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 + extension together · London & Hertfordshire
Loft conversion and extension together: one programme, one scaffold, one contract
By Anderson & the LCCL Construction Team
Finchley N3 · Design & build, LABC award winners 2024 and 2026
Doing the loft and the extension in one project is how most of our biggest transformations happen — Bohun Grove EN4, our LABC 2024 award winner, was a hip-to-gable loft, a rear extension and a whole-house renovation under one contract. It costs less than doing them a year apart because the scaffold, the structural design, the party wall process and the disruption are shared. This page gives you the combined 2026 numbers, the combinations that work on each house type, how the two planning routes fit together and how the build is sequenced.
Quick answer
Add the two guide ranges: for example a rear extension (£35,000–£75,000) plus a rear dormer (£56,400 – £80,400 inc. VAT (£47,000 – £67,000 + VAT)) is typically £98,400 – £170,400 inc. VAT (£82,000 – £142,000 + VAT) combined, design and build inclusive. Postcode dependent.
Each part takes its own route: the loft is usually permitted development; the extension is permitted development, prior approval or planning depending on its shape.
One programme, run in parallel — usually the longer of the two build times plus a few weeks, not the two added together.
A free 30-minute phone call with our team, no obligation.
Guide price
From £98,400 inc. VAT (£82,000 + VAT) combined
Typical build
One programme, overlapping
Guarantee
12-month workmanship guarantee; 10-year LABC structural warranty
Awards
LABC 2024 winner — Bohun Grove EN4
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 combined loft and extension from LCCL includes
Everything on both service pages, under one contract and one project manager.
Measured survey of the whole house, roof and garden
One set of architectural drawings covering the loft and the extension, with revisions until you're happy
One planning package: Lawful Development Certificate for the loft; LDC, prior approval or planning application for the extension
One set of building-regulations drawings and structural calculations — the steels for both are designed together
One round of party wall notices covering both parts (£300 each, at cost)
Foundations, drainage and the extension shell to weather-tight
New loft floor, steels, dormer or gable structure, roof and windows
Staircase, insulation, fire doors and escape windows for the loft; glazing and rooflights for the extension
Plaster finish, first-fix electrics and plumbing throughout; bathrooms and kitchen fitted where specified
LABC inspections and one completion certificate
A dedicated project manager and a weekly progress update
12-month workmanship guarantee; 10-year LABC structural warranty
How much do a loft conversion and extension cost together in London in 2026?
Add the two guide ranges, then expect the combined figure to sit towards the lower end because the shared items are priced once.
Combination
Typical use
Combined guide range
Rear extension + rear dormer
Kitchen-diner below, master suite in the roof — the semi and terrace standard
£98,400 – £170,400 inc. VAT (£82,000 – £142,000 + VAT)
Side return + L-shaped dormer
Full-width kitchen and two loft rooms on a Victorian terrace
£100,800 – £192,000 inc. VAT (£84,000 – £160,000 + VAT)
Rear extension + hip-to-gable dormer
The Bohun Grove EN4 combination on a 1930s semi
£102,000 – £204,000 inc. VAT (£85,000 – £170,000 + VAT)
Wraparound + loft
Whole ground floor and roof — a three-bed becomes a five-bed
£128,400 – £267,600 inc. VAT (£107,000 – £223,000 + VAT)
What is shared
Saving
Notes
Scaffold
One hire instead of two
The single biggest saving — a full scaffold is needed for both parts
Structural design and party wall
One engineer's package, one round of notices
The loft steels and the extension steels are designed as one structure
Disruption
One period of works, one temporary kitchen
Live through it once, not twice, a year apart
What the price includes: everything on the individual loft and extension pages — survey, drawings, all approvals, structural calculations, both structures to plaster finish with first-fix electrics and plumbing, stairs, insulation, fire safety, 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), sanitaryware above the allowance, 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 size of each part, exactly as on the individual pages; how much of the existing house between them is remodelled (moving the stair, opening the ground floor, new bathrooms); and the finish level. Bohun Grove EN4 — extension, loft, whole-house renovation and landscaping — was a £474,000 – £570,000 inc. VAT (£395,000 – £475,000 + VAT) project; a straightforward rear extension plus dormer on a terrace sits near the bottom of the table.
Loft + extension combinations by house type
Victorian terrace
Side return or rear extension below, rear dormer or L-shaped dormer above. Both parts are usually permitted development; the extension takes the LDC route and the loft its own LDC. Two party wall notices cover both.
1930s semi
Full-width rear extension below, hip-to-gable with rear dormer above — the Bohun Grove EN4 combination. The extension is PD to 3 m or prior approval to 6 m; the loft is PD within 50 m³. One party wall notice to the attached neighbour covers both.
Rear extension · Hip-to-gable loft · Bohun Grove EN4 project
Two storey extension instead
Where the garden allows, a two storey rear gives the kitchen and the bedroom in one structure — but it almost always needs planning, where the loft + single-storey route usually does not. We compare both on the consultation call.
