Average Cost of a Roof Conversion in 2026 (UK)
A roof conversion — turning your loft or roof space into a room — costs on average £40,000–£70,000 in 2026. The range is wide because the roof itself decides the price: a simple rooflight (Velux) conversion starts near £27,000, a dormer runs £45,000–£75,000, and a full mansard reaches £90,000. This insights piece shows the average by conversion type, what moves the number, and where to get the detailed, quote-ready figures for the type you are planning.
Average roof conversion cost by type — 2026
Typical finished cost, standard specification. Source: BestBuilders 2026 quote data · 519 UK towns
Average Roof Conversion Cost by Type
These are the headline 2026 ranges. For a full breakdown of any one type — what is included, cost per square metre and regional pricing — follow the link in each row to that type’s own cost guide.
| Conversion type | Average cost (2026) | Best for |
|---|---|---|
| Rooflight / Velux | £27,000–£45,000 | Roofs with enough head height already |
| Dormer | £45,000–£75,000 | Adding head height and floor space |
| Hip-to-gable | £48,000–£72,000 | Semi and end-of-terrace hipped roofs |
| L-shaped dormer | £55,000–£85,000 | Victorian terraces with a rear addition |
| Mansard | £60,000–£90,000 | Maximum space, period streets |
Ranges are for a finished room to a standard specification, including the staircase and an en-suite where noted. For the full pricing model and per-town figures, see the loft conversion cost guide and the attic conversion cost guide.
What Moves the Average
Two identical-looking lofts can be £20,000 apart. These are the factors that decide where you land in the range:
- Head height and roof shape — if you already have 2.2m under the ridge, a rooflight conversion may be all you need; if not, a dormer or mansard adds cost fast.
- Staircase position — fitting a compliant stair without losing a bedroom below is one of the trickiest, most cost-sensitive parts of the job.
- En-suite — adding a bathroom typically adds £5,000–£9,000 in plumbing, waterproofing and fittings.
- Structural work — new steels, floor joists and a strengthened party wall push the figure up on terraces and older roofs.
- Specification — glazing, flooring, built-in storage and heating choices move the finish from standard to premium.
- Region — London and the South-East typically run 20–30% above the national average.
How Long a Roof Conversion Takes
Most roof conversions are a 6–12 week job on site, depending on how much of the roof changes:
| Type | Typical time on site | Planning? |
|---|---|---|
| Rooflight / Velux | 5–6 weeks | Usually permitted development |
| Dormer (rear) | 7–8 weeks | Often PD; front dormer needs consent |
| Hip-to-gable | 8–9 weeks | Often PD within limits |
| Mansard | 10–12 weeks | Usually needs planning permission |
Add design, structural calculations and any planning decision (about 8 weeks) before work starts. See loft conversion planning permission and our front dormer planning guide.
Is a Roof Conversion Worth It?
As an investment, a roof conversion is one of the stronger home improvements. A well-executed conversion that adds a double bedroom and en-suite typically adds around 15–20% to a property’s value, and in high-demand areas the uplift can cover most of the build cost. The gain is largest when the conversion turns a two-bed into a three-bed, or a three into a four, because it moves the house into a different buyer bracket. It is weakest when the finished room is compromised — poor head height, an awkward stair, or an obvious box dormer on a period street. Get the type right for the roof you have, and the numbers usually work.
Choosing a Specialist: Your Checklist
These are checks you make before appointing anyone:
- Ask to see two recent conversions of the same type you can visit or phone about.
- Confirm the quote covers the staircase, building control fees and finishes — not just the shell.
- Ask to see current public liability insurance and check the level yourself.
- For structural work, ask who provides the engineer’s calculations and confirm building control is involved.
- Get three fixed quotes on the same drawings and specification so the figures are genuinely comparable.
Roof Conversion Costs — FAQs
Most roof (loft) conversions cost £40,000–£70,000 in 2026. A simple rooflight conversion can start near £27,000, while a full mansard can reach £90,000. London and the South-East typically run 20–30% higher.
A rooflight or Velux conversion, because the roof structure barely changes — you add windows in the existing slope, insulation, a stair and finishes. It only works if you already have enough head height under the ridge.
Many rear dormer and rooflight conversions are permitted development within size limits, but a front dormer or a mansard usually needs a full application. Check our loft conversion and front dormer planning guides before you commit.
A conversion adding a double bedroom and en-suite typically adds around 15–20% to a property’s value, and the uplift is largest when it moves the home into a higher bedroom bracket.
Around 5–6 weeks for a rooflight conversion, 7–9 weeks for a dormer or hip-to-gable, and 10–12 weeks for a mansard, plus design and any planning decision beforehand.
Related Cost Guides
Detailed pricing for each conversion type.