If you’re considering extending your home in London, one of the first questions is always:
“How much will it cost?”
In this 2026 guide, we break down realistic prices, what affects the cost, and what you should expect when planning a house extension in London.
Average House Extension Costs in London (2026)
The cost of a house extension depends on size, design, and specification, but here are typical price ranges:
Rear Extension
* £60,000 – £90,000
Ideal for expanding kitchens or creating open-plan living spaces.
Wrap Around Extension
* £80,000 – £120,000+
Combines side return + rear extension for maximum space.
Cost per m²
* £1,800 – £3,000 per m²
Lower end = basic finish
Higher end = premium finishes, glazing, steelwork, bespoke design
What Affects the Cost of a House Extension?
Several factors can significantly impact your final price:
1. Size and Design Complexity
* Larger extensions = higher cost
* Structural changes (steel beams, open plan) increase price
1. Ground Conditions & Foundations
* Poor soil or nearby trees may require deeper foundations
* Drainage relocation can add extra costs
1. Specification & Finishes
* Standard finish vs luxury materials
* Kitchen, flooring, glazing systems
This can change costs by £10,000–£30,000+
1. Planning & Structural Calculations
* Structural engineer: approx. £400–£1,000
* Planning drawings & approvals
1. Access to Property
* Limited access = higher labour costs
* Terraced houses often require more logistics
Real Example Project (London)
Here’s a typical rear extension project we completed:
Location: South London
Size: ~25m²
Cost Breakdown:
* Groundworks & foundations: £12,000
* Structure & brickwork: £18,000
* Roofing & insulation: £9,000
* Windows & doors (aluminium): £8,000
* Electrical & plumbing: £6,000
* Plastering & finishes: £7,000
Total: ~£60,000 + VAT
Timeline:
* Approx. 12–14 weeks
Is a House Extension Worth It?
In most cases — yes.
A well-built extension can:
* Increase property value by 15–25%
* Avoid the cost of moving
* Create modern, functional living space
Common Mistakes to Avoid
* Underestimating the budget
* Not including structural calculations
* Choosing cheapest builder instead of best value
* Poor planning of layout
Why Choose Constructum Code?
At Constructum Code, we provide:
* Full design & build service
* Transparent pricing
* High-quality workmanship
* Experience across London projects
Get Accurate Quote Within 24 Hours
Every project is different — the best way to understand your cost is a tailored estimate.
Get accurate quote within 24 hours
Send us:
* Your address
* Plans (if available)
* Photos of your property
We’ll provide a clear, realistic quote with no hidden costs.
Final Thoughts
House extension costs in London vary, but with the right planning and builder, you can achieve an excellent result within your budget.
If you’re considering extending your home in 2026, now is the perfect time to start planning.
