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.
Side return extension cost · London & Hertfordshire
Side return extension cost in London 2026: £42,000 – £93,600 inc. VAT (£35,000 – £78,000 + VAT), and what decides where you land
By Anderson & the LCCL Construction Team
Finchley N3 · Design & build, LABC award winners 2024 and 2026
A side return extension in London costs £42,000 – £93,600 inc. VAT (£35,000 – £78,000 + VAT) in 2026, design and build inclusive. The alley beside a Victorian or Edwardian outrigger becomes a full-width kitchen — the best-value square metres most terraces have. This page gives you the range by size, what is in the figure, what moves it, and how to get an itemised estimate for your house.
Quick answer
£42,000 – £93,600 inc. VAT (£35,000 – £78,000 + VAT) for a single-storey side return extension, design and build inclusive (kitchen on top). Postcode dependent.
Usually permitted development on a terrace or semi within the 3 m / 4 m limits; we obtain a Lawful Development Certificate. Conservation and Article 4 areas need a planning application.
10–14 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
£42,000 – £93,600 inc. VAT (£35,000 – £78,000 + VAT)
Typical build
10–14 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 side return extension cost in London in 2026?
Guide ranges by size, design and build inclusive. Every project is priced from your postcode and house type.
Side return
Typical use
Guide range
Infill only (≈8–12 m²)
Galley kitchen widened to full width, glazed roof
£42,000 – £60,000 inc. VAT (£35,000 – £50,000 + VAT)
Infill + knock-through (≈12–18 m²)
Kitchen and dining opened into one room, steel across the outrigger wall
£57,600 – £78,000 inc. VAT (£48,000 – £65,000 + VAT)
Infill + rear step-out (≈18–25 m²)
Side return plus 1–2 m beyond the outrigger — an L-shaped rear
£72,000 – £93,600 inc. VAT (£60,000 – £78,000 + VAT)
Related extension
Guide range
On site
Rear extension
Depth rather than width — 3–6 m beyond the back wall
£42,000 – £90,000 inc. VAT (£35,000 – £75,000 + VAT)
10–14 wks
Wraparound extension
Side return and rear together, one scaffold, one contract
£72,000 – £153,600 inc. VAT (£60,000 – £128,000 + VAT)
14–18 wks
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.
What moves the price: the length of the side return and whether you step out beyond the outrigger; the roof — a fully glazed roof or a run of rooflights against a flat roof with a lantern; how much of the outrigger wall comes out and the steel that replaces it (on a Victorian terrace typically £4,800 – £19,200 inc. VAT (£4,000 – £16,000 + VAT)); drainage running under the new floor and whether a Thames Water build-over agreement is needed; and the finish level inside. 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.
What the price 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 side return 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.
“We engaged with LCCL Construction to get our loft conversion and house extension project going. The whole process was explained to us in a straight forward way including how the design stages work, timescales, what to expect during the build and the costs…”
Daniel Freedman · Trustpilot
“I highly recommend LCCL Construction. They completed our loft conversion to a very high standard, and the quality of workmanship throughout was excellent. The team was professional, reliable, and completed everything within a very reasonable timeframe.…”
Alina A · Google Reviews
“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…”
Plamen Petrov · Trustpilot
Cost questions we get asked most
We do not price per square metre because the fixed costs — survey, design, approvals, steelwork — are the same on an 8 m² infill as on a 25 m² one. That is why a small infill can look expensive per m² and a side return with a rear step-out looks low-cost. The size table above is the honest guide.
About the same range — £35,000–£78,000 against £42,000 – £90,000 inc. VAT (£35,000 – £75,000 + VAT) — but the side return usually adds more usable width to a terrace kitchen for the money, and it takes no garden. A wraparound (£72,000 – £153,600 inc. VAT (£60,000 – £128,000 + VAT)) does both.
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, council fees, and party wall surveyor fees if a neighbour dissents (from £750). Survey, design, approvals, structure, build, LABC sign-off and guarantees are in the price.
Usually not on a terrace or semi — it is permitted development within the limits and we obtain a Lawful Development Certificate. Conservation areas, Article 4 areas and flats need a planning application; we check your address before the first drawing.
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
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.