conversion planning permission · How to choose a loft conversion company
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: start the party wall process the week you sign
Most clients underestimate the party wall timeline — on a semi-detached or terraced house it can add three months to the project if it is left until the drawings are finished. We serve the notices at design stage, not build stage, so the two-month notice period runs while the planning application is in.
Talk to the neighbours before the letter lands. A five-minute conversation over the fence, with the drawings in your hand, is the difference between a consent form back in a week and a surveyor's bill.
How a loft conversion runs with LCCL
From the first call to the completion certificate — one team, one contract, one point of contact. Design and approvals typically take 8–12 weeks before work starts.
WEEK 0
Free consultation call
A 30-minute phone call with our team about the house, what you want from the space and a realistic budget. Your instant estimate is the starting point.
WEEKS 1–4
Survey & design
Measured survey, architectural drawings and your detailed itemised estimate — design, planning, structure, construction and warranty priced line by line.
WEEKS 4–12
Approvals
Lawful Development Certificate or planning application, building-regulations drawings, structural calculations, party wall notices. Nothing starts on site until it is signed off.
BUILD
On site
4–16 weeks on site for a loft conversion, depending on the type. Weekly updates from your project manager, one point of contact throughout.
HANDOVER
Sign-off
Snagging, LABC final inspection and completion certificate, guarantees in writing. 10-year LABC structural warranty.
“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
“Extension built by LCCL Construction. We have just recently completed our ground floor house extension on our semi-detached home in Finchley. The services we used were for the design and build of the extension which is three meters and the full breadth of…”
EVA HALL · Trustpilot
“We are very happy with the services from Lccl, Alex has done a great job on design and construction. We have used Lccl in the past for our rear house extension and have come back to instruct Lccl for our loft conversion too to our house in North London. As…”
Mia M · Google Reviews
Loft conversion company questions we get asked most
In 2026, design and build inclusive: Velux £32,400 – £50,400 inc. VAT (£27,000 – £42,000 + VAT), rear dormer £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). Inner and Central London cost more than outer London and Hertfordshire a little less. The instant estimator gives you a figure for your postcode in thirty seconds.
One company and one contract for the architecture, structural engineering, planning, building regulations, party wall and the build. You deal with one project manager from the first sketch to the completion certificate instead of coordinating an architect, an engineer and a loft builder yourself — and the drawings are done by the people who will build from them.
Yes. Our Weech Road penthouse loft conversion in Hampstead NW6 won the LABC Building Excellence Awards 2026 London regional award for Best Conversion or Alteration to an Existing Home, and our Bohun Grove project in East Barnet EN4 — a hip-to-gable loft and rear extension — won the LABC Building Excellence Award 2024 for Best Residential Extension in London.
Usually not. Dormer, L-shaped and hip-to-gable conversions within 40 m³ (terrace) or 50 m³ (semi/detached) are permitted development and we obtain a Lawful Development Certificate. Mansards, flats, conservation and Article 4 areas need a planning application. We check your address before the first drawing.
Four to six weeks on site for a Velux loft, eight to twelve for a dormer, ten to twelve for a hip-to-gable, twelve to sixteen for a mansard, plus 8–16 weeks of design and approvals before that.
Every loft comes with a 12-month workmanship guarantee, and a 10-year LABC structural warranty is available. Building control sign-off is through LABC on every job — we are an LABC Registered Partner.
Yes — over 200 verified reviews at 4.7/5 across Google, Trustpilot, Houzz, Yell and Reviews.io, including Best of Houzz Service every year since 2020. The quotes on this page are taken from those platforms with the reviewer's name and source.
From Finchley N3 we cover all of London and Hertfordshire — North, North-West, Central, South-West and West London most often — and we also work across the rest of London, Buckinghamshire, Surrey, Kent and Essex.
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.