Double Storey Extension Cost in London: Complete 2026 Guide
A double storey extension is one of the most effective ways to increase your home’s living space without the expense and disruption of moving. With property prices across London continuing to rise, many homeowners are choosing to extend rather than relocate, creating larger homes that better suit their family’s needs while adding significant value to their property.
Whether you’re planning additional bedrooms, a larger kitchen, a home office, or an open-plan living area, understanding the costs involved is essential before starting your project.
In this guide, we’ll explain the average cost of a double storey extension in London, the factors that influence pricing, financing options, and how to maximise your investment.
What Affects the Cost of a Double Storey Extension?
No two extension projects are the same. The final price depends on several factors, including the size of the extension, the complexity of the design, material choices, and labour costs.
1. Size of the Extension
The size of your extension is the biggest factor affecting the overall cost.
A larger extension requires:
- More building materials
- Additional labour
- Larger foundations
- More structural steel
- Increased roofing and insulation
For example, adding two bedrooms above an existing extension will generally cost less than creating a large open-plan kitchen-diner with multiple bathrooms and bespoke finishes.
Although larger extensions require a higher upfront investment, they often deliver greater increases in property value.
2. Quality of Materials
The materials you choose can significantly influence both the cost and long-term performance of your extension.
Higher-quality materials typically offer:
- Better energy efficiency
- Improved durability
- Reduced maintenance
- Longer lifespan
- Enhanced appearance
Examples include:
- Premium brickwork
- Triple-glazed windows
- Natural stone flooring
- Hardwood doors
- Slate roofing
- High-performance insulation
While premium materials increase initial costs, they often provide better value over the lifetime of your home.
3. Design and Architectural Features
The complexity of your extension design plays a major role in determining the overall budget.
Features that commonly increase costs include:
Roof Design
A pitched roof generally costs more than a flat roof because it requires additional timber, insulation, roofing materials, and labour.
Windows and Doors
Large glazed areas, bi-fold doors, roof lanterns, and bespoke windows can significantly increase costs while improving natural light and aesthetics.
Exterior Finishes
Your choice of external finish can affect both price and appearance, including:
- Brickwork
- Render
- Timber cladding
- Stone finishes
Matching existing materials often produces the best visual results.
Interior Finishes
Internal specifications can vary dramatically depending on your budget.
These include:
- Flooring
- Kitchens
- Bathrooms
- Lighting
- Built-in storage
- Decoration
Luxury finishes naturally increase the overall project cost.
Additional Rooms
Adding specialist rooms such as:
- Bathrooms
- Utility rooms
- Home offices
- Kitchens
requires extra plumbing, electrical work, ventilation, and specialist trades.
Planning Permission and Building Regulations
Many homeowners assume every extension requires planning permission, but that’s not always the case.
Some double storey extensions may fall within Permitted Development Rights, although many larger projects still require planning approval.
Factors affecting permission include:
- Extension size
- Property location
- Conservation areas
- Green Belt restrictions
- Listed building status
Regardless of planning permission, every extension must comply with Building Regulations covering:
- Structural integrity
- Fire safety
- Insulation
- Ventilation
- Drainage
- Energy efficiency
Professional architectural drawings and structural calculations are usually required.
Labour Costs
Labour represents one of the largest portions of your extension budget.
Typical trades involved include:
- Builders
- Bricklayers
- Roofers
- Carpenters
- Electricians
- Plumbers
- Plasterers
- Decorators
Labour costs in London are typically higher than elsewhere in the UK due to increased demand and the higher cost of living.
Projects involving complex structural alterations, restricted site access, or heritage properties will usually require more experienced tradespeople, increasing costs further.
Average Double Storey Extension Cost in London
The cost of a double storey extension depends on the specification and complexity of the project.
As a general guide:
| Extension Size | Estimated Cost |
|---|---|
| Small Extension | £50,000–£75,000 |
| Medium Extension | £75,000–£110,000 |
| Large Extension | £110,000–£150,000+ |
These estimates typically include structural work, roofing, windows, insulation, and standard internal finishes.
Additional costs may include:
- Architectural drawings
- Structural engineering
- Planning applications
- Building Control fees
- Party Wall Agreements
- Landscaping
- Interior furnishing
Obtaining several detailed quotations is the best way to understand the likely cost of your project.
How to Finance a Double Storey Extension
A double storey extension is a significant investment, but there are several financing options available.
Popular choices include:
- Home improvement loans
- Further advances on your mortgage
- Remortgaging
- Personal loans
- Savings
- Homeowner finance packages
Before borrowing, consider the likely increase in your property’s value. A well-designed extension can often provide an excellent return on investment while improving your quality of life.
Double Storey Extension Before and After
One of the biggest advantages of a double storey extension is the complete transformation it can bring to your home.
Typical improvements include:
- Larger open-plan kitchens
- Additional bedrooms
- Extra bathrooms
- Dedicated home offices
- Utility rooms
- Family living spaces
- Improved natural light
- Better property layout
The result is a home that feels significantly larger, more modern, and better suited to your lifestyle without the need to move.
Why Choose Powerpillar for Your Double Storey Extension?
Choosing the right contractor is just as important as choosing the right design.
Powerpillar provides professional double storey extension services across East London and Essex, delivering high-quality workmanship from concept through to completion.
Our experienced team can assist with:
- Initial design consultations
- Planning applications
- Structural calculations
- Building Regulations
- Full project management
- Construction and finishing
We work closely with homeowners to ensure every extension is completed safely, efficiently, and to the highest standards.
Is a Double Storey Extension Worth It?
For many London homeowners, a double storey extension offers better value than moving house.
Benefits include:
- Increased living space
- Higher property value
- Improved functionality
- Better use of existing land
- Avoiding moving costs
- Customised layouts to suit your family
When carefully planned and professionally built, a double storey extension can become one of the most valuable investments you make in your home.
Final Thoughts
A double storey extension is an excellent way to create additional living space while increasing the value of your property. Although costs vary depending on size, materials, design, and labour, careful planning and realistic budgeting can help you achieve the best results.
Working with experienced architects, structural engineers, and reputable builders will ensure your extension complies with regulations and is completed to a high standard.
If you’re considering extending your London home, obtaining professional advice and detailed quotations is the first step towards creating a larger, more functional home that meets your family’s needs for years to come.
