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 value · London & Hertfordshire
How much value does a house extension add in London in 2026?
By Anderson & the LCCL Construction Team
Finchley N3 · Design & build, LABC award winners 2024 and 2026
A well-designed extension is one of the few home improvements in London that reliably adds more than it costs. This page sets out the 2026 cost of each extension type, the value uplift we see on our own projects and on sold prices in the streets we work in, and the design decisions that push the return up or down. We are builders, not valuers — treat every figure as indicative and check it with a local agent before you commit.
Quick answer
£42,000 – £198,000 inc. VAT (£35,000 – £165,000 + VAT) to build, design and build inclusive. The value added on our projects and local sold prices has typically been well above the build cost — most on side returns and two-storey extensions.
The extension type that needs no planning application (single-storey rear or side return within permitted development) is usually the fastest route to added value.
Value is reflected in a valuation as soon as the completion certificate is issued — 10–24 weeks on site plus 8–16 weeks of design and approvals.
A free 30-minute phone call with our team, no obligation.
Build cost
£35,000 – £165,000
Best return
Side return · two storey
Typical build
10–24 weeks on site
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
Cost and typical value added, by extension type
2026 build cost from the price table we build to; the value added is what we have seen on our own projects and on sold prices in the streets we work in. Indicative, not a valuation.
Extension type
Build cost 2026
Value we have seen added
£35,000 – £75,000
£102,000 – £168,000 inc. VAT (£85,000 – £140,000 + VAT) on a £55,000 extension
£42,000 – £93,600 inc. VAT (£35,000 – £78,000 + VAT)
£132,000 – £198,000 inc. VAT (£110,000 – £165,000 + VAT) on a £55,000 extension — the best per pound, because dead alley space becomes living space
£72,000 – £153,600 inc. VAT (£60,000 – £128,000 + VAT)
£156,000 – £306,000 inc. VAT (£130,000 – £255,000 + VAT) on an £85,000 extension
£90,000 – £198,000 inc. VAT (£75,000 – £165,000 + VAT)
£228,000 – £396,000 inc. VAT (£190,000 – £330,000 + VAT) on a £110,000 extension — the largest total uplift, because it adds a bedroom
What moves the value
Effect
Notes
Crossing a price band
Up
Turning a 3-bed into a 4- or 5-bed with a bathroom crosses a band that buyers search in — the biggest single lever
Bedroom plus bathroom
Up
Adds more than ground-floor space alone; two-storey and loft + extension combinations do both
Natural light and glazing
Up
Rooflights over the island, garden doors across the back — the features buyers photograph
Integrated design
Up
An open-plan ground floor reads as one house; a bolted-on box reads as a compromise
Over-development
Down
A 7-bed terrace in a 3-bed street exceeds the street ceiling; returns fall
Garden lost
Down
Outer London buyers value gardens — a 6 m extension on a short garden can cost value
How to work out your own return
Five steps, using the estimator and public sold-price data — no spreadsheet needed.
Step
What to do
Where
2. Current value
Recent sold prices for houses like yours, unextended
Rightmove and Zoopla sold prices, a local agent
3. Extended value
Sold prices for extended houses in your street or the next one
Same sources — look for the same house type with a kitchen extension
4. Uplift
Extended value minus current value
—
5. Return
Uplift divided by build cost
If it is below the build cost, spend less or extend differently
Where our figures come from: the build costs are the 2026 price table we build to — the same table behind the instant estimator and every proposal. The value-added figures are what we have seen on our own completed projects and on sold prices for the streets we work in; they are not a valuation and they vary by street, by finish and by the market on the day. 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 matters twice: the same extension costs more in Inner and Central London and adds proportionally more value, because buyers pay more per square metre. In Hertfordshire the build is about 5% cheaper and the uplift is smaller in pounds but often similar as a share of the house price.
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
Extensions that added value
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: put the rooflights over the island
Rooflights over kitchen islands transform natural light more than any other single design decision. We position them on the plan before the kitchen layout is fixed, not after — moving a rooflight on a drawing costs nothing; moving one in a finished roof costs a week.
The second thing we say on every call: decide where the dining table goes first. Everything else — doors, lighting, the run of the units — follows from that.
“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
House extension value questions we get asked most
Per pound spent, a side return — it turns an unusable alley into a full-width kitchen for £42,000 – £93,600 inc. VAT (£35,000 – £78,000 + VAT). In total pounds, a two-storey extension, because it adds a bedroom as well as ground-floor space and can move the house into a higher price band.
No. It usually does in London when the design is integrated, the light is good and the house stays within the norms of its street. It can fail to when the house is over-developed for the street, the garden is lost, or the finish is poor. Check sold prices for extended houses in your street before you commit.
Look at sold prices for the same house type in your street or the next one with a kitchen extension already done — Rightmove and Zoopla show them — and ask a local agent. That is the honest comparison; a national average is not.
Compare the total cost of moving (stamp duty, agent, legal, removals, and a bigger mortgage) with the build cost and the disruption of 10–24 weeks on site. For most London families who like their street, extending is cheaper and gives them the house they actually want.
They add different things: a loft adds a bedroom and bathroom, an extension adds living space. Doing both in one programme — as at Bohun Grove EN4 — shares the scaffold, the structural design and the party wall process. See our loft-conversion value guide and the loft + extension page.
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.
An extra reception or a bigger kitchen-diner is the improvement most London buyers pay for. Our house-extension value guide sets out what the data shows by area. We are not valuers, so treat any figure as indicative and talk to a local agent before you commit.
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.