Design & build · London and Hertfordshire
Extensions, loft conversions and new builds — designed, built and guaranteed by one team.
Architects, structural engineers and project managers, all under one contract and one point of contact — from first sketch to handover. LABC Building Excellence Award winners 2024 and 2026.
What will it cost?
Full postcode and project for a quick range. Size, finish and drawings on the full estimator.
Enter your full postcode
Priced for your area — type your full postcode, e.g. N3 1QF
Estimated costs, not fixed prices. Ranges include architecture, structural calculations, building regulations, construction and finishing. Final figure follows drawings and a site visit.
LABC Award winners 2024 and 2026
Building Excellence Awards 2024 & 2026, London
Since 2004
Design & build from Finchley N3, London & Hertfordshire
4.7/5 · 200+ reviews
Google, Trustpilot, Houzz, Yell and Reviews.io
One contract
Design, approvals and build under one agreement
LABC Registered Partner
Full-plans approval and inspections through LABC
NFB member
National Federation of Builders — vetted member
Dormer, hip-to-gable, L-shaped and mansard lofts — a bedroom and bathroom without moving house.
FROM £47,000 · DORMER, DESIGN & BUILD
Rear, side return, wraparound and two-storey extensions, designed around how you cook, eat and live.
FROM £35,000 · REAR OR SIDE RETURN
Whole-house refurbishment and reconfiguration, often combined with an extension or loft in one programme.
PRICED FROM A MEASURED SURVEY
New homes, infill plots and garden houses — from planning to the completion certificate.
£2,200–£4,500 PER M² · DESIGN & BUILD
Cellar refits, lowering and new digs for the space you cannot add above ground.
FROM £45,000 · CELLAR REFIT
Architecture, structural calculations, planning applications, building regulations and party wall — by the team that builds it.
INCLUDED IN EVERY DESIGN & BUILD PROJECT
Why homeowners choose LCCL
The people who draw your project are the people who build it
No hand-off between an architect who has never built and a builder who has never designed, no gap in responsibility when the steel arrives, and one person answerable for the drawings, the approvals, the build and the certificate at the end.
Survey, drawings, planning, structural calculations, building regulations, party wall, construction and guarantees in one agreement with one company — an NFB member and LABC Registered Partner.
Every project is priced from a measured survey, line by line — design, planning, structure, construction and warranty. No allowances that grow later.
Nothing starts on site until planning, LABC full-plans approval and the party wall notices are signed off.
One project manager from the first sketch to handover, with a weekly progress update in writing.
A free 30-minute phone call with our team, no obligation.
Awards and accreditations
LABC Building Excellence Award winners, 2024 and 2026
The LABC awards are judged by Local Authority Building Control officers — the inspectors who check and sign off building work — on quality, compliance and craftsmanship. Two wins in three years.
2024 · Best Residential Extension in London
Hip-to-gable loft, full-width rear extension, two new bathrooms, whole-house renovation and landscaping — about 1,000 sq ft added. Read the case study →
2026 · London Regional Winner, Best Conversion or Alteration to an Existing Home
Top-floor flat converted into a penthouse duplex: kitchen and living space in the new loft, two bathrooms, an extra bedroom. Through to the national Grand Finals, January 2027. Read the case study →
Membership
Independent vetting on joining and ongoing compliance with the NFB's professional standards — a membership you can check, not a badge we awarded ourselves. What our memberships mean →
Building control
Our building-regulations drawings and structural calculations are checked by LABC before work starts; inspections at every stage and the completion certificate at handover. Best of Houzz Service 2020–2026.
WEEK 0
Free consultation call
A 30-minute phone call about the house, what you want from the space and a realistic budget. Your instant estimate is the starting point.
WEEKS 1–4
Survey & design
Measured survey, architectural drawings and your detailed itemised estimate — priced line by line.
WEEKS 4–12
Approvals
Lawful Development Certificate or planning application, building-regulations drawings, structural calculations, party wall notices.
BUILD
On-site
4–24 weeks for most projects, with LABC inspections at every stage and a weekly update from your project manager.
HANDOVER
Sign-off
Snagging, LABC final inspection and completion certificate, guarantees in writing. 10-year LABC Warranty available.
Penthouse duplex loft conversion and renovation.
