Calculate Your Dormer Loft Conversion Cost
2026 Dormer Loft Conversion Cost Guide
Dormer loft conversions are one of the most cost-effective ways to add living space to a UK home. Below are typical 2026 cost ranges by dormer type:
| Dormer Type | Low | High |
|---|---|---|
| Flat-Roof Dormer | £30,000 | £60,000 |
| L-Shaped Dormer | £45,000 | £75,000 |
| Hip-to-Gable | £40,000 | £65,000 |
| Mansard Dormer | £45,000 | £70,000+ |
Frequently Asked Questions
How much does a dormer loft conversion cost in the UK in 2026?
A dormer loft conversion in the UK typically costs between £30,000 and £75,000 in 2026, depending on dormer type, location, size and finish. A flat-roof dormer averages £30,000–£60,000, while a mansard can reach £45,000–£70,000 or more.
Do I need planning permission for a dormer loft conversion?
Most dormer loft conversions fall under Permitted Development rights in England and Wales, so full planning permission is not usually required. However, properties in conservation areas or listed buildings will require it. Always check with your local planning authority first.
Is VAT charged on a dormer loft conversion?
No. Dormer loft conversions on existing residential properties are zero-rated for VAT purposes in the UK. This means no 20% VAT is added to the build cost, making loft conversions more affordable than other types of construction work.
How much value does a dormer loft conversion add to a house?
A dormer loft conversion typically adds 10–20% to a property's value. In London and the South East, a high-quality conversion with an en-suite bedroom can add £50,000–£100,000 or more. In other regions, expect a value uplift of £20,000–£50,000 depending on the local market.
How long does a dormer loft conversion take?
On site, a dormer loft conversion typically takes 6–12 weeks to complete. Pre-construction phases — including architectural drawings, building regulations approval and (if needed) planning permission — add a further 8–16 weeks. Budget for a total project timeline of 4–6 months from start to finish.