In Cambridge, a loft conversion costs between £25,000 and £65,000 depending on type and specification. This guide breaks down each type — Velux, dormer, hip-to-gable, mansard — so you can estimate before you quote.
Loft Conversion Cost by Type
| Type | Cost Range | Typical Timeline | Space Added |
|---|---|---|---|
| Velux / Rooflight | £25,000 – £35,000 | 6–8 weeks | Lowest head height |
| Dormer | £35,000 – £50,000 | 8–12 weeks | Significant head height |
| Hip-to-Gable | £40,000 – £55,000 | 10–14 weeks | Maximum space |
| Mansard | £50,000 – £75,000 | 12–16 weeks | Maximum head height |
Figures for Cambridge/South East, 2026. Prices include VAT.
Velux / Rooflight Conversion: £25,000 – £35,000
The simplest and cheapest loft conversion. You keep the existing roof shape and add rooflights for natural light.
What's Included
- Structural floor strengthening
- Insulation and plasterboarding
- Staircase installation
- 2–4 rooflights
- Electrics and lighting
- Plastering and decoration
Best For
Homes with good existing head height (2.2m+ at the highest point). If you can stand upright in your loft without ducking, a Velux conversion might work.
Limitations
- Head height drops to 1.8–2m at the edges
- Less floor space than other types
- May not need planning permission (often permitted development)
Dormer Conversion: £35,000 – £50,000
A dormer extends vertically from the roof slope, creating a box-shaped extension with vertical windows and a flat roof.
What's Included
- Structural alterations to the roof
- Dormer construction (timber frame, waterproofing)
- Windows (usually uPVC or aluminium)
- Internal fit-out (stairs, insulation, electrics)
Best For
Homes with limited head height. A dormer creates standing room across most of the loft space.
Cost Factors
- Size: A small dormer (2m × 3m) costs less than a full-width dormer
- Windows: uPVC is cheaper than aluminium or timber
- Bathroom: Adding an en-suite adds £8,000–£15,000
Hip-to-Gable Conversion: £40,000 – £55,000
Converts a hipped (sloping) roof into a gable (vertical) end, creating more internal space. Only works on semi-detached or end-terrace houses.
What's Included
- Removing the sloping roof section
- Building a new gable wall
- Extending the ridge
- Internal fit-out (often combined with a dormer at the rear)
Best For
Semi-detached and end-terrace houses with hipped roofs. Creates the most usable floor space of any conversion type.
Mansard Conversion: £50,000 – £75,000
The most complex and expensive conversion. Creates a double-sloped roof with a nearly flat top, maximising head height and floor space.
What's Included
- Major structural changes to the entire roof
- New timber frame construction
- Leadwork and waterproofing
- Dormer windows (typically 2–3)
- Full internal fit-out
Best For
Period properties, conservation areas, and homeowners wanting maximum space. Often requires planning permission.
Where Does the Money Go?
| Item | Percentage | Example (£45,000 conversion) |
|---|---|---|
| Structure (roof alterations, floor strengthening) | 35–45% | £15,750 – £20,250 |
| Windows and rooflights | 10–15% | £4,500 – £6,750 |
| Stairs | 5–10% | £2,250 – £4,500 |
| Insulation and plasterboarding | 10–15% | £4,500 – £6,750 |
| Electrics and plumbing | 5–10% | £2,250 – £4,500 |
| Fit-out (flooring, decoration) | 10–15% | £4,500 – £6,750 |
| Professional fees | 10% | £4,500 |
What Affects Your Final Price?
1. Head Height
If your loft has less than 2.2m head height at the ridge, you'll need more structural work — raising the roof or lowering the ceiling below. This adds £10,000–£20,000.
2. Staircase Location
Adding stairs is often the most complex part. If you can use an existing stairwell (by extending it upward), you save money. If you need a new stair opening, it costs more.
3. Bathroom / En-Suite
Adding a bathroom to the loft requires plumbing, waste pipes, and sometimes a pump. Budget £8,000–£15,000 extra.
4. Specification Level
Basic fit-out (carpet, painted walls, standard lighting) vs premium (oak flooring, recessed lighting, custom joinery) can vary the cost by £10,000–£20,000.
5. Planning Permission
Velux and small dormers often fall under permitted development. Large dormers, hip-to-gables, and mansards often require planning permission — which adds time and fees.
Is a Loft Conversion Worth It?
A loft conversion typically adds 10–20% to your home's value. In Cambridge, where property prices are high, this can be £50,000–£100,000 of added value — often exceeding the conversion cost.
Beyond financial return, a loft conversion adds usable space without losing garden. It's often cheaper and less disruptive than an extension or moving house.
Get a Quote for Your Loft Conversion
The figures in this guide are estimates based on projects we've completed in Cambridge. The only way to know what your loft conversion will cost is to get a detailed quote.
FAQ
How long does a loft conversion take?
Velux conversions: 6–8 weeks. Dormers: 8–12 weeks. Hip-to-gable and mansard: 10–16 weeks. Add 4–6 weeks for planning permission if required.
Do I need planning permission?
Velux and small rear dormers often fall under permitted development. Hip-to-gable and mansard conversions often require planning, especially in conservation areas.
Can I live in my house during a loft conversion?
Yes, in most cases. The work happens from outside using scaffolding. Internal disruption is limited to a few days when the stairs are installed.
How much value does a loft conversion add?
Typically 10–20% of the property value. In Cambridge, this can be £50,000–£100,000 depending on the property.