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.
Loft conversion value · London & Hertfordshire
How much value does a loft conversion add in London in 2026?
By Anderson & the LCCL Construction Team
Finchley N3 · Design & build, LABC award winners 2024 and 2026
A bedroom and bathroom in the roof is the improvement London buyers pay most for, and it usually needs no planning application. This page sets out the 2026 cost of each conversion type, the value uplift we see on our own lofts and on sold prices in the streets we work in, and where the return is strongest. We are builders, not valuers — treat every figure as indicative and check it with a local agent.
Quick answer
£32,400 – £148,800 inc. VAT (£27,000 – £124,000 + VAT) to build, design and build inclusive. On our projects and local sold prices a loft has typically added 10–20% to the value of a London house — well above the build cost.
Velux, dormer, L-shaped and hip-to-gable conversions within 40 m³ (terrace) or 50 m³ (semi/detached) are usually permitted development — no planning application, no delay.
Value is reflected in a valuation as soon as the completion certificate is issued — 4–16 weeks on site plus 8–16 weeks of design and approvals.
A free 30-minute phone call with our team, no obligation.
Build cost
£27,000 – £124,000
Typical uplift
10–20% of house value
Typical build
4–16 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 loft conversion type
2026 build cost from the price table we build to; the value added is what we have seen on our own lofts and on sold prices in the streets we work in. Indicative, not a valuation.
Conversion type
Build cost 2026
Value we have seen added
Velux / rooflight
£27,000 – £42,000
£40,000 – £70,000 on a London terrace
£56,400 – £80,400 inc. VAT (£47,000 – £67,000 + VAT)
£96,000 – £180,000 inc. VAT (£80,000 – £150,000 + VAT) — one bedroom and en-suite
£58,800 – £98,400 inc. VAT (£49,000 – £82,000 + VAT)
£120,000 – £240,000 inc. VAT (£100,000 – £200,000 + VAT) — two bedrooms and two bathrooms on a terrace
£60,000 – £114,000 inc. VAT (£50,000 – £95,000 + VAT)
£108,000 – £192,000 inc. VAT (£90,000 – £160,000 + VAT) — the semi answer
£76,800 – £148,800 inc. VAT (£64,000 – £124,000 + VAT)
£144,000 – £336,000 inc. VAT (£120,000 – £280,000 + VAT) in premium postcodes — the largest absolute uplift
What moves the value
Effect
Notes
A bathroom with the bedroom
Up
A bedroom alone is a box room; a bedroom with an en-suite is a master suite buyers search for
Two rooms rather than one
Up
L-shaped dormers and mansards create two rooms — the 4-bed to 5-bed jump
Head height and stairs
Up or down
A comfortable staircase and full-height space read as a real floor; a ladder-steep stair and a crouch do not
Premium postcode
Up
Same build cost, proportionally larger uplift — Hampstead, Highgate, Islington, Clapham, Fulham
Street ceiling
Down
Above the top price for the street, extra rooms return less
Lost bedroom below
Down
If the new stair takes a first-floor bedroom, count the net gain, not the gross
How to work out your own return
Five steps, using the estimator and public sold-price data.
Step
What to do
Where
2. Current value
Recent sold prices for houses like yours, unconverted
Rightmove and Zoopla sold prices, a local agent
3. Converted value
Sold prices for houses in your street with a loft bedroom
Same sources — look for one extra bedroom and bathroom
4. Uplift
Converted value minus current value
—
5. Return
Uplift divided by build cost
If it is below the build cost, reconsider the type or the finish
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 lofts 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 conversion costs more in Inner and Central London and adds proportionally more, because buyers pay more per square metre there — a dormer that adds £60,000 in one street can add £150,000 in Islington. Hertfordshire builds are about 5% lower-cost.
What a loft conversion from LCCL includes
Design and build inclusive — one contract from the first sketch 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
Lofts 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
%2C%20founder%20of%20LCCL%20Construction.jpeg)
ANDERSON · FOUNDER, LCCL CONSTRUCTION
Anderson's advice: book the design stage in summer, build in autumn
August is our slowest month for project starts — most families delay until the schools go back. That makes it the best time to get the survey, drawings and approvals done: you go through the council queue while everyone else is on holiday and start on site in September or October with the paperwork finished.
Approvals are the part of the programme you cannot compress. Design and planning typically take 8–16 weeks; leave them to the last minute and the build slips into the following year.
“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
“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
Loft conversion value questions we get asked most
The L-shaped dormer and the mansard, because they create the most floor space — two rooms rather than one. In premium London postcodes the mansard gives the largest absolute uplift; on a semi the hip-to-gable with rear dormer is the practical maximum.
Usually in London, when it adds a proper bedroom with a bathroom, the stair is comfortable and the house stays within the price ceiling for its street. It can fail to when the roof is too low for a real room, the new stair costs a bedroom below, or the finish is poor.
Often, yes — from £27,000 it is the lowest-cost way to add a room, and on a tall Victorian roof it can be a good bedroom. It adds less than a dormer because the sloping ceiling limits the usable floor; if head height is marginal, a dormer returns more.
Look at sold prices for the same house type in your street with a loft bedroom already done — Rightmove and Zoopla show them — and ask a local agent. That comparison is worth more than any national average.
If you want both, yes: one scaffold, one structural design, one party wall process and one programme costs less than two projects a year apart. Bohun Grove EN4, our LABC 2024 winner, was a hip-to-gable loft and rear extension together. See 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 convert lofts
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 lofts: Hampstead NW6, East Barnet EN4, Putney SW15, Wood Green N22, Borehamwood WD6, Hendon NW4 and Marylebone W1.