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.
House extensions · London & Hertfordshire
House extensions London: every type, priced, planned 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 house extensions across London and Hertfordshire from our base in Finchley N3 — rear, side return, wraparound, kitchen and two storey — with architects, structural engineers and project managers under one contract. This page is the overview: the 2026 price for every type, the planning routes, the house types we build on most, and the pages to go to next.
Quick answer
£42,000 – £198,000 inc. VAT (£35,000 – £165,000 + VAT) design and build inclusive, depending on the type: single-storey from £42,000 inc. VAT (£35,000 + VAT), wraparound from £72,000 inc. VAT (£60,000 + VAT), two storey from £90,000 inc. VAT (£75,000 + VAT).
Most single-storey extensions are permitted development; wraparounds and two storey extensions usually need a planning application. We check your address first.
10–24 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
£42,000 – £198,000 inc. VAT (£35,000 – £165,000 + VAT)
Typical build
10–24 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 house extension from LCCL includes
Design and build inclusive — one contract from the survey to the completion certificate.
Measured survey of the house and garden
Architectural design and drawings, with revisions until you're happy
Planning application or Lawful Development Certificate, 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)
Foundations, drainage and any build-over agreement with Thames Water
Structure, roof, rooflights, doors and windows to a weather-tight shell
Plaster finish, first-fix electrics and plumbing, underfloor heating where specified
Fitting of the kitchen, flooring and second-fix items you supply
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 house extension cost in London in 2026?
Every extension type on one table, design and build inclusive. Every project is priced from your postcode and house type.
Extension type
What it gives you
Guide range
Rear extension 3–6 m
Depth — kitchen-diner and garden doors
£42,000 – £90,000 inc. VAT (£35,000 – £75,000 + VAT)
Width — full-width kitchen on a terrace
£42,000 – £93,600 inc. VAT (£35,000 – £78,000 + VAT)
Both — L-shaped open-plan ground floor
£72,000 – £153,600 inc. VAT (£60,000 – £128,000 + VAT)
Any shape, plus the fit-out priced separately
£42,000 – £153,600 inc. VAT (£35,000 – £128,000 + VAT) + £9,000 – £87,360 inc. VAT (£7,500 – £72,800 + VAT)
Kitchen below, bedroom or bathroom above
£90,000 – £198,000 inc. VAT (£75,000 – £165,000 + VAT)
Also consider
Guide range
On site
Loft conversion
Bedroom and bathroom in the roof, usually permitted development
£32,400 – £148,800 inc. VAT (£27,000 – £124,000 + VAT)
4–16 wks
Loft + extension together
Ground floor and roof in one programme, one scaffold
See loft + extension
One programme
Whole-house renovation with extension
Bohun Grove EN4 — extension, loft, renovation and landscaping
£474,000 – £570,000 inc. VAT (£395,000 – £475,000 + VAT)
Phased
What the price includes: survey, architectural drawings, planning or lawful development certificate, building-regulations drawings, structural calculations, construction to plaster finish with first-fix electrics and plumbing, LABC sign-off and guarantees. On top: kitchen, bathroom and second-fix items you choose. 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.
House extensions by house type
Victorian or Edwardian terrace
Side return, rear to the outrigger, or both as a wraparound. Permitted development covers the side return and a rear extension to 3 m; a wraparound usually needs planning. Party wall notices to both neighbours. Steel across the outrigger wall is the main structural cost — typically £4,800 – £19,200 inc. VAT (£4,000 – £16,000 + VAT).
1930s semi-detached
Full-width rear extension of 3–4 m, or a two storey rear with a bedroom above. Rear to 3 m is permitted development, 6 m by prior approval; two storey almost always needs planning. Our most common house type in Barnet, Enfield and Hertfordshire.
Detached house
Rear extension to 4 m under permitted development, 8 m by prior approval; two storey sometimes permitted development if the garden is deep enough. Larger glazing spans mean heavier steel — budget for it early.
Planning
Do you need planning permission for a house extension?
Usually not for a single-storey extension. The type and the depth decide the route.
Route
Applies to
Time
What we do
1. Permitted development
Single-storey rear to 3 m (4 m detached); side return within limits
No application
Lawful Development Certificate, ~8 weeks, included
2. Prior approval
Single-storey rear to 6 m (8 m detached)
42 days
Larger home extension submission with neighbour notification
3. Full planning
Wraparounds, two storey, flats, conservation and Article 4 areas
8 weeks
Drawings, design statement and application by our team
Building regulations & party walls
The other two approvals
Every extension needs building-regulations approval whether or not it needs planning: foundations, structure, insulation, glazing area, drainage and fire. 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, not improvising on site.
If the extension is on or near the boundary of a semi or terrace, the Party Wall Act applies. 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 extension needs building-regulations approval, and on a semi or terrace the Party Wall Act applies. We run all three — planning, building regulations, party wall — from the same drawings, so nothing is designed twice.
House extension planning permission · Permitted development rights guide
Recent house extension 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: budget for the steelwork, not just the kitchen
Clients budget for kitchen units but forget the structural steelwork when opening up ground-floor walls. On a Victorian terrace that is typically £4,800 – £19,200 inc. VAT (£4,000 – £16,000 + VAT) for the load-bearing opening, depending on its width — we price it on every proposal so there is no surprise.
Get the structural design done early, from a measured survey, and the steel arrives on site the week it is needed rather than holding the programme.
How a house extension runs with LCCL
From the first call to the completion certificate — one team, one contract, one point of contact. Design, planning and building regulations typically take 8–16 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
10–24 weeks on site for a house extension, 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.
“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…”
Leonard Shehu · 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…”
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“Contracted lccl construction to design and build hip to gable loft conversion, after much research I found Lccl construction to be the most efficient and reliable company to deal with, the initial design phases started immediately their architects attended…”
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House extension questions we get asked most
In 2026, design and build inclusive: a single-storey rear or side return extension £42,000 – £93,600 inc. VAT (£35,000 – £78,000 + VAT), a wraparound £72,000 – £153,600 inc. VAT (£60,000 – £128,000 + VAT), a two storey extension £90,000 – £198,000 inc. VAT (£75,000 – £165,000 + VAT). Inner and Central London cost more than outer London and Hertfordshire a little less. The kitchen and bathroom fit-out is priced on top. 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 construction itself. You deal with one project manager from the first sketch to the completion certificate instead of coordinating an architect, an engineer and a builder yourself.
Usually not for a single-storey rear or side return extension — they are permitted development and we obtain a Lawful Development Certificate. Wraparounds, two storey extensions, flats and conservation-area houses need a full application with an eight-week decision. We check your address before the first drawing.
Ten to fourteen weeks on site for a single-storey rear or side return, fourteen to eighteen for a wraparound, sixteen to twenty-four for two storey, plus 8–16 weeks of design and approvals before that.
An open-plan kitchen-diner is what London buyers pay for, so the extension that creates one — rear, side return or wraparound depending on the house — is usually the best return. Our house-extension value guide sets out what the data shows by area. We are not valuers; talk to a local agent before you commit.
Yes. LCCL Construction won the LABC Building Excellence Award 2024 for Best Residential Extension in London for the Bohun Grove project in East Barnet EN4, and the LABC Building Excellence Awards 2026 London regional award for Best Conversion or Alteration to an Existing Home for Weech Road, Hampstead NW6.
Every project 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.
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 build house extensions
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 extensions: East Barnet EN4, Finchley N3, Mill Hill NW7, Chelsea SW10, Putney SW15 and Crouch End N8.