Design and build services across London and Hertfordshire

LCCL Construction is a design and build company based in Finchley N3. Since 2004 we have designed and built loft conversions, house extensions, renovations, basements and new homes across London and Hertfordshire, under one contract with one point of contact from the first sketch to handover. We are LABC Building Excellence Award winners (Best Residential Extension in London 2024, and 2026 London regional winner for Best Conversion or Alteration to an Existing Home), members of the National Federation of Builders and LABC Registered Partners.

Every figure below is a 2026 London design-and-build range from our master price list. Each home is surveyed and costed individually and you receive a detailed itemised estimate — the figure on that estimate is the figure you pay, nothing is added afterwards. Not sure where to start? Get an instant estimate for your postcode or book a free 30-minute call.

Loft conversions

Velux, rear dormer, L-shaped, hip-to-gable and mansard conversions, from £27,000 for a rooflight loft to £64,000–£124,000 for a mansard. Most semi-detached and terraced lofts fall under permitted development; we handle the drawings, structural calculations, building regulations, fire safety and the build. Loft conversions · Compare the types · Loft conversion cost

House extensions

Rear, side return, wraparound, kitchen, ground floor and two-storey extensions. A single-storey rear extension runs £35,000–£75,000, a side return £35,000–£78,000, a wraparound £60,000–£128,000 and a two-storey extension £75,000–£165,000. House extensions · Extension types · House extension cost

Home renovation

Kitchen renovations, flat refurbishments and whole-house renovations, including the layout changes, structural openings and finishes that turn several rooms into one plan. Our Weech Road NW6 penthouse renovation won the LABC 2026 London regional award. Home renovation

Basement conversions

Cellar refits (£45,000–£95,000), floor lowering (£95,000–£180,000) and new basement digs (£180,000–£300,000+), with waterproofing design and structural engineering included. Basement conversions

New build homes

New houses from £250,000 (£2,200–£4,500 per m²), from feasibility and planning through to completion and warranty. New build construction

Design and build

One contract covers the survey, drawings, planning application, structural calculations, building regulations, party wall notices and the build itself. Architects, structural engineers and specialist trades are coordinated by our team so you deal with one person throughout. How design and build works · How a project runs

Professional services on their own

If you only need the paperwork, we also offer these as standalone services: architectural design and planning drawings (from £750), structural calculations (£450–£8,000), measured building surveys, party wall matters, planning permission, building regulations and project management.

Where we work

Finchley, Barnet, Hendon, Mill Hill, Muswell Hill, Hampstead and the rest of North and North West London are on our doorstep; we also build across Central, West, South West, East and South East London and in Hertfordshire (Borehamwood, Potters Bar, St Albans, Watford). All areas

Frequently asked questions

What does a design and build contract include?
Survey, drawings, planning and building regulations applications, structural calculations, party wall notices, the construction itself and the completion certificate, all under one contract and one point of contact.

Do you work under permitted development?
Wherever the rules allow. Most rear dormers, hip-to-gable lofts and single-storey rear extensions on houses fall under permitted development; we apply for a lawful development certificate so you have proof. Flats, conservation areas and larger schemes need a planning application, which we prepare and submit.

What warranty do you give?
Twelve months on finishes and decoration from LCCL, plus a 10-year LABC structural warranty if you sign up to it, issued once the final invoice is paid.

How are payments structured?
A booking fee, then staged payments as per contract, each sized to the contract value.

What is the first step?
A free 30-minute phone call with our team. Call 020 8037 7332 or book a time online; if you would rather see a figure first, the instant estimate takes two minutes.