What is the Average Cost of a Side Extension in London?
At KT5 Construction, we know that one of the most common questions homeowners ask before starting a project is: “What is the cost of side extension London?” Understanding costs clearly at the beginning helps you plan with confidence and avoid unexpected surprises.
This page will guide you through the typical costs for side return and side extensions in London, the factors that influence pricing, and how our expert team ensures your project is delivered 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
Cost of Side Extension in London
The cost of side extension London varies depending on design, size, and finish. On average, you can expect:
| Extension Type | Cost per m² | Typical Project Range |
|---|---|---|
| Side Return Extension | £2,000 – £2,900 | £40,000 – £80,000 |
| Single Storey Extension | £1,800 – £2,800 | £36,000 – £112,000 |
| Double Storey Extension | £2,300 – £3,200 | £60,000 – £128,000 |
These figures include labour, materials, and standard finishes. If you opt for premium glazing, bespoke joinery, or more complex structures, the cost of side extension London may increase.
Factors That Affect the Cost of Side Extension London
Every property is different, and your final budget will depend on several factors:
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Size and Layout – A larger side return with complex layouts costs more.
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Location – Central London side extensions are often higher due to labour and logistics.
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Materials and Finishes – Choosing premium stone, steel, or bespoke glazing can raise prices.
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Planning and Permissions – Whether your extension falls under permitted development or requires planning will affect cost and time.
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Groundworks – Drainage, foundations, and access restrictions can add to the cost of side extension London.
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Professional Fees – Structural engineers, architects, and specialists are part 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.
How to Manage the Cost of Side Extension London
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Keep designs simple to avoid unnecessary structural changes.
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Select durable but cost-efficient materials.
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Confirm finishes and layouts early to prevent expensive variations.
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Work with KT5 Construction for transparent and detailed costings.
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Allow 10–15% contingency for unforeseen site conditions.
Why Choose KT5 Construction
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Local Knowledge – We understand borough planning requirements across London.
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Transparent Pricing – Clear, detailed quotations with no hidden extras.
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Design to Completion – From concept drawings through to final finishes.
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Proven Track Record – Delivering extensions that add space and long-term value.
We ensure your side extension not only meets your budget but also enhances your home.
Start Planning Your Side Extension Today
Understanding the cost of side extension London is the first step in creating the extra space your family needs. At KT5 Construction, we provide clear estimates and a smooth process from start to finish.
Review our Cost of Extension London Guide for more detail and get in touch with us today for a tailored quotation.
Contact Us to book your free consultation.
Frequently Asked Questios
How much does a side extension cost in London?
Between £40,000 – £80,000, depending on size, location, and specification.
Can I build a side return extension for £50,000 in London?
Yes, depending on design simplicity, materials chosen, and site conditions.
Do all side extensions need planning permission?
Not always. Some side extensions fall under permitted development, but rules vary by borough.
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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