What Does a Loft Conversion Cost?
Quick Answer
Velux £15,000–£40,000. Dormer £30,000–£60,000. Mansard £45,000–£80,000
Guide prices from published 2026 UK cost guides, not quotes. Most conversions work out at roughly £1,200–£1,800 per m² of new floor area outside London
Loft Conversion Costs by Type (2026 UK)
The table collates the major published 2025–2026 UK cost guides (MyJobQuote, Checkatrade, PriceYourJob, HomeHow). The guides genuinely disagree on some types, so where they do, the range shows the full spread rather than a false average. Every figure is a national guide price for a finished habitable room: get itemised local quotes before budgeting.
| Conversion type | Guide price | Notes |
|---|---|---|
| Velux / rooflight | £15,000–£40,000 | No change to the roof shape. Guides disagree most here: MyJobQuote prices a 30m² job at £15,000–£20,000 while Checkatrade’s average is around £27,500 |
| Rear dormer | £30,000–£60,000 | The most popular type; around £45,000 is a typical mid-point for a medium dormer conversion |
| Hip-to-gable | £40,000–£70,000 | Builds the hipped roof slope up into a vertical gable; often combined with a rear dormer on semis. Span across MyJobQuote’s guides: its dedicated hip-to-gable guide prices standard jobs at £40,000–£65,000 (high-spec £55,000–£75,000+), and its general guide’s 50m² band runs £55,000–£70,000 |
| Hip-to-gable + rear dormer | £50,000–£80,000 | Maximum space on a hipped-roof semi. No national guide prices the combination directly: specialists add £10,000–£15,000 for the rear dormer on top of hip-to-gable rates, and London design-and-build packages run £70,000–£90,000 |
| Mansard | £45,000–£80,000 | Rebuilds the whole roof slope to near-vertical; the most expensive type and it usually needs planning permission. MyJobQuote’s general loft guide prices 30–50m² mansards at £45,000–£70,000 and its dedicated mansard guide at £55,000–£80,000 (£70,000–£90,000 in central London); Checkatrade quotes £45,000–£75,000+ and MyBuilder’s average is £67,500 |
| Bungalow loft conversion | ~£35,000 | MyJobQuote’s single published average; treat as indicative only, the staircase position is usually the deciding factor |
| Rate per m² of new floor area | £1,200–£1,800 | National guide band; MyJobQuote prices hip-to-gable at £1,400–£2,000 per m², modular at £1,800–£2,500 and mansard at £1,750–£3,000 per m². London runs £1,800–£2,700 per m² |
Extras That Add Cost
| Item | Guide price | Notes |
|---|---|---|
| En-suite bathroom | £5,000–£12,000 | Plumbing runs and a shower room; size the space first with the loft bathroom calculator |
| Staircase, standard | £1,500–£2,500 | Off-the-shelf flight fitted; other guides price standard flights to £3,000, and bespoke or space-saver designs run £5,000–£10,000+ |
| Party wall agreement | £700–£2,700 | Per agreement across guides; a single agreed surveyor keeps it near £1,000, while separate surveyors for each owner can double the bill |
| Planning application, if needed | £548 | England householder fee from 1 April 2026; fees now rise with CPI every April. Many lofts fall under permitted development instead |
Where the Money Goes
Structural work drives the budget: new floor joists, steel beams, the dormer or gable build, and the staircase. Labour is typically the largest single share of the bill. Check whether your roof needs steel with the loft steel beam calculator, confirm usable space with the head height calculator, and plan the stair opening with the staircase space calculator.
Planning Permission and Permitted Development
Most Velux conversions and many rear dormers fall within permitted development: up to 40m³ of additional roof space on a terraced house, 50m³ on a semi or detached house, subject to conditions. Mansards almost always need planning permission. Check your volume allowance with the loft PD volume calculator, and see the planning fee schedule if you do need to apply.
What Affects the Price
- Conversion type: the more the roof shape changes, the more it costs. Velux is cheapest, mansard dearest
- Size: bigger lofts cost more in total but less per m²
- Structure: cut roofs convert more easily than modern trussed-rafter roofs, which need re-engineering
- Bathroom: an en-suite adds £5,000–£12,000 plus plumbing complexity
- Staircase position: a straightforward stacked stair is cheap; rearranging the floor below is not
- Head height: below about 2.2m at the ridge, costs rise sharply because the roof or floor must move
- Spec: glazing, flooring and built-in storage move the total significantly either way
London and the South East
Every guide we checked prices London and the South East above these national figures. MyJobQuote puts the general premium at 15–25% and quotes London at £1,800–£2,700 per m² against £1,250–£1,900 in the north; its dormer guide runs the premium to 30%. Budget towards or above the top of each range in London.
Timescales
- Velux / rooflight: 4–6 weeks on site
- Dormer or hip-to-gable: 6–8 weeks
- Mansard: 8–10 weeks
- Guides differ on programme: MyBuilder quotes 6–8 weeks for Velux jobs and 10–14 for roof-altering types, so agree a written programme with your builder
- Allow extra lead time for design, structural calculations, building regulations and any planning application before work starts
Important Notes
- All figures are guide prices from published 2025–2026 UK cost guides, not quotes: get at least three itemised quotes
- Cost guides commonly cite a value uplift of around 10–20% for a well-executed conversion with a bedroom and bathroom; treat that as indicative, it varies by area
- Every habitable loft conversion needs building regulations approval, including fire escape provision and protected stairs
Figures cross-checked against published UK cost guides July 2026. Last updated: July 2026