Dormer, in architecture, a vertical window that projects from a sloping roof and usually illuminates a bedroom. The term derives from the Latin dormitorium, “sleeping room.” Dormers are set either on the face of the wall or high upon the roof, and their roofs may be gabled, hipped, flat, or with one slope. A small dormer in a roof or a spire is called a lucarne.

Simple dormers, frequently constructed in several rows, characterize the steep roofs of Teutonic countries. In the late Gothic and early Renaissance periods, more elaborate masonry dormers were designed that extended up from the wall line of the building and were richly decorated.

Some of the different types of dormer are:
GABLE FRONTED DORMER
Also called simply a gabled dormer, this is the most common type. It has a simple pitched roof of two sloping planes, supported by an outward face (any combination of glazed and unglazed materials). It thus includes a triangular section below the roofline, i.e. a gable. It is also known as a dog-house dormer (due to its similar shape).

HIP ROOF DORMER
Also called a hipped dormer, it has a roof composed of three sloping planes that rise from each side of the dormer frame and converge at the ridge—analogous to the hip roof.

FLAT ROOF DORMER
The roof of this dormer is a single flat plane approximately horizontal (although usually slightly inclined to allow rain water to run off).

SHED DORMER
This dormer also has a single flat plane roof, but in this case, it is sloped in the same direction as the principal roof, only at a shallower angle. A shed dormer can provide head room over a larger area than a gabled dormer, but as its roof pitch is shallower than the main roof, it may require a different roof covering.

WALL DORMER
As opposed to the dormer being set part way up the slope of the roof, this is a dormer whose face is coplanar with (shares the horizontal position of) the face of the wall below. This means that the face of the dormer is essentially a continuation of the wall above the level of the eaves.

EYEBROW, OR EYELID DORMER
A low and wide dormer with a curved roof and no sides. Instead, the roof covering is gradually curved up and over the dormer in a flattened bell curve.

LINK DORMER
This can be a dormer that houses a chimney or a dormer that joins one part of a roof to another.

BONNETED DORMER
An arched roof dormer, rounded in shape when viewed from front. Popular in Victorian homes, especially in certain areas, like the Southcott-style row-houses called Jellybean Row in St. John’s, Newfoundland.

NANTUCKET DORMER
A three-in-one dormer structure composed of two gable dormers connected by a shed dormer in between.

LUCARNE
A dormer on the slope of a Gothic spire, usually slender and gable fronted.

BLIND OR FALSE DORMER
A dormer that is only external; it provides no light and may provide no space internally. Often used to make the building appear more aesthetic.