Owning a Property

Loft Conversion Types, Dormer, Hip-to-Gable, Mansard and L-Shaped Compared

Choosing the right loft conversion type depends on your roof structure, budget, and how much space you need. This guide compares the four main types and explains the planning implications of each.

Published: 16 Mar 2026 · Updated: 16 Mar 2026 · 6 min read

#HomeOwner#PropertyOwner#LoftConversion#HomeImprovement#Planning#PropertyPassportUK

Why Loft Conversion Type Matters

The type of loft conversion best suited to your home depends on three things: the existing roof structure (whether it is a traditional cut rafter roof or a modern trussed rafter roof), the amount of usable space you need, and the planning constraints that apply to your property.

All loft conversions must comply with Building Regulations regardless of whether planning permission is required, and a structural engineer must assess the roof and floor loadings.

Velux (Rooflight) Conversion

The simplest and least expensive type. Velux-style rooflights are inserted flush into the existing roof slope, the roof shape is not altered. This is almost always Permitted Development, even in conservation areas (with restrictions on front-facing rooflights).

Best suited to roofs with sufficient existing head height (typically 2.2 metres or more from floor to ridge).

Dormer Conversion

A dormer is a box-shaped vertical extension that projects from the roof slope, creating additional floor area and full-height head room. Rear dormers are the most common type of loft conversion in England.

Rear dormers on non-principal elevations are generally Permitted Development for houses (not flats), subject to the 40 or 50 cubic metre volume limit. Front dormers (on the principal elevation facing the street) always require planning permission.

Hip-to-Gable Conversion

Applicable only to properties with a hipped roof (where the roof slopes on all four sides). The hip end of the roof is replaced with a vertical gable wall, creating a larger, square loft space.

Hip-to-gable conversions are Permitted Development on detached and semi-detached houses in most areas, subject to volume limits. They require planning permission in conservation areas and for listed buildings.

Mansard Conversion

A mansard conversion involves replacing a large portion of the roof with near-vertical walls (typically at 72 degrees) and a shallow pitched roof on top. This maximises the internal space significantly and gives a distinctive urban aesthetic.

Mansard conversions almost always require planning permission because the change to the roof line is substantial. They are most common on terraced Victorian or Edwardian houses in cities.

L-Shaped Conversion

An L-shaped conversion combines a main rear dormer with a smaller dormer over a rear outrigger (the rear extension typical of Victorian terraced houses). This creates a large, well-proportioned loft room.

Conversion type	Planning permission usually needed?	Typical cost range	Space created
Velux (rooflight)	No (PD)	£15,000–£25,000	Minimal increase
Rear dormer	No (PD, rear only)	£30,000–£50,000	Moderate
Hip-to-gable	No (PD, most cases)	£35,000–£55,000	Good
Mansard	Yes	£45,000–£70,000+	Excellent
L-shaped	Usually no (PD)	£40,000–£65,000	Excellent

Cost ranges are indicative only and vary significantly by location, specification, and contractor.

Building Regulations Requirements

Every loft conversion, regardless of type or planning status, must comply with Building Regulations. Key requirements include:

**Structural**, Floor joists must be strengthened; roof structure assessed
**Fire safety**, Mains-wired interlinked smoke alarms; fire-resisting construction to the new floor and staircase enclosure; 30-minute fire doors to rooms off the new staircase
**Stairs**, A fixed staircase (not a loft ladder) at no more than 42 degrees pitch
**Thermal insulation**, To meet Part L energy efficiency requirements
**Means of escape**, Window in each habitable room (minimum 0.33 m² and 450 mm in both dimensions, maximum 1.1 m from floor level)

Once Building Regulations approval is granted, store your completion certificate on Property Passport UK, buyers and mortgage lenders will require it when you sell.