Key Takeaways
- A London loft conversion costs £25,000 to £100,000+ depending on type and specification.
- By type: Velux £25k to £45k, dormer £55k to £120k in London, hip-to-gable £45k to £65k, mansard £55k to £80k+ (Checkatrade / MyJobQuote / Architecture for London, 2026).
- London prices run 20 to 30% above national averages.
- A loft conversion adding a bedroom can add up to 24% to a property's value (Nationwide, 2025).
- Most conversions take 6 to 10 weeks on site.
A loft conversion is one of the smartest ways to add a bedroom, home office or en-suite to a London home without losing garden space. This guide breaks down what each type of conversion costs in 2026, what drives the price, and how much value it adds.
How much does a loft conversion cost in London?
A loft conversion in London costs between £25,000 and £100,000 or more in 2026, depending on the type of conversion and the finish. London prices run roughly 20 to 30% above national averages because of higher labour costs and stricter planning, particularly in conservation areas and Article 4 zones, according to Checkatrade and Architecture for London data.
| Loft conversion type | Best for | London cost |
|---|---|---|
| Velux / rooflight | Roofs with existing headroom | £25,000 to £45,000 |
| Dormer | Most London terraces, maximum space for money | £55,000 to £120,000 |
| Hip-to-gable | Semis and end-of-terrace homes | £45,000 to £65,000 |
| Mansard | Maximum space, period terraces | £55,000 to £80,000+ |
The four loft conversion types explained
Choosing the right type is the biggest single cost decision. Each suits a different roof shape and budget.
- Velux / rooflight: the cheapest option, adding windows into the existing roofline without altering its shape. Only works where you already have enough head height.
- Dormer: a box-shaped extension projecting from the roof slope that creates full-height usable space. The most popular London choice and the best value for the space gained.
- Hip-to-gable: extends a sloping hip end up to a vertical gable wall, ideal for semi-detached and end-of-terrace homes.
- Mansard: rebuilds the roof to an almost vertical rear slope, creating the most space and a traditional look favoured in conservation areas, but the most expensive and usually requires planning permission.
What affects the cost?
Beyond the type, the main cost drivers are head height, staircase position, the number of dormers and rooflights, en-suite plumbing, and whether structural steel is needed to support the new floor. Period properties often need additional work to bring the existing structure up to modern building regulations.
How much value does a loft conversion add?
Loft conversions are among the most rewarding projects financially. Nationwide's 2025 research found that adding a bedroom through a loft conversion or extension can boost a property's value by up to 24%, with a two-to-three bedroom conversion adding around 13%. In London's space-starved market, the extra bedroom or home office often pays back a large share of the cost.
How long does it take?
A typical London loft conversion takes 6 to 10 weeks on site, preceded by design, structural calculations and any planning application. We manage the whole process, from drawings and building control to the finished room. For a free quote, contact us or call 07472 424 226. Considering other options? Compare a house extension or read about which renovations add the most value.