Dormer Loft Conversion Cost & Options 2026 (UK)
A dormer loft conversion costs £30,000–£60,000 in 2026, with a modest rear dormer bedroom at the lower end and a large dormer with an en-suite and high-end finish towards the top. A dormer is the most popular loft conversion because it adds real headroom and floor space at a sensible price, and usually falls under permitted development. Here are the 2026 costs, the options, the planning rules and how much value it adds.
2026 dormer loft conversion costs
| Conversion | Typical cost (2026) | Notes |
|---|---|---|
| Small rear dormer (single bedroom) | £30,000–£40,000 | No en-suite, standard finish |
| Dormer with en-suite | £40,000–£50,000 | Extra plumbing and fit-out |
| Large / full-width dormer | £50,000–£60,000+ | More structure, higher finish |
| Roof light (Velux) conversion | £20,000–£30,000 | Cheaper alternative, less space |
| Architect & structural fees | £1,500–£4,000 | Drawings, calcs, building control |
What drives the price
The size of the dormer and the amount of new structure are the main factors, followed by whether you add an en-suite, the quality of the finish, staircase position and any steel beams needed. Access, scaffolding and how much the existing roof has to be opened up also move the number. A full-width rear dormer costs more than a modest box dormer but yields a proper double bedroom.
Do you need planning permission?
Many rear dormers fall under permitted development and do not need full planning permission, provided they stay within the volume limits and design rules — but they always need building regulations approval for structure, fire safety and insulation. Front-facing dormers, flats and homes in conservation areas usually do need planning. A good builder or architect will confirm before work starts.
Does a dormer add value?
A well-built dormer adding a double bedroom and en-suite is one of the strongest returns in home improvement, often adding more to the value than it costs in the right area. It also avoids the cost and disruption of moving house for an extra bedroom, which is why loft conversions remain so popular.
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