Velux and dormer conversions are the two most popular types of loft conversion in the UK, and for good reason. Both can transform unused roof space into a functional room, but they differ significantly in cost, space, appearance, and suitability. Choosing the right one depends on your property, your budget, and what you want to use the space for.
Here's a detailed comparison to help you decide which is right for your home.
What Is a Velux Loft Conversion?
A Velux conversion (also called a rooflight conversion) is the simplest type. It works within the existing roof structure, adding high-quality roof windows for natural light and ventilation. The roofline stays unchanged, and no external walls are built.
This makes it the fastest and least disruptive conversion to carry out, often completing in three to four weeks.
Pros of Velux Conversions
- Lower cost -- Typically £15,000 to £25,000, making it the most budget-friendly option. See our full cost breakdown for 2026.
- No planning permission needed -- Almost always falls under permitted development rights.
- Minimal disruption -- No scaffolding towers or extended building work on the exterior.
- Quick build time -- Three to four weeks on average.
- Natural aesthetic -- Roof windows flood the space with light without altering the look of your home.
Cons of Velux Conversions
- Limited headroom -- You're restricted by the existing roof pitch. Low eaves reduce usable floor area.
- Less floor space -- No additional structure means less room compared to a dormer.
- Not suitable for all roofs -- Shallow roof pitches or low ridge heights may not provide enough standing room.
What Is a Dormer Loft Conversion?
A dormer conversion extends outward from the existing roof slope, creating a box-like structure with vertical walls and a flat or pitched roof. This significantly increases headroom and usable floor space.
Rear dormers are the most common configuration, though side dormers and front dormers are also possible depending on the property and local planning context.
Pros of Dormer Conversions
- Maximum usable space -- Vertical walls provide full standing height across a much larger area.
- Room for an en-suite -- The extra space makes it practical to include a bathroom.
- Usually permitted development -- Most rear dormers on houses fall within permitted development rights, though there are volume limits.
- Suits more property types -- Works well on semi-detached and terraced homes where roof height may be marginal.
- Higher property value increase -- The additional usable space typically adds more value at resale.
Cons of Dormer Conversions
- Higher cost -- Typically £30,000 to £55,000, reflecting the additional structural work.
- Longer build time -- Usually six to eight weeks.
- More disruptive -- Requires scaffolding and external construction work.
- Visual impact -- A poorly designed dormer can look out of place. Good design is essential.
Side-by-Side Comparison
| Feature | Velux | Dormer |
|---|---|---|
| Cost | £15,000 - £25,000 | £30,000 - £55,000 |
| Build time | 3-4 weeks | 6-8 weeks |
| Usable floor space | Moderate | Large |
| Head height | Limited by roof pitch | Full height across most of room |
| Planning permission | Rarely needed | Usually permitted development |
| Disruption | Low | Moderate |
| En-suite possible | Difficult in most cases | Yes, comfortably |
| Property value added | 10-15% | 15-20% |
Which Properties Suit Each Type?
Velux conversions work best for:
- Properties with a steep roof pitch (40 degrees or more) and a ridge height of at least 2.4 metres from the top of the ceiling joists
- Homeowners wanting a home office, spare bedroom, or playroom on a smaller budget
- Listed buildings or conservation areas where external alterations are restricted
- Bungalows with suitable roof geometry
Dormer conversions work best for:
- Semi-detached and terraced houses where a Velux alone wouldn't provide enough space
- Homeowners who want a master bedroom with en-suite
- Properties with lower roof pitches that need the extra headroom a dormer provides
- Families needing to maximise every square metre of living space
Planning Permission Considerations
Most Velux and rear dormer conversions on houses fall within permitted development rights, meaning you won't need planning permission. However, there are important conditions:
- The volume added must not exceed 40 cubic metres for terraced houses or 50 cubic metres for detached and semi-detached houses.
- Materials must be similar in appearance to the existing house.
- No extension can be higher than the existing roofline.
- Side-facing windows must be obscure-glazed and non-opening below 1.7 metres.
Flats, maisonettes, and properties in conservation areas or Article 4 direction areas may have different rules. Always check with your local planning authority before starting work.
Making the Right Choice
The best conversion type for your home depends on your roof structure, your budget, and what you want to achieve. If you're unsure, a professional survey is the quickest way to get clarity.
At Better Lofts, we carry out free loft assessments for homeowners across the South Coast. We'll measure your existing space, discuss your options honestly, and recommend the conversion type that delivers the best result for your property and budget.
Book your free survey today or browse our loft conversion services to explore what's possible.
