A dormer is a structural element of a building that protrudes from the plane of a sloping roof surface. Dormers are used, either in original construction or as later additions, to create usable space in the roof of a building by adding headroom and usually also by enabling addition of windows.
Often conflated with the term "dormer", a dormer window is a window set into the dormer. Like skylights, dormer windows are a source of light and ventilation for top floors, but unlike skylights (which are parallel to the roof surface) they also increase the amount of headroom in the room and allow for more usable space.
A blind dormer or false dormer is a dormer that can only be seen from the outside of the house: it is roofed off on the inside, and does not provide any extra space or light. These are often used to make the house appear more impressive.
A dormer is often one of the primary elements of a loft conversion.
The main types of dormer are:
- Gable fronted dormer: Also called simply a gable dormer, the front of this dormer rises along a flat plane to a point at the ridge of the dormer roof. It is also known as a dog-house dormer (due to its visual similarity to same).
- Hip roof dormer: This style of dormer is an analogue to the hip roof— its roof is composed of three sloping planes which come together at the ridge of the dormer.
- Flat roof dormer: The roof of this dormer is flat and parallel to the ground with a frontal eave that parallels the main roof eave.
- Shed dormer: This dormer also has a flat roof but the roof slopes downward at an angle somewhat less than that of the surrounding roof. Its front eave line is, again, parallel to the main roof eave line. Shed dormers can provide more attic space and head room than gable dormers, but cannot be the same pitch as the main roof and may therefore require different roof sheeting. Often used in gable-roofed homes, a shed dormer has a single-planed roof, pitched at a shallower angle than the main roof.
- Wall dormer: This is a dormer whose face is coplanar with the face of the wall below, breaking the line at the cornice of the building.
- Eyebrow or eyelid dormer: "A low dormer on the slope of a roof. It has no sides, the roofing being carried over it in a wavy line."  The bottom of an eyebrow dormer is flat and the top is curved.
- Link Dormer: This is a large dormer that houses a chimney or joins one part of a roof to another.
- Bonnetted Dormer: This is 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: This is a complicated dormer structure composed of two gable dormers connected by a shed dormer.
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Improperly constructed dormers are prone to leaks and give rise to expensive repairs.
See also 
- Barr, Peter. "Illustrated Glossary - 19th Century Adrian Architecture". Sienaheights.edu. Retrieved June 17, 2009.
- Dictionary of Architecture & Construction, C.M.Harris.
- "Eyebrow". Buffaloah.com. Retrieved 2012-09-28.
- A Visual Dictionary of Architecture. Francis D.K. Ching
- Gitlin, Jane (2003). Capes: Design Ideas for Renovating, Remodeling, and Building New. Newtown, CT: Taunton. p. 44. ISBN 9781561584369.
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