Guide prices, before you've told us anything.
Real ranges by conversion type, a full worked breakdown of a typical dormer, and exactly what's excluded — so you can compare us against anyone else quoting.
| Type | Range | Typical | On site |
|---|---|---|---|
| Rooflight (no structural change) | £24,000–£36,000 | £29,000 | 5–7 weeks |
| Rear dormer | £38,000–£58,000 | £46,500 | 7–11 weeks |
| Hip-to-gable | £46,000–£68,000 | £55,000 | 8–12 weeks |
| L-shaped dormer | £56,000–£82,000 | £67,000 | 9–13 weeks |
| Mansard | £68,000–£98,000 | £80,000 | 12–18 weeks |
Guide ranges for West Yorkshire, England. Sources: Checkatrade cost guide (updated March 2026) and the HomeOwners Alliance (updated July 2026), which agree closely. Prices vary by region — city centres typically run higher than the surrounding area. Every one of these is confirmed in writing after a survey — none of them is a quotation.
Conversion types explained
Rooflight / Velux
No structural change to the roofline — new floor, insulation, rooflights. The cheapest route to a usable room, and often permitted development.
Rear dormer
The most common route for a terrace or semi. Adds full standing height and floor area across most of the rear roof slope.
Hip-to-gable
Turns a hipped roof end into a vertical gable wall, adding width before a dormer is even considered. Common on semis and detached houses.
Mansard
Replaces most of the roof structure for maximum usable space — the biggest structural job, and usually needs full planning permission.
32m² rear dormer, West Yorkshire, mid specification, one en-suite
- Roof coverings£7,600Tiles, lead, felt, guttering, making good the existing roof
- Internal preparation£6,400Strip out, chimney work, moving tanks and services
- Structural steels£8,900Design, supply and fit, sized by the structural engineer
- Staircase£4,200Design, joinery, balustrade to current regulations
- First & second fix£11,300Electrics, plumbing, insulation, plastering, flooring
- En-suite£5,600Fittings, tiling, waterproofing, extraction
- Decoration & snagging£2,500Final finish and the walkthrough before sign-off
Included, excluded, and priced.
Included
- Survey, drawings & structural calcs✓
- Party wall notices & building control✓
- Scaffold, skip, welfare on site✓
- Full decoration to a paint-ready finish✓
Excluded (priced separately)
- Bathroom sanitaryware & tiling above standard specfrom £2,200
- Fitted wardrobes / joinery beyond the standard buildfrom £1,800
- New boiler if the existing one can't copefrom £3,000
- Skylights beyond the two included as standardfrom £950 each