How Much Does a House Extension Cost in London in 2026?
- Amir Ijaz
- 5 minutes ago
- 7 min read
If you are planning to expand your living space, one of the first questions you will ask is: how much does a house extension cost in London in 2026? With rising property prices and limited space across the capital, many homeowners are choosing to extend instead of moving. A well-planned extension can add both comfort and long-term value but only if you understand the real costs involved.
The truth is that house extension cost in London varies widely depending on size, design, location, structural complexity, materials, and permissions. Online estimates often give rough figures, but they rarely explain what is actually included or what hidden costs may appear later.
This in-depth guide breaks down London house extension costs, cost per square metre, extension types, labour and material pricing, planning factors, and ways to control your budget. Whether you are considering a rear extension, side return, kitchen extension, or double storey build, this article will help you plan with confidence.
Why More London Homeowners Are Choosing Extensions in 2026?
Moving house in London has become increasingly expensive. Stamp duty, legal fees, agent commissions, and relocation costs can easily exceed the price of extending your current property. That is why demand for home extensions in London continues to grow.
Homeowners are extending to:
Add larger kitchens and dining areas
Create home offices
Build extra bedrooms
Increase property value
Avoid moving costs
Improve layout and functionality
A professionally built extension by experienced house extension builders in London can significantly improve both lifestyle and resale potential but cost planning is critical from day one.
Average House Extension Cost in London in 2026
Let’s start with a realistic overview.
In 2026, the average house extension cost in London typically ranges between:
£2,500 – £4,500 per square metre
This range depends on build quality and specification level.
Typical Total Project Ranges
Extension Size | Estimated Cost Range London |
20 m² | £50,000 – £90,000 |
30 m² | £75,000 – £135,000 |
40 m² | £100,000 – £180,000 |
50 m² | £125,000 – £225,000 |
These figures reflect mid-range to good quality construction by a reliable construction company in London, not budget shortcuts or ultra-luxury finishes.
Extension Cost Per Square Metre in London
The most common pricing method used by extension builders London is cost per square metre.
Cost Per sqm by Specification
Build Level | Cost per sqm London |
Basic finish | £2,500 – £3,000 |
Mid-range finish | £3,000 – £3,800 |
High-end finish | £3,800 – £4,500+ |
What Changes the Cost per sqm?
Structural complexity
Ground conditions
Steel beam requirements
Glass features
Kitchen/bathroom installations
Bespoke joinery
Underfloor heating
Smart home systems
House Extension Cost by Extension Type
Different extension styles carry different construction costs. Let’s break them down.
Rear House Extension Cost London
Rear extensions are the most popular option.
Average cost: £60,000 – £140,000+
Rear extensions often include kitchen extensions and open-plan living spaces. Costs rise when large glazing, bifold doors, or structural wall removals are involved.
Side Return Extension Cost London
Common in terraced and semi-detached homes.
Average cost: £45,000 – £110,000
These projects often involve tight access and drainage adjustments, which can increase labour complexity.
Wrap Around Extension Cost London
Combines rear + side extension.
Average cost: £95,000 – £200,000+
More structural work, more steel, more roofing complexity but delivers dramatic layout improvements.
Single Storey Extension Cost London
Average cost: £2,500 – £4,000 per sqm
Most kitchen and living space extensions fall into this category.
Double Storey Extension Cost London
Average cost: £3,200 – £4,800 per sqm
Higher upfront cost but better value per square metre long term because foundations and roofing are shared across two floors.
Kitchen Extension Cost London
Kitchen extensions are among the most searched topics in home extension cost UK London queries.
Typical Kitchen Extension Budget
Level | Cost |
Build only | £45,000 – £85,000 |
With mid-range kitchen | £70,000 – £120,000 |
High-end kitchen fit | £110,000 – £180,000 |
Kitchen installation, appliances, ventilation, and plumbing significantly affect final price.
Labour Cost for Extension in London
Labour is a major component of building extension cost London.
Typical Labour Share
Labour usually represents 35% – 50% of the total project cost.
Skilled trades involved:
Builders
Bricklayers
Electricians
Plumbers
Roofers
Plasterers
Carpenters
Tilers
Experienced construction contractors London charge more but reduce costly mistakes and rework.
Material Cost for House Extensions
Material prices fluctuate yearly. In London projects, material cost typically accounts for:
30% – 40% of total extension cost
Includes:
Bricks and blocks
Steel beams
Concrete
Timber
Insulation
Roofing systems
Windows and doors
Premium materials raise costs but improve durability and energy efficiency.
Planning Permission and Building Regulation Costs
Many homeowners ask: Do I need planning permission for extension London?
Some extensions fall under permitted development, but not all.
Typical Permission & Compliance Costs
Item | Estimated Cost |
Planning drawings | £1,200 – £3,000 |
Planning application | £250 – £350 |
Building control | £700 – £1,500 |
Structural engineer | £800 – £2,500 |
Reliable home extension contractors London usually guide clients through this process.
