Cost of Extension London Guide
At KT5 Construction, we understand that one of the biggest questions homeowners ask before starting a project is “What is the cost of extension in London?” Getting clear, accurate pricing is key to planning your dream home. This page will guide you through typical costs, what affects them, and how we can help you achieve your extension on budget and on time.
What We Do
Building Construction
New Builds, Extensions, Conversions, Renovations
General Building
Property Maintenance, Handyman Service, Decorating
Design
Planning, Design, Project Management, Quality Checking
Extension Costs in London
The cost of extension in London depends on the type, size, and finish. Here are average price ranges you can expect:
| Extension Type | Cost per m² | Typical Project Range |
|---|---|---|
| Single Storey Rear Extension | £1,800 – £2,800 | £36,000 – £112,000 |
| Double Storey Extension | £2,300 – £3,200 | £60,000 – £128,000 |
| Wraparound Extension | £2,500 – £3,500+ | £80,000 – £150,000+ |
| Side Return Extension | £2,000 – £2,900 | £40,000 – £80,000 |
| Loft Conversion | £1,600 – £2,500 | £30,000 – £80,000 |
These figures include labour, materials, and standard finishes. Premium materials, bespoke joinery, or complex structural changes may increase costs.
Factors That Influence the Cost of Extension in London
Every property is unique. The final cost will be shaped by:
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Size and Layout – Larger floorplans and complex designs cost more.
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Location – Central London projects tend to be higher due to labour and logistics.
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Materials and Finishes – Standard bricks and tiles are more affordable than premium stone or bespoke glazing.
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Planning or Permitted Development – Whether you need full planning permission will affect time and cost.
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Groundworks and Site Conditions – Access, drainage, and foundations can add to overall price.
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Labour and Professional Fees – Structural engineers, architects, and specialist trades are key parts of your budget.
Client Testimonials
“You made it so simple” – Just wanted to say thank you for making what I thought would be a difficult process much easier than I had imagined.
Thank you for my brand new house! The refurbishment and attention to detail makes it feel like a brand new house, but without the expensive cost of moving.
Just wanted to thank you for the work carried out to my new bathroom, I will definitely be in touch shortly to talk about my proposed kitchen extension.
Example Extension Cost in London
For a 12-metre rear extension, you can expect:
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Construction cost: £1,800 – £2,800 per m²
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Design and professional fees: £2,500 – £7,000
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Total build estimate: £60,000 – £120,000+
This range will vary depending on location, finish, and planning requirements.
How to Keep Extension Costs Under Control
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Choose simple layouts to avoid expensive structural changes.
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Use durable yet cost-efficient materials.
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Plan your design and finishes early to prevent mid-project changes.
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Work with a London builder who provides transparent pricing.
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Allow a 10–15% contingency for unexpected site conditions.
Why Choose KT5 Construction for Your London Extension
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Local Expertise – We know London borough planning rules and permitted development rights.
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Transparent Pricing – Clear, detailed quotations with no hidden costs.
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Design to Completion – From concept drawings to final finishes.
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Trusted Reputation – Proven track record of delivering extensions across London.
We make sure your extension not only meets your budget but also adds long-term value to your home.
Start Planning Your Extension Today
Understanding the cost of extension in London is the first step towards creating the space you need. At KT5 Construction, we guide you through every stage of the process with clarity and care.
Contact us today for a free consultation and transparent estimate tailored to your property.
Frequently Asked Questios
How much does a 20m² extension cost in London?
Between £36,000 – £56,000, depending on design and specification.
Can I build an extension for £50,000 in London?
Yes, for smaller single storey or side return projects, but larger or more complex designs will require a higher budget.
Do all extensions need planning permission?
Not always. Some projects fall under permitted development rights, but you should always check with your local authority or use a specialist builder.
Our Services
House Extensions
KT5 Construction provides professional house or Property Renovations Services in Ash, tailored to your unique needs. Whether you’re expanding your kitchen or creating an open-plan living area, we deliver high-quality results.
Kitchen Refurbishment
At KT5 Construction, we are specialists in kitchen refurbishment in Surrey and surrounding areas, delivering bespoke designs that enhance your living space and add value to your home.
Loft Conversions
At KT5 Construction, we specialise in creating stunning loft conversions in Surrey that add space, value, and style to your home. From dormer loft conversions to luxury loft designs, our expert team handles every detail with professionalism and precision.
Groundworks
At KT5 Construction, we pride ourselves on being the go-to groundwork Company in London, delivering top-quality services for residential and commercial projects.
Bathroom Design & Installation
Your bathroom should be more than just functional—it should reflect your personal style and offer a space to unwind. At KT5 Construction, we specialise in Surrey bathroom design and installation, delivering tailored solutions that blend elegance, practicality, and luxury.
Property Refurbishment
Our Ewell Road Surbiton Project showcases the full spectrum of our refurbishment expertise. By managing every detail, from architectural consultation to final finishes, KT5 ensures each element meets the highest standards.
New Build Homes
As a trusted New Build Builder in Surrey, KT5 Construction has been at the forefront of creating bespoke, high-quality homes designed to meet modern living standards.
Architecture & Design
Expert architectural planning & creative design solutions for residential and commercial projects in Surrey & London.
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