A loft conversion is one of the most cost-effective ways to add living space and value to your home. Here's your complete guide to costs and conversion types in 2025.
A loft conversion is consistently ranked as one of the best home improvements you can make in the UK — and for good reason. It converts dead space into a beautiful, functional room with minimal impact on your garden or ground floor footprint. In Hampshire and Surrey, a well-executed loft conversion can add £40,000–£80,000+ to your property value.
Types of Loft Conversion & Costs
1. Velux / Roof Light Conversion (£20,000–£35,000)
The simplest and most affordable option. Velux windows are added to the existing roof slope, and the loft floor is strengthened. No change to the roofline means no planning permission required in most cases. Best suited to lofts with 2.3m+ of headroom at the ridge.
2. Dormer Conversion (£35,000–£60,000)
The most popular choice in the UK. A box-shaped structure is added to the rear roof slope, dramatically increasing headroom and floor area. A rear dormer typically falls within permitted development rights. A rear dormer with an en-suite bathroom is the single most popular home improvement project in the UK.
3. Hip-to-Gable Conversion (£40,000–£65,000)
Suitable for detached and semi-detached homes with hipped roofs. The sloped hip end is replaced with a vertical gable wall, dramatically increasing usable space. Often combined with a rear dormer to maximise the loft conversion potential.
4. Mansard Conversion (£50,000–£75,000+)
The most extensive option, involving a near-vertical rear wall (at least 72°) and a flat roof. Commonly seen in London terraced houses and conservation areas. Almost always requires planning permission. Offers the most headroom and floor space of all conversion types.
What's Included in the Cost?
- Structural calculations and building regulations drawings
- Strengthening of floor joists
- Staircase installation (£3,000–£8,000 depending on design)
- Insulation, plasterboard, and plastering
- Velux windows or dormer structure
- Electrical first and second fix
- Bathroom/en-suite plumbing if required
Do You Need Planning Permission for a Loft Conversion?
Most loft conversions fall within permitted development rights, provided:
- The volume added doesn't exceed 50m³ (detached/semi) or 40m³ (terraced)
- No extension beyond the existing roof plane on the principal elevation (front)
- No verandas, balconies, or raised platforms
- Materials are similar to the existing house
You'll always need building regulations approval for a loft conversion, regardless of planning status.
Return on Investment
Research consistently shows that a well-executed loft conversion adds between 15–25% to a property's value in South East England. A dormer conversion costing £45,000 in a £400,000 home could add £60,000–£100,000 in value — a strong return on investment.
| Conversion Type | Average Cost | Typical Value Added | ROI |
|---|---|---|---|
| Velux | £25,000 | £30,000–£45,000 | 120–180% |
| Dormer | £45,000 | £55,000–£85,000 | 122–189% |
| Hip-to-Gable | £55,000 | £65,000–£90,000 | 118–164% |
| Mansard | £65,000 | £75,000–£100,000 | 115–154% |
Planning a project in Hampshire or Surrey?
Fortis Construction & Maintenance offer free, no-obligation quotes. Our team has decades of experience with extensions, loft conversions and full renovations.
The Fortis Team
Fortis Construction & Maintenance
With decades of experience delivering extensions, loft conversions, and full renovations across Hampshire & Surrey, the Fortis team shares expert knowledge to help homeowners make informed decisions.
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