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.
Planning the work? Check what it usually costs, or work out your own estimate. The free quote form is at the top of this page.
Average roof conversion cost by type — 2026
Typical finished cost, standard specification. Source: BestBuilders 2026 regional cost model · 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.