A loft conversion is one of the most popular and cost-effective ways to add an extra bedroom, bathroom or home office to your home. Here is everything you need to know.
Types of Loft Conversion
Velux / Rooflight Conversion
The simplest and cheapest option. No changes to the roof structure - just roof windows (Velux or similar) installed into the existing roof slope. Works best when there is already sufficient headroom in the loft.
- Cost: £20,000-£35,000
- Planning permission: rarely needed
Dormer Conversion
The most common type. A box-shaped structure is built out from the rear roof slope, creating additional headroom and floor space. Available as a single dormer or full-width dormer.
- Cost: £35,000-£60,000
- Planning permission: usually permitted development (rear dormers)
Hip-to-Gable Conversion
The sloping side of a hipped roof is extended vertically to create a gable end, increasing the usable loft space. Common on semi-detached and detached houses with hipped roofs.
- Cost: £40,000-£65,000
- Planning permission: may be permitted development on detached houses; usually needs permission in conservation areas
Mansard Conversion
The roof slope is rebuilt at a near-vertical angle (72 degrees), maximising internal space. Creates the most room but involves the most structural work. Popular in London terraces.
- Cost: £50,000-£80,000
- Planning permission: almost always required (changes the roof shape significantly)
Planning Permission
Many loft conversions fall under permitted development, meaning no planning permission is needed. However, you will need to apply if:
- The additional volume exceeds 40 cubic metres (terraced/semi) or 50 cubic metres (detached)
- You want a front-facing dormer on a highway-facing elevation
- Your property is in a conservation area (restrictions on dormers and hip-to-gable)
- Your home is a listed building or a flat
- You want to raise the ridge height
Building Regulations
All loft conversions require building regulations approval. Key areas inspected:
- Structural design - floor joists, beams, load paths
- Fire safety - protected escape route (fire doors, intumescent strips), mains-wired smoke alarms on every floor
- Staircase - minimum headroom 2m, maximum pitch 42 degrees
- Insulation - walls, roof and floor must meet current thermal standards
- Sound insulation - between the loft and rooms below
- Windows - minimum opening area for fire escape
How Long Does a Loft Conversion Take?
- Velux conversion: 3-4 weeks
- Dormer conversion: 5-7 weeks
- Hip-to-gable: 6-8 weeks
- Mansard: 7-10 weeks
Add 2-4 months for design, planning (if needed), and building regulations before construction starts.
Does a Loft Conversion Add Value?
A well-executed loft conversion typically adds 15-20% to your property's value, often more than the cost of the work. Adding a bedroom with an en-suite bathroom delivers the best return on investment.
Getting Started
- Check your loft's suitability - minimum 2.2m head height at the ridge is ideal
- Appoint an architect or architectural technologist for a feasibility study
- Confirm whether you need planning permission
- Get building regulations drawings prepared
- Obtain 3 quotes from experienced loft conversion specialists
- Check party wall requirements if you share a wall with a neighbour