Architect and Design Fees
Professional design improves both usability and approval chances.
Architect fees: 5% – 10% of build cost or fixed packages £2,000 – £6,000+
Design fees vary by complexity and service level.
Hidden Costs of House Extensions in London
Many budgets fail because hidden costs were ignored.
Commonly Missed Costs
Party wall agreements
Drain relocation
Ground reinforcement
Asbestos surveys
Utility upgrades
Temporary accommodation
Site access equipment
This is why experienced extension builders North West London recommend a contingency budget of 10–15%.
House Extension Cost North West London vs Central London
Location affects price.
Cost Differences
Central London: Higher labour + logistics cost
North West London: More moderate contractor rates
Tight access areas: Extra handling cost
House extension cost North West London is often 5–12% lower than central zones — depending on access and borough regulations.
How Long Does a House Extension Take?
Time affects cost through labour and site overheads.
Typical Timelines
Extension Type | Duration |
Small | 8–12 weeks |
Medium | 12–16 weeks |
Large | 16–24+ weeks |
Delays increase cost — proper construction project management London reduces this risk.
Does an Extension Add Value to London Property?
In many cases yes.
Well-designed extensions can add:
10% – 25% property value uplift
Best ROI areas:
Kitchen extensions
Open plan living
Extra bedrooms
Double storey extensions
Is It Cheaper to Extend or Move in London?
For many households extending is cheaper.
Moving costs often include:
Stamp duty
Legal fees
Surveys
Agent fees
Removal costs
These alone can exceed £40,000–£80,000 before buying a larger property.
How to Reduce House Extension Cost Without Sacrificing Quality
Smart planning helps control extension construction costs in London.
Practical Cost Control Tips
Finalise design early
Avoid mid-build changes
Use standard material sizes
Choose mid-range finishes
Work with experienced builders
Get detailed written quotes
Plan utilities carefully
How to Get an Accurate House Extension Quote in London
Always request a fully itemised quotation.
A professional construction company London should include:
Scope of work
Material specs
Labour breakdown
Timeline
Payment schedule
Exclusions list
Never rely on verbal estimates.
Choosing the Right House Extension Builders in London
Cost matters but reliability matters more.
Choose builders who offer:
Proven extension portfolio
Insurance and certifications
Transparent pricing
Clear communication
London project experience
Final Thoughts: Plan Smart, Build Once
Understanding the house extension cost in London in 2026 helps you plan realistically and avoid financial surprises. Extensions are major investments but when designed and built properly, they transform both lifestyle and property value.
Every project is unique. Size, design, permissions, materials, and contractor quality all influence the final figure. That is why personalised quotations from experienced professionals are essential.
Get a Professional Extension Cost Estimate
If you are planning a rear extension, side return, kitchen extension, or double storey build, speaking with an experienced London construction team can save you time and money.
NILO Construction provides expert house extension services across London and North West London from design support and permissions to full construction and project management.
👉 Request your free extension consultation and cost estimate today and get expert guidance tailored to your property and budget.
Build smarter. Extend with confidence.
Frequently Asked Questions House Extension Cost in London
How much does a typical house extension cost in London in 2026?
The typical house extension cost in London in 2026 ranges from £2,500 to £4,500 per square metre, depending on the design, build quality, materials, and structural requirements. A small single storey extension may cost around £60,000, while larger or high-spec extensions can exceed £150,000.
How much does a 3-metre house extension cost in London?
A standard 3-metre rear house extension in London usually costs between £45,000 and £90,000+. The final price depends on property width, glazing choices, kitchen installations, and whether structural steelwork is required.
Is it cheaper to extend a house or move in London?
In many cases, extending is cheaper than moving. When you factor in stamp duty, legal fees, estate agent charges, and removal costs, moving to a larger property in London can cost more than building a well-planned extension — especially if you already like your location.
Do I need planning permission for a house extension in
London?
Not always. Many house extensions fall under permitted development rights, meaning full planning permission is not required. However, size limits, property type, and borough rules apply. It is always best to confirm with your local council or a professional construction company in London before starting work.
How long does a house extension take to build in London?
Most house extensions in London take between 10 and 20 weeks to complete. Smaller projects may finish sooner, while larger or more complex extensions such as wrap-around or double storey builds can take longer.
Does a house extension add value to a London property?
Yes, a well-designed and professionally built extension can add 10% to 25% to your property value in London. Kitchen extensions, additional bedrooms, and open-plan living spaces usually deliver the strongest return on investment.
How can I reduce my house extension cost without lowering the quality?
You can control house extension costs by finalising the design early, avoiding mid-project changes, choosing practical materials, and working with experienced extension builders in London who provide detailed written quotations and proper project planning.
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