How Much Does a House Extension Cost in London in 2025?
Expanding your home can be one of the most rewarding investments you’ll ever make. Adding not just space, but long-term value. This guide from PAR Group outlines realistic 2025 cost ranges in London. See what drives pricing, and how our Design & Build delivery keeps projects on time and on budget.
Average Extension Costs in London (2025)
House extension prices vary across the capital, but here’s a practical guide for 2025:
What Affects the Cost of Your Extension?
1) Size & Structural Complexity
Larger footprints, steel frames, vaulted ceilings, and extensive glazing increase both materials and labour.
2) Design & Specification Level
Standard specs will cost less than schemes with bespoke cabinetry, imported stone, or statement appliances.
3) Planning & Building Regulations
Some projects fall under permitted development, while conservation areas and listed properties require
full planning and additional detail.
4) Access & Location
Tight London sites and limited delivery access extend programme times and logistics costs.
5) Professional & Project Management Fees
Architecture, structural eng
Why Design & Build Saves Time and Money
Hiring separate designers and contractors can create gaps in scope, cost, and timeline. Our integrated Design & Build service brings architects, engineers, and craftsmen under one roof for:
• A single point of contact from concept to completion
• Accurate cost control from the earliest stage
• Seamless coordination and faster delivery
• Full transparency — no hidden extras
Case Study: Richmond Double-Storey Extension
Size: 65 m²
Timeline: 7 months
Budget: £165,000 (including interior fit-out)
Features: Open-plan kitchen with bespoke oak joinery, Crittall-style glazing, underfloor heating.
The result: a contemporary living space that respects the property’s character, delivered within budget
and ahead of schedule.
What Value Can an Extension Add?
A well-executed extension can add 10–25% to your property’s market value, depending on location and
finish, often translating into six-figure equity gains in London.
