Calculate your loft conversion cost
Loft conversion cost by type in Cardiff
The national source benchmarks below are for typical 30m² projects. The Cardiff column applies the same 0.91× regional model to each type.
UK £22,500–£30,000£20,500–£27,300
UK £40,000–£60,000£36,400–£54,600
UK £50,000–£70,000£45,500–£63,700
UK £50,000–£80,000£45,500–£72,800
What the regional adjustment changes
What can change a real Cardiff 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
For grants and energy schemes, verify the current Wales-specific eligibility rules before relying on any support assumption.
- Use Wales-specific planning, building-control and energy-scheme information where the rules differ from England.
- Terraced or constrained urban properties can add access, waste and scaffold costs that are not captured by the regional factor.
- Drainage, roof and external-work scopes should be based on the property condition rather than a generic city assumption.
How the regional model works
The 0.91× factor places this planning estimate 9% below the national planning baseline. We keep that modelling assumption separate from the dated national benchmark so users can see exactly 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 Cardiff in 2026?
Our modelled Cardiff ranges run from about £20,500–£27,300 for a 30m² Velux or rooflight conversion to about £45,500–£72,800 for a 30m² mansard, using current national type benchmarks and the Wales regional factor.
How much is a dormer loft conversion in Cardiff?
The modelled Cardiff planning range for a typical 30m² dormer is about £36,400–£54,600. It starts from the current national £40,000–£60,000 benchmark and applies the Wales factor.
Why is the Cardiff estimate different from the UK benchmark?
UK Home Costs applies a 0.91× Wales planning factor, which places the model 9% below the national planning baseline. The factor is a transparent modelling assumption and not an observed city-wide contractor price 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 all increase the final quote.