London extension specialists
Design, planning and build, handled end to end. Beautiful extensions, lofts and whole-house transformations across London, with deep roots in the capital's finest streets.
Professional home extension for every project
Residential extensions, renovations, and new home designs tailored to your vision
Conservation areas, wealth-belt streets and characterful stock — sensitive design that wins approval
Expert guidance through extension planning permission, extension building control, and permitted development
Get your extension project completed in 3 simple steps
Tell us about your project vision and requirements through our simple online form
Our house extension specialists create detailed designs and handle all extension planning applications
Complete your extension project with professional drawings and approvals
What clients say
“Used The Extension Company for a loft conversion on our semi detached in Barnet and couldn't be happier. They explained what was possible at the first visit, sorted the planning side, and gave a fixed price with no surprises at the end.…” read the full review
“Really impressed with the entire project. The side extension and conservatory have been finished to a very high standard and the team made the process straight forward and stress-free. It’s transformed the space and added so much value, would definitely recommend.”
“Brilliant experience with the extension company, transparent from the word go. Completed a double story extension for me and I couldn’t be more pleased. Thank you”
“I got the extension company to do a bathroom refurb for us a January they done a great job they managed to fit in a large shower as well as a bath”
Reviews shown word for word from our Google profile. Read all 8 reviews on Google
Professional house extension specialists across London
Quick design decisions and efficient project delivery. No delays, no excuses.
Transparent fees and competitive pricing. No hidden charges.
Dedicated house extension specialists guide you through every step of the design process.
Experienced team with strong track record of extension planning application approvals.
Consistent success in getting extension planning applications approved across London and Hertfordshire.
Residential, commercial, extensions, renovations - we design it all.
Professional house extension services for every need
Professional single storey extension design and planning for ground floor expansions
Two-storey home extension design maximizing space and value
Garden-facing extensions creating seamless indoor-outdoor living
Narrow extensions utilizing side garden space efficiently
Specialized kitchen and dining space extensions for modern living
Converting attic space into valuable living areas
Underground extensions creating additional living space
Expert guidance through planning applications and permitted development
Comprehensive extensions combining rear and side elements for maximum space
Comprehensive whole-house renovation and modernization services
Expert structural engineering services including underpinning and load-bearing work
Converting garages into functional living spaces for bedrooms, offices, and studios
Where we work
Forty area guides built on real council planning data — from our Cockfosters base across Enfield, Barnet and the Hertfordshire border. And we now build south of the river too.
Get answers to common home extension questions
A single-storey rear extension typically runs £60,000 to £120,000+ in North London depending on size, glazing and finish. We quote a fixed, itemised figure after a free site visit — or design yours in the Extension Builder for an honest guide price in 60 seconds.
Many single-storey extensions fall under permitted development, so no full application is needed. Where permission is required, we design to what your council demonstrably approves and handle the whole application for you.
Design and planning usually take 8-12 weeks, and a single-storey build typically 10-16 weeks on site. We agree a programme with you before work starts and manage it end to end.
The Extension Company is the extensions studio of Pine Grove Design & Build Ltd — the same team designs, manages and builds your project. Nothing is passed on, sold on, or subcontracted to strangers.
Yes. You get a fixed, itemised figure before you sign, and the number you sign is the number you pay — it only changes if you change the specification.
Everything: design and drawings, the planning application, building control, structural engineering, the build itself and project management — one team from first sketch to handover.
Most London extensions touch a shared wall, so yes — we advise on party wall notices early and work alongside appointed surveyors so the agreement never holds up your build.
All our designs comply with UK building regulations, and we produce the technical drawings and manage building control sign-off as part of the fixed price.
Yes — loft conversions, wrap-arounds, double-storey extensions and whole-house transformations across North London and the Hertfordshire border.
We can usually do your free site visit within days, design starts straight after, and build slots are typically booked 6-10 weeks out. Call 020 3051 9430 to check current lead times.
Have more questions? Get personalized answers below.
Get a QuoteTell us about your needs and get a personalized quote in minutes
Practical advice on costs, planning permission, and design from our house extension specialists.
A loft extension is a loft conversion that grows the roof — dormer, hip-to-gable or mansard. 2026 North London costs, the 40m³/50m³ rules, and when planning is needed.
Read Guide
A self-contained granny annexe almost always needs planning permission — the garden-building PD shortcut rarely applies. The 2026 rules on ancillary use, kitchens, two-storey annexes, council tax and honest North London costs.
Read Guide
Yes — a garden room costs roughly half as much per square metre as an extension. But only one adds floor area to your house. The honest 2026 money comparison.
Read GuideGet answers to the most common questions about home extension
Our expert team is here to help you with your home extension needs
Discover our comprehensive range of house extension solutions across North & South London
Call now to speak with our expert team. Get instant responses and professional guidance for your extension project.