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.
Hip to gable loft conversions · London & Hertfordshire
Hip to gable loft conversion London: cost, planning rules and build time — from £60,000 inc. VAT (£50,000 + VAT)
By Anderson & the LCCL Construction Team
Finchley N3 · Design & build, LABC award winners 2024 and 2026
A hip-to-gable conversion rebuilds the sloping side of a hipped roof as a vertical gable wall, which turns the wasted triangle at the end of a 1930s semi or detached house into full-height floor space. Combined with a rear dormer it gives the biggest loft a hipped roof can produce — and on most houses it is still permitted development. This page gives you the 2026 numbers, the planning limits, the house types it suits and how the job runs with one team.
Quick answer
£60,000 – £114,000 inc. VAT (£50,000 – £95,000 + VAT) for a hip-to-gable loft conversion, usually with a rear dormer, design and build inclusive. Postcode dependent.
Usually none on a semi or detached house: hip-to-gable plus rear dormer within 50 m³ is permitted development. 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
£60,000 – £114,000 inc. VAT (£50,000 – £95,000 + 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 a hip to gable 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 hip to gable 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
Hip-to-gable only
Gable end rebuilt, Velux windows, one large bedroom
£60,000 – £74,400 inc. VAT (£50,000 – £62,000 + VAT)
Hip-to-gable + rear dormer
Master bedroom with en-suite and a full-height rear wall — the standard semi conversion
£72,000 – £96,000 inc. VAT (£60,000 – £80,000 + VAT)
Double hip-to-gable + dormer (detached)
Both hips rebuilt, two bedrooms and a bathroom
£90,000 – £114,000 inc. VAT (£75,000 – £95,000 + VAT)
Related conversion
Guide range
On site
Rear dormer only
Keeps the hip; smaller room, lower cost
£56,400 – £80,400 inc. VAT (£47,000 – £67,000 + VAT)
8–10 wks
Mansard
New roof across the whole footprint — the most space, usually planning
£76,800 – £148,800 inc. VAT (£64,000 – £124,000 + VAT)
12–16 wks
Loft + rear extension together
The Bohun Grove EN4 combination under 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: whether the rear dormer is included (it nearly always should be); the gable wall — blockwork rendered or brick to match the house; the steels, which are longer on a semi because the new floor spans to the new gable; the bathroom; the staircase position; and whether the front slope is re-tiled to match the new gable.
Hip to gable loft conversions by house type
1930s semi-detached
The house this conversion was made for. The side hip becomes a gable, the rear dormer runs full width, and the result is a master bedroom with en-suite that most semis cannot get any other way. Within 50 m³ it is permitted development; the attached neighbour gets a party wall notice. Barnet, Enfield and the Hertfordshire towns are full of these.
Detached with a hipped roof
Both hips can be rebuilt (a double hip-to-gable) within the same 50 m³ allowance on most houses, giving two bedrooms and a bathroom. Height to the ridge is unchanged, so the eaves detail and the roof covering are the main design decisions.
End-of-terrace with a hipped end
Treated like a semi: one gable rebuilt, one party wall. The 40 m³ terrace allowance applies, so the dormer is sized to fit within it.
Planning
Do you need planning permission for a hip to gable loft conversion?
Usually not on a semi or detached house. The 50 m³ allowance covers a hip-to-gable and a rear dormer together on most roofs.
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 things catch hip-to-gable schemes: the new gable must not be higher than the existing ridge, and in some boroughs a side-facing gable on a corner plot counts as a principal elevation and needs planning. We check both on the survey and obtain the Lawful Development Certificate as part of the design stage.
Hip to gable loft conversion cost 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 hip to gable 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 hip to gable 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 gable is built and the roof 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 a hip-to-gable loft conversion with rear dormer. 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 couldn't be happier with my loft conversion and extension done by LCCL Building Construction. Real craftsmanship, professional management of the entire build from start to finish, seamless integration of new space within the existing one. The work was…”
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“LCCL Construction has beautifully transformed our house with a loft conversion, house extension and renovation including design and build, we are amazed with high quality of the build, professionalism and dedication to successfully complete our highly…”
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“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…”
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Hip to gable loft conversion questions we get asked most
£60,000 – £114,000 inc. VAT (£50,000 – £95,000 + VAT) in 2026, design and build inclusive — survey, drawings, lawful development certificate, structural calculations, the new gable and dormer structure, stairs, insulation, first and second fix, decoration, a bathroom where specified and LABC sign-off. Hip-to-gable with a rear dormer and en-suite on a semi is typically £72,000 – £96,000 inc. VAT (£60,000 – £80,000 + VAT).
On most semis and detached houses, no. A hip-to-gable with a rear dormer within 50 m³, no higher than the ridge, is permitted development and we obtain a Lawful Development Certificate. Conservation areas, Article 4 areas, flats and some corner plots need a planning application.
Ten to twelve weeks on site, plus 8–12 weeks before that for design and approvals. It is two weeks longer than a plain dormer because the gable wall is built first and the roof is re-formed against it.
Almost always. The hip-to-gable creates the floor area; the rear dormer creates the full-height wall that makes it a proper bedroom and fits the en-suite. Doing both together costs modestly more than the hip-to-gable alone and far less than adding the dormer later.
It can be brick to match, or render, or tile-hung to match a tile-hung gable next door. Planning does not require a match when it is permitted development, but the street usually looks better for it and we price both.
On a semi, yes — the new floor steels bear on the party wall. We serve the notice at cost (£300) at design stage so the two-month period runs alongside the approvals. Most neighbours consent; talking to them before the letter lands is the single best thing you can do.
The test is 2.2 m from the top of the ceiling joists to the ridge. Most 1930s semis pass it. Because the gable does not change the ridge height, a low roof cannot be fixed by this conversion alone — raising the ridge needs planning and we price it separately.
On a semi in a normal street, hip-to-gable plus dormer under permitted development. A mansard gives more space but almost always needs planning and costs more; it makes sense on terraces in Central London where mansards are the local pattern. We compare both on the consultation call.
Where we build hip to gable 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 hip-to-gable lofts: East Barnet EN4, Borehamwood WD6 and Hendon NW4.