Loft conversion cost in the UK
A loft conversion in the UK typically costs between £30,000 and £75,000, with the most common dormer conversion landing around £45,000–£60,000 including a new staircase, bedroom and en-suite. A simple Velux (rooflight) conversion starts near £25,000; a full mansard in a London terrace can reach £85,000–£100,000.
Homeowners researching this typically also price up house extension cost in the uk, builder day rate in the uk and roof repair cost in the uk. For wider context, browse our bathroom pricing, kitchen pricing and boiler & heating costs.
Cost table
| Item | Typical range (GBP) |
|---|---|
Velux / rooflight conversion | £25,000–£40,000 |
Dormer conversion (most common) | £40,000–£65,000 |
Hip-to-gable conversion | £50,000–£75,000 |
L-shaped dormer (Victorian terrace) | £55,000–£80,000 |
Mansard (London / conservation areas) | £70,000–£100,000 |
Labour costs
Labour accounts for around 50% of a loft conversion. The structural work, joinery and finishing trades dominate.
| Item | Typical range (GBP) |
|---|---|
Structural carpentry & dormer build | £8,000–£16,000 |
Roofing (felt, tiles, lead flashings) | £2,500–£6,000 |
Staircase install | £1,200–£3,000 |
Plumbing & en-suite fit | £2,000–£4,500 |
Electrical (lighting, sockets, smoke) | £1,500–£3,000 |
Plaster, decoration, flooring | £3,000–£6,500 |
Materials costs
Materials include structural steels, insulation to current Building Regs, glazing, plus all internal finishes.
| Item | Typical range (GBP) |
|---|---|
Steel beams (RSJs) | £1,200–£3,500 |
Insulation (PIR + loft roll) | £1,200–£2,800 |
Velux windows (each) | £450–£1,200 |
Dormer window & glazing | £1,500–£4,000 |
Bathroom suite & fittings | £1,500–£4,500 |
Flooring (engineered or carpet) | £800–£2,200 |
Cost per m² of new loft floor area
| Item | Typical range (GBP) |
|---|---|
Velux conversion | £1,100–£1,500/m² |
Dormer | £1,500–£2,100/m² |
Mansard | £2,200–£2,900/m² |
Factors affecting cost in the UK
- ·Conversion type — Velux is cheapest, mansard the most expensive.
- ·Existing roof height — under 2.2 m may need a raised ridge.
- ·Party Wall agreements in terraced and semi-detached homes (£700–£1,500 per neighbour).
- ·Bathroom inclusion adds £4,000–£8,000 over a plain bedroom.
- ·Conservation areas and Article 4 directions in London restrict permitted development.
Ways to reduce cost
- ·Choose a design-and-build loft specialist over architect + separate contractor for fixed-price certainty.
- ·Stay within permitted development volumes (40 m³ terraced, 50 m³ detached) to avoid full planning.
- ·Avoid en-suite if a bathroom already sits below the loft to save plumbing runs.
- ·Use standard-size Velux windows rather than bespoke dormer glazing.
- ·Get NHBC- or FMB-registered contractors to avoid expensive remedial works.
Frequently asked questions
- Do I need planning permission for a loft conversion?
- Many fall under permitted development. Rear dormers on terraced houses, conservation areas and flats always need planning permission.
- How much value does a loft conversion add?
- Nationwide data suggests adding a bedroom and bathroom through a loft conversion adds 15–20% to UK property value.
- How long does a loft conversion take?
- 8–12 weeks for Velux and dormer; 12–16 weeks for hip-to-gable and mansard.
- Can any loft be converted?
- Most can, but minimum head height of 2.2 m at the highest point is needed. Trussed roofs can be converted but cost more due to structural rework.
- Do I need a Party Wall Agreement?
- Yes, in nearly all terraced and semi-detached properties — required under the Party Wall Act 1996 before structural work starts.
- Is a fire-rated staircase required?
- Yes — Building Regs require a 30-minute fire-protected escape route from the loft to the front door in homes converted to 3 storeys.