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 extension cost · London & Hertfordshire
House extension cost in London 2026: every type priced, and what moves the number
By Anderson & the LCCL Construction Team
Finchley N3 · Design & build, LABC award winners 2024 and 2026
A house extension in London costs £42,000 – £198,000 inc. VAT (£35,000 – £165,000 + VAT) in 2026, design and build inclusive — from a 3 m rear extension to a two-storey side and rear. This page gives you the range for every extension type from the price table we build to, what the figure includes, what pushes it up or down, and how to get an itemised estimate for your own house.
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). Postcode dependent.
Single-storey rear extensions to 3 m (4 m detached) are usually permitted development; 6 m (8 m) by prior approval; wraparounds and two-storey extensions usually need a planning application.
10–14 weeks on site for a single storey, 16–24 weeks for two storeys; 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
How much does a house extension cost in London in 2026?
Guide ranges by extension type, 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, 15–25 m²
£42,000 – £90,000 inc. VAT (£35,000 – £75,000 + VAT)
Width — full-width kitchen on a terrace, 12–20 m²
£42,000 – £93,600 inc. VAT (£35,000 – £78,000 + VAT)
Both — L-shaped open-plan ground floor, 25–40 m²
£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, 30–50 m²
£90,000 – £198,000 inc. VAT (£75,000 – £165,000 + VAT)
Two-storey and combined
Guide range
On site
Double-storey side
Side extension on both floors — an extra bedroom over a wider kitchen
£90,000 – £198,000 inc. VAT (£75,000 – £165,000 + VAT)
18–26 wks
Double-storey side + rear
The largest two-storey combination on a semi
£114,000 – £240,000 inc. VAT (£95,000 – £200,000 + VAT)
20–28 wks
First-floor extension over the outrigger
Bedroom or bathroom over an existing single-storey back addition
£54,000 – £114,000 inc. VAT (£45,000 – £95,000 + VAT)
12–18 wks
Loft + extension together
Roof and ground floor in one programme, one scaffold
See loft + extension
One programme
Where the money goes
What a design and build price is made of, and which lines are priced separately.
Cost element
What it covers
How it is priced
Survey, design and approvals
Measured survey, architectural drawings, planning or lawful development certificate, building-regulations drawings, structural calculations
Included in the design and build price; council application fees at cost
Structural steelwork
Steels, padstones and the engineer's design where the back or outrigger walls come out
Typically £4,800 – £19,200 inc. VAT (£4,000 – £16,000 + VAT) on a Victorian terrace — in every estimate from day one
Shell
Foundations, drainage, walls, roof, rooflights, doors and windows to weather-tight
The largest share — priced from the survey and the drawings, not per m²
First and second fix
Electrics, plumbing, underfloor heating where specified, plaster, decoration, flooring fitted
Included; the items you choose (tiles, flooring, sanitaryware) are supplied by you or through us
Kitchen fit-out
Units, worktops, sink and tap, fitting and connections (appliances, flooring and tiling extra)
£9,000 – £31,200 inc. VAT (£7,500 – £26,000 + VAT) economy, £16,200 – £56,160 inc. VAT (£13,500 – £46,800 + VAT) mid-range, £25,200 – £87,360 inc. VAT (£21,000 – £72,800 + VAT) high-end, by kitchen size — priced as its own line in the instant estimate
Party wall
Notices to each adjoining owner; surveyor only if a neighbour dissents
£300 per notice at cost; surveyor from £750 per neighbour
Location
Access, parking, conservation conditions, logistics
Varies by postcode — the instant estimate applies your area
Added afterwards
—
Nothing: the figure on your itemised estimate is the figure you pay
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: the kitchen itself, supplied and fitted (£9,000 – £87,360 inc. VAT (£7,500 – £72,800 + VAT) by size and specification; appliances extra), flooring 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.
What a house extension from LCCL includes
Design and build inclusive — one contract from the first sketch 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
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.
“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
“Everyone at LCCL Construction was skilled, trustworthy and worked to the highest standard. I am delighted with our loft conversion, it is exactly what we wanted and I highly recommend the company - they have transformed the quality of my home. Overall it…”
KashImaging · Google Reviews
House extension cost questions we get asked most
£42,000 – £90,000 inc. VAT (£35,000 – £75,000 + VAT) in 2026 for a 3–6 m rear extension of 15–25 m², design and build inclusive: a 3 m full-width extension sits around £42,000 – £60,000 inc. VAT (£35,000 – £50,000 + VAT), 4–5 m around £60,000 – £78,000 inc. VAT (£50,000 – £65,000 + VAT), 6 m around £72,000 – £90,000 inc. VAT (£60,000 – £75,000 + VAT). Kitchen units, worktops and appliances are on top.
A 3 m single-storey rear extension or a side-return infill, both from £42,000 inc. VAT (£35,000 + VAT), both usually permitted development so there is no planning application to wait for. The cost per square metre is highest on small extensions because the survey, design, approvals and steelwork cost the same whatever the size.
£90,000 – £198,000 inc. VAT (£75,000 – £165,000 + VAT) for a double-storey rear or side extension, and £114,000 – £240,000 inc. VAT (£95,000 – £200,000 + VAT) for a double-storey side and rear on a semi. Two storeys add a bedroom or bathroom for far less than double the single-storey price because the foundations, drainage and roof are shared.
The kitchen itself, supplied and fitted (£9,000 – £87,360 inc. VAT (£7,500 – £72,800 + VAT) by size and specification; appliances extra), flooring and second-fix items you choose, bespoke joinery, landscaping, council planning fees, and party wall surveyor fees if a neighbour dissents (from £750 per neighbour). Everything else — survey, design, approvals, structure, build, LABC sign-off and guarantees — is in the price.
Yes — every figure is postcode dependent. Parking, access, conservation-area conditions, party wall complexity and logistics all move it, so the instant estimator adjusts the range for your postcode and the detailed itemised estimate follows one survey.
No. The figure on your itemised estimate is the figure you pay — nothing is added afterwards. Items you choose, such as kitchen units or sanitaryware above the allowance, are listed separately before you sign.
Two steps. The instant estimator gives you a range for your postcode and project in thirty seconds. Then one measured survey gives you a detailed itemised estimate — design, planning, structure, construction and warranty priced line by line — with no obligation.
A 12-month workmanship guarantee on every project, with a 10-year LABC structural warranty. Building control sign-off is through LABC — we are an LABC Registered Partner and LABC Building Excellence Award winners in 2024 and 2026.
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, Putney SW15, Mill Hill NW7, Wood Green N22 and Borehamwood WD6.