Dormer, hip-to-gable or rooflight: which loft conversion suits your house?

By James Reilly, Swanbourne Construction Ltd · Published 15 October 2026 · Planning and Building Regulations points checked October 2026

The type of loft conversion that suits your house is mostly decided by the shape of the roof. A rooflight conversion keeps the roof as it is and only works where there is already plenty of height. A rear dormer — a box built out of the back slope with vertical walls — suits most terraces and semis and is the commonest type. A hip-to-gable rebuilds the sloping end of a hipped roof as a vertical wall, which is why it suits 1930s semis, detached houses and many bungalows, usually combined with a rear dormer. A mansard or roof lift creates the most space, costs the most, and almost always needs planning permission.

Most people come to us having already chosen a type from a magazine. That is a reasonable starting point and frequently the wrong answer, because the right type for your house is decided by things you can check yourself in ten minutes in the loft. This guide shows you what to look for.

The types at a glance

Price bands from our price guide, revised August 2026. More on what moves them in loft conversion costs in Bognor Regis.

Rooflight conversion

New rooflights go into the existing slope, a floor goes in, insulation and a staircase follow, and the roof shape does not change. It is the cheapest and quickest type, with the least disruption and the simplest planning — rooflights that project no more than 150mm from the slope are usually permitted development, and that right is not switched off in conservation areas the way dormer rights are.

The catch is that it adds no headroom. The usable floor is the strip down the middle where you can stand, and the room is only as good as the roof it is in. It works on steeper, taller roofs, particularly older cut roofs with a good pitch. On a shallow or trussed roof it rarely gives a room worth having.

Rear dormer

A dormer is a box built out of the roof slope, with vertical walls — the "cheeks" — and a flat or shallow roof, so the floor under it has full headroom. A full-width rear dormer on a terrace or semi can turn a loft into a double bedroom and an en-suite. It is the commonest type for good reason: it suits the widest range of houses and usually stays within permitted development.

Dormers can be clad, tile-hung or rendered. Cladding keeps the weight and the depth of the cheeks down, which is why the finished dormer at Whyke Close in Chichester is in dark grey boarding. Permitted development requires materials "similar in appearance" to the house, so check what that means for yours before choosing.

L-shaped dormer

On a Victorian or Edwardian terrace with a two-storey rear wing — the "outrigger" — two dormers can be joined in an L, one on the main roof and one over the wing. It typically gives a bedroom on the main roof and an en-suite over the back addition. It is more complex and uses more of the permitted development volume, but on the right house it produces the most usable floor space short of a mansard. These houses are more common in Chichester and Littlehampton than in Bognor's post-war streets.

Hip-to-gable

A hipped roof slopes in from three or four sides. That is the shape that makes a loft look impossible from the ground, because the usable floor is a narrow strip down the middle and the ceiling falls away before you reach either end. A hip-to-gable takes the sloping end off and builds a vertical gable wall up to the ridge in its place, so the end of the room becomes a full-height wall you can put furniture against.

It is the standard answer for 1930s hipped semis, hipped detached houses and many bungalows. On its own it often gives enough for a room; combined with a rear dormer it can give a large bedroom and a bathroom. It does not work on a mid-terrace, which has no hip.

The hip-to-gable we built in Guildford hung the new gable in plain clay tiles to match the roof, so from the street the new end of the house reads as part of the old one. Rendering or boarding would have been quicker. It would also have looked like an addition.

Mansard

A mansard rebuilds one or both slopes of the roof almost vertically, with a near-flat top. It effectively adds a whole storey and gives the most space of any loft conversion. It is common on London terraces and much less so on the West Sussex coast. Because of its volume and the way it replaces the eaves, it almost always falls outside permitted development and needs a planning application. It is the most expensive type to build.

Roof lift

Where the roof is too low to convert at all, the whole roof can be taken off and rebuilt higher or steeper. It is the most effective and the most expensive option, and loft (Class B) permitted development does not allow anything higher than the existing roof, so it normally needs planning permission. There is one exception: houses built between 1 July 1948 and 28 October 2018 can add storeys under a permitted development right (Class AA) through prior approval rather than a full application — up to two storeys on a house, one on a bungalow — but not in a conservation area, the National Park or a National Landscape, and the council still judges the design, the neighbours' amenity and the effect on the street. On a bungalow it shades into adding a full first floor, which is a different conversation entirely.

Which suits your house?

Around Bognor Regis, Felpham, Pagham and Rustington, a great deal of the housing is 1950s and 1960s bungalows and post-war semis, which is why so much of our loft work is hip-to-gable and rear dormer. In central Chichester and Arundel, conservation areas push more jobs towards rooflights or carefully designed dormers with a planning application.

How to check your head height

Go into the loft with a tape measure. Measure from the top of the ceiling joists — the timbers you would be standing on — to the underside of the ridge timber at the highest point. Around 2.2m is the figure the trade uses as a comfortable starting point.

That 2.2m is a rule of thumb, not a regulation. Approved Document K, which governs stairs, contains no minimum room height. What it fixes is the headroom over the stair: 2m normally, reduced for loft conversions to 1.9m at the centre of the flight and 1.8m at the side. Some 2026 guides wrongly say the regulations require 1.9m in occupied rooms; 1.9m is the stair figure only.

Why does 2.2m matter in practice? Because the finished room loses height. A new floor goes in on top of or beside the old ceiling joists, which were never sized to be a floor. Then there are floorboards, and insulation to the current standard in the roof — enough to make a real difference to the finished height. A loft that measures 2.2m bare ends up noticeably lower. If yours is short, a dormer or hip-to-gable creates full-height floor where there was none, and in rare cases ceilings below can be lowered, as at Whyke Close. Our older article on which lofts cannot be converted goes into the exceptions.

Cut roof or trussed roof?

While you are up there, look at the timbers. A cut roof has rafters, horizontal purlins part-way up, and struts down to internal walls, with open space in the middle. A trussed roof — most houses built from around the 1970s — has a W-shaped web of timber in every truss, closely spaced. Every member of a truss is doing structural work. None can simply be cut out, so a trussed roof needs a new designed structure before it holds a room, which is a big part of why trussed lofts cost more to convert.

Questions people ask about types of loft conversion

Where these facts come from

• Approved Document K: stairs and headroom.
• GPDO 2015, Class B and Class C.
• Homebuilding & Renovating: types of loft conversion (December 2025).
• Homebuilding & Renovating: loft conversions for low roofs (June 2025).