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.
L-shaped loft conversions · London & Hertfordshire
L-shaped loft conversion London: cost, planning rules and build time — from £58,800 inc. VAT (£49,000 + VAT)
By Anderson & the LCCL Construction Team
Finchley N3 · Design & build, LABC award winners 2024 and 2026
An L-shaped dormer joins a rear dormer on the main roof to a second dormer over the outrigger, so the loft follows the L-shaped footprint of a Victorian or Edwardian terrace. It is the way to get two rooms and a bathroom out of a terrace roof — and on most houses it is still permitted development. This page gives you the 2026 numbers, the volume limit that matters on terraces, the layouts that work and how the job runs with one team.
Quick answer
£58,800 – £98,400 inc. VAT (£49,000 – £82,000 + VAT) for an L-shaped dormer loft conversion, design and build inclusive. Postcode dependent.
Usually none: the two dormers together must stay within 40 m³ on a terrace (50 m³ semi). Lawful Development Certificate included.
10–12 weeks on site; 8–12 weeks of design and approvals before that.
A free 30-minute phone call with our team, no obligation.
Guide price
£58,800 – £98,400 inc. VAT (£49,000 – £82,000 + VAT)
Typical build
10–12 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 an L-shaped loft conversion from LCCL includes
Design and build inclusive — the price covers the whole job, 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 an L-shaped loft conversion cost in London in 2026?
Guide ranges, design and build inclusive. Every project is priced from your postcode and house type.
Conversion
Typical use
Guide range
L-shaped dormer, one bedroom + bathroom
Master suite across the main roof, bathroom in the outrigger dormer
£58,800 – £74,400 inc. VAT (£49,000 – £62,000 + VAT)
L-shaped dormer, two bedrooms + bathroom
Bedroom in each wing, bathroom between — the family layout
£72,000 – £88,800 inc. VAT (£60,000 – £74,000 + VAT)
L-shaped dormer, two rooms + bathroom + study
Full use of both wings, new stair, higher specification
£84,000 – £98,400 inc. VAT (£70,000 – £82,000 + VAT)
Related conversion
Guide range
On site
Rear dormer only
Main roof only, outrigger roof kept
£56,400 – £80,400 inc. VAT (£47,000 – £67,000 + VAT)
8–10 wks
Mansard
Both slopes rebuilt — the Central London terrace answer, usually planning
£76,800 – £148,800 inc. VAT (£64,000 – £124,000 + VAT)
12–16 wks
Loft + side return together
Roof and ground floor of the terrace in one programme
See loft + extension
One programme
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.
What moves the price: the length of the outrigger dormer; two roofs rather than one to open, steel and make weather-tight; the junction between the two dormers, which is the trickiest piece of carpentry and lead work on the job; the bathroom and its soil stack; the staircase position; and the finish inside.
L-shaped loft conversions by house type
Victorian terrace with a two-storey outrigger
The classic L-shaped loft. The main-roof dormer takes the master bedroom, the outrigger dormer takes the bathroom or a second bedroom. The 40 m³ terrace allowance is the constraint — we size the outrigger dormer to fit within it, and where it cannot, a planning application for the extra volume is routinely approved outside conservation areas.
Edwardian semi with an outrigger
50 m³ allowance, so the outrigger dormer can be full length and the loft usually gets two bedrooms and a bathroom under permitted development. One party wall notice.
Terrace with a single-storey outrigger
The outrigger roof is too low to convert, so the loft is a plain rear dormer — often with a rear or side return extension below it done at the same time.
Planning
Do you need planning permission for an L-shaped loft conversion?
Usually not — but the 40 m³ terrace limit is tighter for two dormers than one, so we measure before we promise.
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
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; rare on our loft work
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.
Two dormers use the volume allowance faster than one. On a typical terrace the main dormer takes 25–30 m³, leaving 10–15 m³ for the outrigger — usually enough for a bathroom-sized dormer but not always for a full-length one. Where the design needs more, a planning application for the extra volume is routinely approved outside conservation areas; Haringey, Islington and Hackney conservation areas are the exceptions.
L-shaped dormer loft conversion guide · Loft conversion planning permission See our permitted development projects page for every loft and extension you can build without a planning application, with from-prices at economy specification. Not sure whether your project needs a planning application? Check if you need planning permission
Recent L-shaped 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 an L-shaped loft conversion runs with LCCL
From the first call to the completion certificate. Design and approvals typically take 8–12 weeks before work starts; both roofs are opened and made weather-tight in the first three weeks.
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
10–12 weeks on site for an L-shaped dormer loft conversion. Scaffold up, roof opened and made weather-tight, then floor, stairs, first fix, plaster, second fix. Weekly updates from your project manager.
HANDOVER
Sign-off
Snagging, LABC final inspection and completion certificate, guarantees in writing. 10-year LABC structural warranty.
“I highly recommend LCCL Construction. From the start of discussing ideas and planning I can tell you they were very professional and efficient. I had my kitchen and loft done a year ago now and am absolutely thrilled! Exactly what I wanted!”
Nadya Christou · Google Reviews
“We came to LCCL for a full house redesign and renovation after hearing great reviews online and through word of mouth. We couldn't be happier with the outcome. Because of the scale of the project we relied heavily on Alex and the team to provide…”
Steph Brooks · Google Reviews
“We did a 3x10m single storey rear extension with LCCL recently. It was scheduled to take 12 weeks to complete but with Alex's experience and agile project management, we are ahead of schedule (finished in 10). Alex, and LCCL,is extremely knowledgeable and…”
Christophe · Trustpilot
L-shaped loft conversion questions we get asked most
£58,800 – £98,400 inc. VAT (£49,000 – £82,000 + VAT) in 2026, design and build inclusive — survey, drawings, lawful development certificate, structural calculations, both dormer structures, stairs, insulation, first and second fix, decoration, a bathroom where specified and LABC sign-off. One bedroom with a bathroom sits at the bottom of the range; two bedrooms, a bathroom and a study at the top.
A rear dormer on the main roof joined to a second dormer over the two-storey outrigger of a Victorian or Edwardian terrace, so the loft is L-shaped on plan. It is the only way to get two proper rooms out of a terrace roof without a mansard.
On most terraces, no — if both dormers together stay within 40 m³ (50 m³ on a semi). We measure the roof on the survey. Where the outrigger dormer would take the total over the limit, a planning application for the extra volume is routinely approved outside conservation areas.
Ten to twelve weeks on site, plus 8–12 weeks before that for design and approvals. Two roofs are opened rather than one, so the weather-tight stage takes about a week longer than a single dormer.
On most terraces, yes: a bedroom in each wing and the bathroom between them, or the bathroom in the outrigger dormer. The outrigger wing is narrower than the main roof, so the second bedroom is usually the smaller of the two.
Yes, on both sides — the main-roof steels bear on both party walls and the outrigger dormer sits against the neighbour's outrigger. We serve the notices at cost (£300 each) at design stage; on a terrace this is the item that most often delays a start if it is left late.
The outrigger roof is usually lower than the main roof, so we check it separately on the survey. Where it has less than about 2.1 m to the ridge, the outrigger dormer is sized for a bathroom rather than a bedroom, or the outrigger roof is rebuilt as part of the works.
On a terrace outside Central London, the L-shaped dormer under permitted development. A mansard gives a little more space but needs planning and costs more; it makes sense where mansards are the street pattern, as in much of Westminster, Camden and Kensington. We compare both on the consultation call.
Where we build L-shaped loft conversions
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 L-shaped lofts: Wood Green N22 and the Victorian terraces of North and North-West London.