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.
Dormer loft conversions · London & Hertfordshire
Dormer loft conversion London: cost, planning rules and build time — from £56,400 inc. VAT (£47,000 + VAT)
By Anderson & the LCCL Construction Team
Finchley N3 · Design & build, LABC award winners 2024 and 2026
A rear dormer is the most common loft conversion in London: a box structure built out from the back slope of the roof that turns a cramped attic into a full-height bedroom, usually with an en-suite. It is almost always permitted development. This page gives you the 2026 numbers, the volume limits that decide whether you need planning, what changes on a terrace, semi or detached house, and how the job runs with one team.
Quick answer
£56,400 – £80,400 inc. VAT (£47,000 – £67,000 + VAT) for a rear dormer loft conversion, design and build inclusive, bathroom where specified. Postcode dependent.
Usually none: a rear dormer within 40 m³ (terrace) or 50 m³ (semi/detached) is permitted development. Lawful Development Certificate included.
8–10 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
£56,400 – £80,400 inc. VAT (£47,000 – £67,000 + VAT)
Typical build
8–10 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 dormer 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 a dormer loft conversion cost in London in 2026?
Guide ranges, design and build inclusive. Every project is priced from your postcode and house type.
Dormer
Typical use
Guide range
Small rear dormer (bedroom only, Velux to the front)
Double bedroom, no bathroom, existing stair position
£56,400 – £64,800 inc. VAT (£47,000 – £54,000 + VAT)
Full-width rear dormer with en-suite
Master bedroom and shower room — the standard London loft
£62,400 – £74,400 inc. VAT (£52,000 – £62,000 + VAT)
Full-width dormer, two rooms
Two bedrooms or bedroom plus study, bathroom, new stair
£69,600 – £80,400 inc. VAT (£58,000 – £67,000 + VAT)
Related conversion
Guide range
On site
L-shaped dormer
Rear dormer plus a dormer over the outrigger — the terrace upgrade
£58,800 – £98,400 inc. VAT (£49,000 – £82,000 + VAT)
10–12 wks
Hip-to-gable + rear dormer
The semi-detached combination — biggest room for the money
£60,000 – £114,000 inc. VAT (£50,000 – £95,000 + VAT)
10–12 wks
Velux / rooflight loft
Roof structure kept, windows in the slope — lowest-cost option
£32,400 – £50,400 inc. VAT (£27,000 – £42,000 + VAT)
4–6 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.
What moves the price: the size of the dormer and whether it is full width; the bathroom (a shower room adds drainage, a soil stack and a second fix that a bedroom-only loft does not have); where the new staircase lands — over the existing stair is lowest-cost, taking a slice of a bedroom costs more; steels spanning between party walls; the roof covering and whether the front slope needs re-tiling; and the finish inside.
Dormer loft conversions by house type
Victorian or Edwardian terrace
The rear dormer sits on the main roof and the outrigger roof is usually left as it is — or converted too as an L-shaped dormer. The 40 m³ limit is the number to watch on a terrace; most full-width dormers fit within it. Two party wall notices.
1930s semi
A rear dormer on its own works, but on a hipped roof the hip-to-gable and rear dormer combination gives a far bigger room for a modest extra cost and still fits within 50 m³ under permitted development.
Detached house
50 m³ allowance and usually a bigger roof, so a full-width dormer with two rooms and a bathroom is common. Height to the ridge is the limit — the dormer cannot go above it.
Planning
Do you need planning permission for a dormer loft conversion?
Usually not. Rear dormers are the loft conversion most often built under permitted development.
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.
The volume allowance counts every roof enlargement on the house since it was built, so an earlier extension with a pitched roof may have used part of it. We measure it on the survey and obtain the Lawful Development Certificate as part of the design stage — it is the document that proves the loft was lawful when you sell.
Loft conversion planning permission guide · Dormer loft conversion guide 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 dormer 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.
How a dormer loft conversion runs with LCCL
From the first call to the completion certificate. Design and approvals typically take 8–12 weeks before work starts; the scaffold goes up on day one and the roof is opened and made weather-tight in the first fortnight.
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
8–10 weeks on site for a rear 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.
“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.”
Mia M · Google Reviews
“The Lccl construction team built my extension with a quick and clean service, they worked non stop through the winter weather.. I would highly recommend this company!”
Chris Dunn · Google Reviews
“LCCL Construction was the right company to help with my loft conversion. I heard of other people's challenging experiences with building works so I was very careful which company I chose. LCCL Constructions was professional, trustworthy and worked to the…”
KashImaging · Trustpilot
Dormer loft conversion questions we get asked most
£56,400 – £80,400 inc. VAT (£47,000 – £67,000 + VAT) in 2026, design and build inclusive — survey, drawings, lawful development certificate, structural calculations, the dormer structure, stairs, insulation, first and second fix, decoration, a bathroom where specified and LABC sign-off. A small rear dormer without a bathroom sits at the bottom of the range; a full-width dormer with two rooms and a bathroom at the top.
On most houses, no. A rear dormer within 40 m³ on a terrace or 50 m³ on a semi or detached house, no higher than the existing ridge and set back 20 cm from the eaves, is permitted development. We obtain a Lawful Development Certificate. Flats, conservation areas, Article 4 areas and front dormers need a planning application.
Eight to ten weeks on site, plus 8–12 weeks before that for design and approvals. The roof is opened and made weather-tight in the first two weeks, so the disruption inside the house is concentrated into the stair installation and the last fortnight.
The usual test is 2.2 m from the top of the existing ceiling joists to the underside of the ridge; a dormer then gives full head height across most of the room. Below about 2.1 m the options are lowering the ceilings below or raising the roof, both of which we price separately. We measure it on the survey.
Yes — most of our dormer lofts have one. The shower room usually sits at the low-headroom side under the slope, with the soil stack dropping into the existing bathroom below. It adds drainage, a second fix and a few thousand pounds to the price.
Over the existing staircase wherever the layout allows, which costs the least space and money. Where it cannot, the new stair takes a slice of the rear bedroom. We draw both options at survey stage so you can see what each one costs in floor area.
On a semi or terrace, yes — the new steels bear on the shared wall. Notices go out at least two months before work starts; we serve them at cost (£300 each) at design stage. Most neighbours consent without appointing a surveyor.
On a terrace with a gable roof, a rear dormer (or an L-shaped dormer if you have an outrigger) is the answer. On a semi or detached house with a hipped roof, the hip-to-gable and rear dormer combination gives a far bigger room for a modest extra cost. The consultation call settles it for your roof.
Where we build dormer 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 dormer lofts: Putney SW15, Wood Green N22 and East Barnet EN4.