Types of Loft Conversion: Dormer, Hip-to-Gable and More

The main types of loft conversion compared

The four main types of loft conversion are the roof light, the dormer, the hip-to-gable and the mansard. A roof light leaves the shape of the roof as it is, and the other three change it to add space.

The costs in the table are averages for a 30m² loft on Checkatrade’s figures, and the build times come from Checkatrade’s timescale guide.

Type	What it is	The house it suits	Average cost, 30m² loft (Checkatrade cost guide)	Typical build time (Checkatrade timescale guide)
Roof light (Velux)	Windows fitted into the existing roof, with no structural change	A loft with enough room already; common on semis	£27,500	4 to 6 weeks
Dormer	A box structure with vertical windows, built out from a roof slope	Terraced houses, where it is the most common option, and semis	£50,000	10 to 12 weeks
Hip-to-gable	The sloping end of a hipped roof built up into a vertical gable wall	Semi-detached and detached houses with a hipped roof	£60,000	10 to 14 weeks
Mansard	One roof slope, typically at the rear, rebuilt almost vertical	Terraced houses	£65,000	12 to 16 weeks or more

A roof light conversion is usually the most affordable, and mansards tend to cost the most because of the major structural work. Build times also depend on the loft’s condition, its size and the finish, and a fully decorated room takes longer than a basic shell.

Roof light or Velux loft conversions

A roof light conversion, also called a Velux conversion, fits windows and ventilators into the existing roofline, with no structural alteration and no added floor space. That makes it the simplest type, suited to a loft that already has the room you need, and a 30m² roof light conversion costs £22,500 to £30,000 on Checkatrade’s figures.

Dormer loft conversions

A dormer is the most popular type of loft conversion, a box structure with vertical windows that adds headroom and floor space. A 30m² dormer conversion costs £40,000 to £60,000 on Checkatrade’s figures.

Rear, L-shaped and other dormer variants

Checkatrade describes five dormer variants, which differ in where the dormer sits and how much of the roof it covers.

• A rear dormer sits at the back of the house.
• An L-shaped dormer is built in two sections that form an L, often wrapping around the roof.
• A double dormer is two dormers on a pitched roof.
• A full-width dormer spans the full length of the roof, often with a wide window, and is more common on contemporary homes.
• A side dormer sits on the side of the property, often in a “dog-house” shape.

Hip-to-gable loft conversions

A hip-to-gable conversion extends the sloping end of a hipped roof into a vertical gable wall to add floor space, so the house needs a hipped roof to start with. Semi-detached houses often have one, and they tend to benefit most.

The job involves more structural work than a dormer, and a 30m² hip-to-gable conversion costs £50,000 to £70,000 on Checkatrade’s figures.

Mansard loft conversions

A mansard alters one roof slope, typically at the rear, to an almost vertical angle, and it is far more involved structurally than a full-width dormer. Most of that slope is replaced by a near-vertical wall and a flat roof, and a 30m² mansard costs £50,000 to £80,000 on Checkatrade’s figures.

Checkatrade says a mansard is likely to need planning permission. The application goes in before any work starts, and a decision on a large or complex project can take up to 13 weeks.

Shell and modular loft conversions

Modular and shell describe how the loft is built and how much of the work a company does, rather than the shape of the roof. In a modular conversion, much of the construction is done in advance, so the installation on site can be quicker and less disruptive, and it costs around £45,000 on Checkatrade’s figures.

A shell conversion covers the main structural work only, meaning the new floor structure, the roof alterations and a dormer if required, for around £30,000 on Checkatrade’s figures. The plastering, flooring and decoration are done separately, so when two quotes for the same type are far apart, check whether one of them is for a shell.

Which type of loft conversion is best for your house

Which type is best for your loft depends on the shape of the roof, how much space you need, the house and the budget. On Checkatrade’s figures, a conversion costs around £50,000 on a terraced or semi-detached house, around £62,500 on a detached house and around £75,000 on a bungalow.

Dormers are the most common option on a terraced house. On a semi-detached house, Velux and dormer conversions are common, and a hip-to-gable is often used to get the most space from the loft. Work through these before you ask anyone for a quote.

Getting quotes for the type you want

Among the Nottingham loft conversion companies ranked on memberships, guarantees and years in the trade, Top Mark Conversions builds rear dormer extensions and L-shaped dormer conversions, and Truss Developments’ projects include a hip-to-gable loft conversion in Beeston. Premier Roofing Solutions installs Velux roof windows with a 10-year Velux warranty, and Premium Home Conversions publishes starting prices for Velux, dormer, hip-to-gable and mansard conversions.

When you ask for a quote, name the type, the variant and where it goes, with the kind of house and the rooms you want, so every company prices the same conversion.