Types of Loft Conversions and What They Cost UK
Not all loft conversions are the same. The right type for your home depends on your roof structure, budget, and how much additional space you need. Here's the full breakdown.
Loft Conversion Types at a Glance
| Type | Best For | Cost Range | Planning Usually Needed |
|---|---|---|---|
| Velux / Rooflight | Lofts with good head height, tight budgets | £15,000–£30,000 | No (Permitted Development) |
| Rear Dormer | Most common, terraced and semi-detached | £30,000–£55,000 | Usually no |
| Double / Corner Dormer | Maximum head height and floor area | £45,000–£75,000 | Possibly |
| Mansard | Detached properties, maximum space, flat roof | £60,000–£100,000 | Yes — full planning |
| Hip-to-Gable + Dormer | Detached homes, large loft conversion | £70,000–£120,000 | Yes — full planning |
Velux / Rooflight Conversion
The simplest and cheapest option. Velux windows are installed into the existing roof slope. No structural changes to the roof — just new windows and a staircase, plus insulation and lighting.
Key requirements:
- Minimum 2.3m of head height at the tallest point (or achievable with floor lowering)
- Sufficient landing space at the bottom for a staircase
- Roof slope must be at least 30° for Velux windows to work well
Planning: Velux installations usually fall under Permitted Development — no full planning application needed. Building Regulations approval is still required.
Rear Dormer
A dormer extends vertically from the roof, creating a box-shaped addition with a flat or pitched roof. The most common type in the UK because it adds the most usable floor space without changing the main roof profile.
Why it's popular: Rear dormers are invisible from the road, so they typically don't require full planning permission even in conservation areas. They create excellent full head height and allow standard windows.
Mansard Conversion
A mansard alters the roof slope to create a near-vertical wall with a shallow-pitched roof. It adds the most floor area of any conversion type but requires a flat or mansard roof to already exist — or significant structural work.
Planning: Almost always requires full planning permission as it changes the roof profile. Common in London where space is at a premium.
What Else Affects Cost
- Access staircase — if you're converting a 3-bedroom to a 4-bedroom, a proper staircase is required. Adds £3,500–£7,500.
- En-suite bathroom — adds £3,000–£8,000 if plumbing is extended to the loft.
- Fire safety upgrades — compartmentalisation and escape windows are required by Building Regulations.
- Property type — detached homes have easier access for steel beams. End-terrace and mid-terrace are more constrained.
- Existing condition — if the structure needs repairs or asbestos removal, costs rise quickly.
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