Dormers are named for where they sit and what shape their roof takes, and the choice is rarely free. The rear of a house is the least visible and the least constrained, full width dormers buy the most room and look the heaviest, and a hipped roof has to be changed before it can take much at all. Each shape trades appearance against usable floor.
Rear dormer loft conversion: why almost everyone builds one
A dormer on the rear roof slope is the default because it is the least visible from the street and, on many houses, can fall within permitted development where a front dormer cannot. It also usually faces the garden, which is where people want the window. The rear slope is often the larger one on a house that has been extended, so it is the slope with the most to give.
Full width dormer loft conversion against a modest box
A full width dormer runs the length of the rear slope and produces the most usable floor of any option. It is also the most visible change to the building and the one most likely to attract a planning objection or an article 4 restriction, and on some streets it reads as a flat wall where a roof used to be. A smaller box set within the slope, with roof left around it, keeps more of the original shape and less of the room.
L shaped dormer loft conversion and back additions
Many Victorian and Edwardian terraces have a back addition running off the main roof. An L shaped dormer builds into both the main rear slope and the addition, turning the corner and producing considerably more space than either alone. It is more complex to build and to weather, because the two roofs meet at a valley, and that junction is where these conversions leak if the detailing is poor.
Hipped roofs and the gable end
A hipped roof slopes on all sides, so there is no vertical gable wall and very little usable volume at the ends. The usual answer is a hip to gable conversion, which rebuilds the hipped end as a vertical gable and then adds a dormer to the rear. It is a bigger structural job than a plain dormer because it changes the roof form, and it changes the look of the house from the side.
Pitched dormer loft conversion or a flat roof one
A flat roofed dormer is cheaper, gives the most internal height for its size and is what most rear dormers use. A pitched roof dormer sits better on a period house and reads as part of the roof rather than an addition, at the cost of head height at the edges and more money. Where the dormer is visible from the street the pitched version is often what gets consent.
Questions people ask about rear dormer
Which dormer gives the most space?
A full width dormer on the rear slope, and an L shaped one where there is a back addition to build into. Both are the most visible and the most likely to need planning permission, so the extra floor is bought with elevation and process.
Can I put a dormer on the front of the house?
Sometimes, but a dormer on the principal elevation facing a highway is normally outside permitted development and needs planning permission. Whether it is granted depends on the street and the local policy.
What is hip to gable and do I need it?
It rebuilds a sloping hipped roof end as a vertical gable wall, creating volume where there was almost none. You need it if your roof is hipped and you want a usable room rather than a cupboard at that end.
Is a small dormer loft conversion worth doing?
If it is placed where the staircase arrives and where you need standing height, a small dormer can make the difference between a room and a loft. Placement matters more than size for usability, though not for floor area.
Does a flat roof dormer loft conversion cost less than a pitched one?
Generally yes, because there is more structure, more covering and more detailing for the same internal space. They are often specified where appearance or a planning condition requires them.