London's Loft Conversion & Extension Specialists
RCB Design & Build — Residential, Commercial, Bespoke. We specialise in loft conversions and house extensions across all London boroughs and the wider M25 area. Principal Contractor. Fixed price. Building Control managed.
60 years combined experience · 500+ London projects delivered · From Velux to mansard, from rear extensions to wraparounds
Our Two Core Specialisms
Everything else we do — bathrooms, kitchens, refurbishments, structural alterations — is associated work that comes as part of the loft conversion or extension. One team. One contract. One price.
Loft Conversions
Velux, rear dormer, hip-to-gable, L-shaped dormer and mansard. Most loft conversions are delivered under Permitted Development — no full planning required. Includes structural works, en-suite bathroom, staircase, insulation and first-fix M&E.
House Extensions
Rear extensions, side returns, wraparound extensions and double-storey additions. Planning and Building Control managed. Fixed price before we start. All associated works included — kitchen, utility, WC, steels, floor finishes.
Associated & Standalone Works
These services are most commonly delivered as part of a loft or extension project — but we also carry them out as standalone commissions.
Bathrooms & Ensuites
Almost every loft conversion includes an en-suite. Every extension includes a kitchen or utility. We do it all under one contract.
Kitchen Renovations
Full kitchen strip-out and fit — new layout, structural opening, plumbing, electrics and finishes. Part of the extension or standalone.
Full Refurbishments
First floor, ground floor or whole-house refurbishment alongside or separate from the main project.
Structural Alterations
Steel beams, RSJs, load-bearing wall removal. Structural engineer coordinated. Building Control managed.
HMO Conversions
Licensed HMO fit-out from 3–8 rooms. Fire compartmentation, emergency lighting, licensing compliance fully managed.
Garage Conversions
Integral or detached garage to habitable room. Planning, Building Regulations and fit-out under one price.
Who we work with
Our clients range from homeowners adding a bedroom to property developers managing large-scale conversions.
Homeowners
You want to add space without moving. We guide you from first conversation to Building Control sign-off.
Property Investors
Add value, maximise yield, convert HMOs. We understand the commercial logic of every decision.
Landlords
Refurbishments between tenancies, portfolio maintenance, HMO compliance. One contact for everything.
First-Time Buyers
Buying a property to improve? We give you a realistic picture of what it costs before you buy — or as soon as you do.
Property Developers
Design-and-build, principal contractor services, CDM management, full programme control.
Estate Agents & Brokers
Refer clients who need pre-sale renovation, extension potential advice or structural issue resolution.
What makes RCB different
Not the only builder in London. But one of the very few with this combination.
60 Years Combined Experience
Our site team includes tradespeople and project managers with decades of London residential and light commercial construction experience.
Loft & Extension Specialists
Not a general builder. Everything else we do — bathrooms, kitchens, refurbishments — is associated work that comes with the loft or extension.
Principal Contractor, Not a Subcontractor
RCB holds CDM principal contractor responsibility. You deal with one company, one contract, one fixed price.
M25 Coverage — All London + Surrounding Counties
We cover all London boroughs plus Essex, Surrey, Hertfordshire and Kent within the M25 and up to two hours' drive.
Fixed Price Before We Start
The price is agreed before the first tool is picked up. No extras unless you change the scope. Documented in writing.
Building Regulations, Planning & Structural — All Managed
We coordinate your architect, structural engineer, Planning Authority and Building Control. You don't have to chase anyone.
How it works — from enquiry to completion
A clear, staged process that protects your money and keeps the project on track.
Project review
We visit your property. No obligation, no cost. We assess what's possible and realistic.
Fixed-price estimate
After the survey and structural information, we issue a fully itemised fixed price in writing.
Planning & Building Control
We coordinate your architect, structural engineer, Planning Authority and Building Control.
Build & sign-off
We deliver on the programme. You receive a completion certificate and 25-year structural warranty.
What clients say
Checkatrade verified reviews — 9.96/10 from 114+ clients
“RCB converted our loft into a master bedroom and ensuite. The whole process was smooth from first visit to Building Control sign-off. They managed everything — we didn't have to chase anyone. Completed in 9 weeks, exactly as promised.”
“Our rear extension has completely transformed how we use the house. Fixed price meant no nasty surprises. Vasi and the team were professional throughout, kept us updated every week and the finish is excellent.”
“We had our HMO refitted to meet new licensing requirements. RCB knew exactly what Building Control needed — fire doors, emergency lighting, compartmentation — had it all done in under 8 weeks.”
“Hip-to-gable conversion with rear dormer. Very neat finish throughout — brickwork, internal plastering, the en-suite. They submitted the planning application and handled Building Regs sign-off themselves. Would recommend without hesitation.”
Everything you need to know before you build
Our knowledge hub covers planning permission, party wall agreements, types of drawings, Building Regulations, how to choose a builder, contractor insurance, JCT contracts, CDM duties, green energy and more. Free guides written by construction professionals.
Explore the knowledge hub →Free Resources & Downloads
Practical guides and templates you can use right now — no email signup required.
Party Wall Notice Template
A standard-form Party Wall Notice you can serve on your neighbour before starting work.
Download free →
How to Choose a Builder
10 questions to ask every builder before appointing. What insurance, what contract, what guarantees.
Download free →
Planning Application Checklist
What you need before submitting for planning permission or applying for a Lawful Development Certificate.
Download free →
Frequently asked questions
Straight answers to the questions we hear most.
What is the difference between Permitted Development and Planning Permission for a loft conversion?+
How long does a loft conversion take?+
What types of house extension are there?+
Do I need Building Regulations for a loft conversion?+
What is included in a loft conversion price?+
What is the difference between a principal contractor and a general builder?+
How do I know what my loft conversion will cost before I appoint anyone?+
Areas we cover
All London boroughs plus Essex, Surrey, Hertfordshire and Kent — within the M25 and up to two hours' drive.
Ready to add space? Let's start with a project review.
We visit your property, assess what's possible, and give you a realistic picture — at no cost and no obligation. We cover all of London and the surrounding counties.
Same-day response. Survey within the week. Fixed price before any work starts.