House extensions are one of the most searched home renovation topics in the UK, and demand is even stronger in London. With rising property prices, limited space, and high moving costs, many homeowners now choose to extend their existing homes rather than relocate.
At London Renovations, house extensions are a core service, helping homeowners unlock additional space, improve layout, and significantly increase property value. This guide explains house extension costs in London, the main factors that affect pricing, planning rules, timelines, and whether an extension is worth the investment in 2026.
Average House Extension Costs in London
Extension costs in London are typically 20–30% higher than the UK average. This is mainly due to skilled labour demand, access challenges, structural complexity, and stricter planning conditions in many boroughs.
Typical London Extension Costs (2026)
- Single-storey extension: £1,900 – £2,800 per m²
- Double-storey extension: £2,200 – £3,200 per m²
- Side return extension: £45,000 – £85,000
- Rear extension: £60,000 – £120,000+
- Wraparound extension: £90,000 – £160,000+
These figures include structural work, basic finishes, and standard compliance but may vary depending on design complexity and specification level.
London Renovations provides detailed, itemised quotations so clients have full cost clarity before work begins.
What Factors Affect House Extension Costs?
No two extensions cost the same. Several key factors determine the final budget.
Structural Requirements
Steel beams, foundation depth, ground conditions, and load-bearing alterations significantly impact costs. Older London properties often require additional structural reinforcement.
Property Type
Terraced, semi-detached, detached, and listed buildings all present different challenges. Period homes may require specialist construction methods and heritage-sensitive design.
Access & Logistics
Restricted access, narrow streets, parking limitations, and material handling in London can increase labour time and overall costs.
Materials & Glazing
High-quality finishes such as bi-fold doors, sliding glazing systems, roof lanterns, and energy-efficient windows enhance value but add to the budget.
Professional Fees
Architects, structural engineers, building control, and party wall surveyors typically account for 8–15% of the total project cost. These services are essential for safety, compliance, and long-term performance.
Planning Permission & Building Regulations in London
Many house extensions fall under permitted development rights, meaning planning permission may not be required. However, permission is needed when:
- Size or height limits are exceeded
- The property is listed
- The home is in a conservation area
- The extension affects neighbouring properties
Regardless of planning permission, Building Regulations approval is always mandatory. This covers structural integrity, insulation, fire safety, drainage, and energy efficiency.
London Renovations manages planning coordination and compliance, ensuring projects progress without delays or legal issues.
How Long Does a House Extension Take?
While timelines vary, most London extensions follow a structured schedule:
- Design & approvals: 6–10 weeks
- Construction phase: 10–18 weeks
- Finishing & final sign-off: 2–4 weeks
Clear project management and sequencing are essential to minimise disruption and keep work on schedule.
Is a House Extension Worth the Investment?
In most cases, yes. A well-designed and professionally built extension can increase property value by 15–25%, particularly when it creates:
- Open-plan kitchen and dining areas
- Additional bedrooms or bathrooms
- Improved natural light and flow
Beyond resale value, extensions significantly improve daily living comfort, flexibility, and energy efficiency.
Why Choose London Renovations for Your House Extension?
London Renovations delivers fully managed house extension projects across London, combining design, construction, and compliance under one experienced team.
Clients benefit from:
- Transparent, itemised pricing
- Structural and architectural expertise
- Full planning and building regulation support
- Skilled craftsmanship and quality control
- Clear communication from start to completion
Start Planning Your House Extension
If you are considering a house extension in London, early planning and professional guidance make all the difference.
Contact London Renovations Ltd today to discuss your extension ideas and receive a tailored consultation focused on quality, value, and long-term performance.
