Loft Conversion Costs
2026 London Loft Conversion Cost & Price Guide
Transparent pricing, RIBA architectural design, and guaranteed build timelines for London homes.
- ✓ RIBA-Led Practice: In-house architectural team handling council planning approvals and structural designs.
- ✓ Clear Fixed-Price Quotes: Detailed, itemised budgets before construction starts with no hidden extras.
- ✓ 10-Year Guarantee: Comprehensive insurance-backed structural protection on all builds.
Estimated Cost Guidance
Average baseline costs for loft conversions across London and the Home Counties:
| Conversion Type | Project Scope | Avg Timeline | Estimated Price |
|---|---|---|---|
| Rooflight / Velux Conversion | Floor reinforcement, roof windows, insulation, stair installation | 4–6 Weeks | From £35,000+ |
| Main Rear Dormer | Rear extension wall, additional double bedroom & en-suite bathroom | 6–8 Weeks | From £45,000+ |
| Hip-to-Gable Conversion | End-terrace / semi-detached hip roof extension to vertical gable | 7–9 Weeks | From £55,000+ |
| Mansard Conversion | Full-width conversion with 72-degree rear slope (ideal for period homes) | 8–10 Weeks | From £65,000+ |
What Drives Your Loft Conversion Cost?
Loft conversion budgets vary based on several key architectural and structural factors:
- Plumbing & En-Suites: Adding a luxury en-suite or wet room requires upgraded boiler capacity, pumps, and new soil pipe connections.
- Planning Permission: Permitted Development rights apply to many rear dormers, but full planning permission is needed in Conservation Areas or for front dormers.
- Structural Alterations: Steel beam positioning, water tank relocations, and custom staircase design to fit existing floor plans seamlessly.
Contact Us
Telephone 020 8898 8299
Office address:
12 High Street, Hampton Wick, Kingston upon Thames, KT1 4DB
Street view
Interior view
Company number 11454709. VAT number 299773521
Request Quotation
Request Your Free Architectural Consultation & Estimated Costing Complete this short assessment to receive a tailored, itemised quote from our RIBA architectural team.
Request Quotation
Request Your Free Architectural Consultation & Estimated Costing Complete this short assessment to receive a tailored, itemised quote from our RIBA architectural team.
Contact Us
Telephone 020 8898 8299
Office address:
12 High Street, Hampton Wick, Kingston upon Thames, KT1 4DB
Street view
Interior view
Company number 11454709. VAT number 299773521
