Dormer
A dormer is a structure that projects from a sloped roof, with its own window and roof. It adds light, ventilation and headroom to the space directly under the roof, such as an attic room or upper story.
Common types include the gable dormer with a small peaked roof, the shed dormer with a single roof plane sloping more gently than the main roof, and the hipped dormer. Shed dormers can run most of the length of a roof and turn a cramped attic into a full-height floor.
Dormers matter for square footage because they raise the ceiling over part of the floor. Under the usual rules, finished space with a ceiling below 5 feet is excluded and the room needs at least 7 feet over half its area. See finished attic GLA rules.
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