Planning
Do you need planning permission for a loft and extension together?
Each part is assessed on its own rules. Doing them together does not change the route for either — but it does let us submit them together.
Part
Usual route
Time
What we do
Loft (dormer, L-shaped, hip-to-gable)
Permitted development within 40/50 m³
No application
Lawful Development Certificate, ~8 weeks, included
Single-storey extension to 3 m (4 m detached)
Permitted development
No application
Lawful Development Certificate, submitted with the loft's
Single-storey extension to 6 m (8 m detached)
Prior approval
42 days
Larger home extension submission with neighbour notification
Wraparound, two storey, mansard, conservation areas
Full planning
8 weeks
One application covering both parts where the council allows
Building regulations & party walls
The other two approvals
Both parts need building-regulations approval — foundations, structure, insulation, drainage and fire for the extension; floor, steels, stairs, fire doors and escape windows for the loft — and because the loft adds a storey, the fire escape route through the whole house is assessed as one. We do this through LABC with full-plans drawings and one structural package.
On a semi or terrace the Party Wall Act applies to both parts; one round of notices, served at design stage, covers the excavation below and the steels above.
One thing to watch: the permitted development volume allowance for the loft and the half-garden rule for the extension are both measured against the original house, and an extension with a pitched roof can use part of the loft allowance. We check both on the survey so neither part is designed on an assumption the other breaks.
Loft conversion or extension — which first? · Loft conversion vs extension Not sure whether your project needs a planning application? Check if you need planning permission
Recent loft + 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
%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.
How a combined loft and extension runs with LCCL
One programme. The extension groundworks and the loft roof works start together under one scaffold; the two shells are made weather-tight, then first fix, plaster and second fix run through the whole house.
WEEK 0
Free consultation call
A 30-minute phone call with our team about the house, both parts of the project and a realistic budget. Your instant estimate for each part is the starting point.
WEEKS 1–4
Survey & design
Measured survey of the whole house, one set of drawings covering the loft and the extension, and your detailed itemised estimate — both parts priced line by line so you can see what each costs and what is shared.
WEEKS 4–12
Approvals
Lawful Development Certificates, prior approval or planning application as each part needs, one building-regulations package, one structural package, one round of party wall notices. Nothing starts on site until both are signed off.
BUILD
On site
Typically 14–20 weeks for a rear extension plus dormer on one programme: scaffold, groundworks and roof works together, both shells weather-tight, then first fix, plaster and second fix through the house. Weekly updates from your project manager.
HANDOVER
Sign-off
Snagging, LABC final inspection and one completion certificate, guarantees in writing. 10-year LABC structural warranty.
“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
Loft + extension questions we get asked most
Add the two 2026 guide ranges and expect the total to sit towards the lower end: a rear extension plus rear dormer is typically £98,400 – £170,400 inc. VAT (£82,000 – £142,000 + VAT), side return plus L-shaped dormer £100,800 – £192,000 inc. VAT (£84,000 – £160,000 + VAT), rear extension plus hip-to-gable £102,000 – £204,000 inc. VAT (£85,000 – £170,000 + VAT), all design and build inclusive. Kitchen and sanitaryware are on top.
Yes. The scaffold is hired once, the structural design and party wall process are done once, and you live through one period of works instead of two. The saving is real but modest — the main reason to combine them is that the two structures are designed as one, so the loft steels and the extension steels do not fight each other.
Usually the extension, because it changes the ground floor you live in every day and its structure is what the loft will later sit on. But if the roof is the bigger problem — a growing family and no bedroom — the loft first, designed so the extension can follow. Our guide on which to do first covers the trade-offs.
Each part follows its own rules. The loft is usually permitted development; a single-storey extension to 3 m is permitted development, to 6 m is prior approval; a wraparound or two storey extension needs a full application. Doing them together does not change either route, but we submit them together.
Usually the longer of the two build times plus a few weeks, not the two added together — typically 14–20 weeks on site for a rear extension plus dormer, run as one programme. Design and approvals take 8–16 weeks before that.
Most clients do. The extension shell is built before the back wall comes out, and the loft is opened under scaffold before the stair comes through, so the house keeps a working kitchen and bedrooms for most of the programme. We agree the two disruptive weeks with you in advance.
Sometimes. It gives the kitchen and the bedroom in one structure and costs less per square metre — but it almost always needs a planning application, where a single-storey extension plus a loft usually does not. Where the garden is short or the neighbours are close, the loft route wins. We compare both on the call.
Yes — a hip-to-gable loft conversion, a rear extension with an open-plan kitchen, a whole-house renovation, landscaping and a regulated outbuilding, all under one contract. It won the LABC Building Excellence Award 2024 for Best Residential Extension in London.
Where we build lofts and extensions together
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 combined projects: East Barnet EN4, Hendon NW4 and Fulham SW6.