Flat Roof, Gable, Hip to Gable and L Shaped Dormers

Flat roof dormer

The workhorse. A box with vertical walls and a flat roof, usually run across most of the rear slope. It gains the most internal volume for the least money, because every part of it is full height and nothing is lost to a pitch.

Its weakness is appearance. A full width flat roof dormer on a modest roof can look like a bolt on if the cheeks are clumsy or the window proportions are wrong. Set the face back from the eaves, keep the cheeks slim and clad them well, and the same box reads as considered.

Gable fronted dormer

A dormer with a pitched roof and a small triangular gable at the front. It matches traditional roofs far better and is the usual answer where appearance matters, including anything visible from a street of period houses.

You pay for it in volume. The pitched roof pulls the ceiling down at the front, so a gable dormer of the same width gives less usable floor than a flat roof one. On period property it is often still the right call.

Hip to gable

Strictly this is not a dormer at all, it is a change to the main roof, but it is the necessary first move on any house with a hipped end, meaning a roof that slopes on three or four sides rather than ending in a vertical wall.

Extending the hipped side up into a vertical gable turns a pinched triangular loft into a rectangular one, and the resulting space is usually then combined with a rear dormer. Semi detached and detached houses from the 1930s to the 1960s are the classic candidates.

Only possible where the hip is yours to alter, not shared · Involves rebuilding the gable wall in masonry and reforming the roof · Usually adds a week or so to the programme · Frequently transforms an unviable loft into a straightforward one

L shaped dormer

Where a house has a rear outrigger, the back addition running off the main block that is common on Victorian and Edwardian terraces, two dormers can be joined into an L. One runs across the main rear slope, the other along the outrigger.

This is the largest of the options and typically yields two bedrooms and a bathroom rather than one bedroom. It is also the most involved structurally, because the two roofs meet at a valley that has to be reformed.

Choosing between them

Work from the roof outwards rather than from the wish list inwards. Hipped roof means hip to gable comes first. Outrigger present and space needed means L shaped. Rear slope only and maximum space wanted means flat roof. Visible from the street or period context means gable fronted, and accept the smaller room.

Frequently asked questions

Which dormer type gives the most space?

The L shaped, then the full width flat roof, then hip to gable combined with a rear dormer, then the gable fronted. The order is essentially inverse to how traditional each one looks.

Can I have a dormer on the front of the house?

Sometimes, but front facing dormers fall outside permitted development on the principal elevation, so a planning application is required and design scrutiny is much closer.

Does a hip to gable need planning permission?

Often it falls under permitted development on a house, subject to volume limits and the property not being in a protected area, but it is one to confirm with the local planning authority rather than assume.

What are dormer cheeks clad in?

Tile hanging, slate, standing seam metal, or fibre cement board are all common. Matching the main roof covering usually reads best on period property, while metal suits a crisp modern box.