Loft conversion cost breakdown in the UK
A UK loft conversion typically breaks down as 30% structural work, 15% roofing, 10% staircase, 8% electrics, 8% plumbing, 20% internal finishes and 9% professional fees. For a £50,000 dormer conversion, expect £15,000 on steels and carpentry, £7,500 on roofing, £5,000 on stairs and £10,000 on plaster, decoration and flooring.
Homeowners researching this typically also price up loft conversion cost in the uk, house extension cost in the uk and extension cost per m² in the uk. For wider context, browse our bathroom pricing, kitchen pricing and boiler & heating costs.
Cost table
| Item | Typical range (GBP) |
|---|---|
Structural steels (RSJs, beams) | £1,200–£3,500 |
Structural carpentry (floor joists, dormer frame) | £6,000–£12,000 |
Roofing (felt, battens, tiles, lead) | £2,500–£6,000 |
Staircase (design, build, install) | £1,200–£3,000 |
Electrics (lighting, sockets, smoke, data) | £1,500–£3,000 |
Plumbing (en-suite, heating, soil pipes) | £2,000–£4,500 |
Windows / Velux / dormer glazing | £1,500–£4,000 |
Insulation (floor, walls, roof) | £1,200–£2,800 |
Plastering & decoration | £2,000–£4,500 |
Flooring (engineered, carpet) | £800–£2,200 |
Architect / structural engineer | £1,500–£4,000 |
Building Control fees | £500–£1,000 |
Labour costs
Labour is roughly 50% of the total. Structural carpenters, roofers and general builders dominate the hours.
| Item | Typical range (GBP) |
|---|---|
Structural carpentry & dormer build | £8,000–£16,000 |
Roofing team | £2,500–£6,000 |
Staircase specialist | £1,200–£3,000 |
Electrician | £1,500–£3,000 |
Plumber | £2,000–£4,500 |
Plasterer / decorator | £3,000–£6,500 |
Materials costs
Materials include structural timber, steels, insulation, glazing, plasterboard, flooring and bathroom fittings.
| Item | Typical range (GBP) |
|---|---|
Steel beams (RSJs) | £1,200–£3,500 |
Structural timber (joists, studs, rafters) | £2,000–£5,000 |
Insulation (PIR + loft roll) | £1,200–£2,800 |
Velux / dormer windows | £1,500–£4,000 |
Bathroom suite & fittings | £1,500–£4,500 |
Flooring (engineered or carpet) | £800–£2,200 |
Factors affecting cost in the UK
- ·Conversion type — Velux is cheapest; mansard the most expensive.
- ·Structural complexity — steel beam sizes and bearing points.
- ·Roof pitch and height — steeper roofs are harder to work on.
- ·Party Wall agreements in terraced and semi-detached homes.
- ·Conservation areas and Article 4 directions.
Ways to reduce cost
- ·Use a design-and-build specialist for fixed-price certainty.
- ·Stay within permitted development to avoid planning fees.
- ·Skip the en-suite if a bathroom already sits below the loft.
- ·Use standard-size Velux windows rather than bespoke glazing.
- ·Get NHBC- or FMB-registered contractors.
Frequently asked questions
- What is the most expensive part of a loft conversion?
- Structural work — steels, floor joists and dormer carpentry make up roughly 30% of the budget.
- Can I do any of the work myself?
- Decoration, painting and basic flooring are DIY-friendly. Structural, roofing and electrics must be done by professionals.
- Do I need an architect for a loft conversion?
- For permitted development, a structural engineer is sufficient. For planning-required conversions, an architect is advisable.
- How much value does a loft conversion add?
- A well-executed dormer conversion typically adds 15–20% to a property's value, often £40,000–£80,000.
- Are loft conversions VAT-able?
- Yes, at 20% for most contractors. Some accessibility-focused adaptations may qualify for reduced rate.