LABC 2026 London winner · +800 sq ft · 18 weeks on site
Rear extension, hip-to-gable loft and full renovation.
LABC 2024 London winner · +1,000 sq ft · 30 weeks on site
3,033 sq ft new build family home, one team throughout.
New build · completed 2026 · 60 weeks on site
3 × 10 m kitchen extension, finished two weeks early.
Kitchen extension · +500 sq ft · 10 weeks on site
ANDERSON · FOUNDER, LCCL CONSTRUCTION
Use the winter for the paperwork, build in spring
Approvals are the part of the programme you cannot compress. Design and planning typically take 8–16 weeks, and the party wall notices on a semi can add up to three months on top. Start the survey and drawings this autumn and you go through the council queue over winter, with everything signed off for a start on site in early spring — the slot most families want and the one that goes first.
August is our slowest month for project starts; the families who begin their design in autumn are the ones on site before the summer holidays.
“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
“Rear house extension 6x3m and dormer loft conversion completed with LCCL Construction, finished the whole project in 14 weeks very happy with the outcome, highly skilled and experienced design and build company a perfect match for our house. Would highly…”
Fran S · Reviews.io
“Total refurbishment and side return extension in East Finchley. LCCL totally refurbished our 3-bed Victorian terraced house in East Finchley and built a new 5m side return extension. This means rewiring, re-plumbing, drainage, sewer, and waste. Building a…”
A Davidsson · Google Reviews
£35,000 – £75,000
Single-storey, design and build inclusive, to plaster finish with first-fix electrics and plumbing.
Rear extension cost
£47,000 – £67,000
Rear dormer with a bedroom and en-suite; usually permitted development.
Loft conversion cost
£60,000 – £128,000
Side return and rear combined for the biggest ground floor a terrace can take.
Wraparound cost
Every project is priced from your postcode and house type: Inner London adds 10–15%, Central London 20–25%, Hertfordshire is about 5% less. Kitchen fit-out, flooring and second-fix items you choose are on top. The figure on your itemised estimate is the figure you pay — nothing is added afterwards. Every extension type priced →
Where we work
Finchley N3 outwards London and Hertfordshire
Most of our extensions and lofts are within 45 minutes of the office, so Anderson can be on site when it matters. Recent projects: Hampstead NW6, East Barnet EN4, Hadley Wood EN4, Mill Hill NW7, Finchley N3, Putney SW15, Wood Green N22 and Borehamwood WD6. Planning rules by council → — every London and Hertfordshire council's extension and loft rules on one page.
Questions we're asked most
Before you book a call
Usually not for a single-storey rear or side return extension or a rear dormer loft — they are permitted development and we obtain a Lawful Development Certificate. Wraparounds, two-storey extensions, mansards, flats and conservation-area houses need a full application with an eight-week decision. We check your address before the first drawing.
Typically 8–16 weeks of design and approvals, then 4–24 weeks on site depending on the project — a rear extension is on site 10–14 weeks, a loft 4–16, a two-storey extension 18–26, a new build 30–50.
Yes. On a terrace or semi nearly every extension and loft needs notices to the adjoining owners, two months before the work (one month for excavation). We serve the notices and manage the process; most neighbours consent, and a surveyor is only needed if one dissents.
A booking fee on signing reserves your start window. The build is then paid in stages set out in the Schedule of Works: each stage is invoiced when the previous one is complete and paid, by bank transfer, before that stage starts. The stage sums are fixed in the signed schedule.
From Finchley N3 we cover North, North-West, Central, South-West and West London and Hertfordshire, and we also work across the rest of London, Buckinghamshire, Surrey, Kent and Essex. The instant estimate adjusts the range for your postcode.
Latest guides
Costs, planning and how a project runs
When structural calculations are needed, typical costs, what is included and who does them.
25 Aug 2026 · 3 min read
Costs, loft types, planning rules and the Hampstead NW6 penthouse duplex loft conversion case study.
25 Aug 2026 · 3 min read
Costs, design, planning and the Bohun Grove EN4 East Barnet full renovation case study.
25 Aug 2026 · 3 min read
Costs, timelines, planning and the Hadley Wood EN4 new build family home case study.
25 Aug 2026 · 3 min read