How Much Does a Loft Conversion Cost in the UK? (2026 Guide)
A no-nonsense breakdown of loft conversion costs in 2026 — by type, region and spec — plus the hidden extras most quotes miss.
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The short answer
In 2026, a typical UK loft conversion costs between £45,000 and £90,000 including VAT, depending on type, location and finish. London and the South East sit roughly 15–25% above the national average.
| Type | Typical cost (2026) | Best for |
|---|---|---|
| Velux / rooflight | £25,000 – £40,000 | Bungalows, big roofs |
| Dormer | £45,000 – £70,000 | Most semis & terraces |
| Hip-to-gable | £55,000 – £80,000 | End-of-terrace, semis |
| Mansard | £70,000 – £100,000+ | Period London terraces |
What drives the price
- Structural work — new steels, floor joists and stair openings are usually the biggest single line.
- Roof type — mansards rebuild the whole roof; Velux barely touches it.
- Bathroom — adding an ensuite typically adds £6,000–£12,000.
- Finish level — fitted wardrobes, oak floors and underfloor heating can add 20–30%.
- Access — scaffolding on a busy London street is materially more than a suburban driveway.
The extras most quotes miss
- Building control fees (£600–£1,200)
- Party wall agreements (£900–£2,500 per neighbour)
- Structural engineer's calcs (£600–£1,500)
- Utility upgrades (consumer unit, boiler)
- Making good downstairs after the new stair lands
If a quote doesn't list these, assume they're coming as variations later.
How to sanity-check a builder's number
Use Build Price IQ's cost checker to get an independent 2026 estimate in under a minute. If your quote is more than ~15% above the median, ask for a line-by-line breakdown before signing.