Calculate your loft conversion cost
Loft conversion cost by type in London
The national source benchmarks below are for typical 30m² projects.
UK £22,500–£30,000£28,800–£38,400
UK £40,000–£60,000£51,200–£76,800
UK £50,000–£70,000£64,000–£89,600
UK £50,000–£80,000£64,000–£102,400
What the regional adjustment changes
What can change a real London quote?
- Velux, dormer, hip-to-gable, mansard or shell-only type
- Usable new floor area
- Roof structure and existing head height
- New staircase position and specification
- Structural steel and roof alterations
- Ensuite, electrics, heating and finish level
- Region, access and scaffolding
Local planning considerations
Dense access, parking, deliveries and contractor overheads can widen the spread between quotations, so use the figures as an early budget rather than a quote.
- Allow separately for parking, loading, permits or restricted delivery windows where a property has difficult street access.
- Flats and managed buildings can add landlord, freeholder or building-management requirements that are outside a basic works estimate.
- Party-wall, structural and access costs should be checked independently on extensions, lofts and major internal alterations.
How the regional model works
The 1.28× factor places this planning estimate 28% above the national planning baseline. We keep that modelling assumption separate from the dated national benchmark so users can see which part comes from an external source and which part is UK Home Costs modelling.
Sources
Loft Conversion Cost: 2026 UK Price Guide & Breakdown
Published / checked: March 2026
Used for: Loft conversion type benchmarks
Construction output price indices
Published / checked: 13 August 2026
Used for: Construction price trend and update checks
Frequently asked questions
How much does a loft conversion cost in London in 2026?
Our modelled London ranges run from about £28,800–£38,400 for a 30m² Velux or rooflight conversion to about £64,000–£102,400 for a 30m² mansard.
How much is a dormer loft conversion in London?
The modelled planning range for a typical 30m² dormer is about £51,200–£76,800, starting from the current national £40,000–£60,000 benchmark.
Why is the London estimate different from the UK benchmark?
The 1.28× London factor places the model 28% above the national planning baseline. It is a planning assumption, not an observed city-wide contractor index.
What can push a loft conversion above the modelled range?
Staircase changes, structural steel, low head height, complex roof alterations, an ensuite, premium finishes, difficult access and fire-safety work can increase the final quote.