A dormer is a framed structure that projects from a roof. Dormers come in many shapes and sizes They may have pitched or flat roofs, sides called "dormer cheeks" and a vertically placed window or other opening at the front. Dormers often have a gable or pediment over the window called the "dormer head." Other common dormer styles include arched, deck, eyebrow, flat, hipped, inset, shed or combinations ("composite").
Sometimes dormers are placed flush with a wall plane, between a roof and the wall of a building, with the cornice line running through them. Called wall dormers, these are considered wall, rather than roof, elements and are less common than roof dormers. Another dormer-like element is a roof louver designed as a dormer. Although they allow air flow into an attic, they are actually more of a roof vent than a true dormer.
The development of the dormer is attributed to French architect Francois Mansart (1598-1666). He created the highly recognizable Mansard-style roof, characterized by four steep sides. The deep pitch of these roofs resulted in tall attic spaces that could be used for additional sleeping areas without violating the existing building height restrictions in Paris. Mansart inserted windows into these sloping roofs in the form of dormers, which added space and light.
Flanking means placing something on either side of something else or along one side. In an architectural context, dormers placed on either side of a central element, such as a larger central dormer, are flanking dormers.
A pediment is a low pitched triangular gable over a porch, door or window. In ancient Greece and Rome, civic buildings often had a row of columns placed across their portico (porch) or entry area. Above these columns ran a horizontal beam, topped by a triangular, vertical wall, called a pediment. Over the pediment was the building roof peak. Pediments may be monumental, such as a pediment that extends across the entire front of a building facade. Pediments may be small, such as those used over doorways, niches or windows. Triangular pediments are common, but other kinds include broken, broken-apex (also called open or open-topped); broken base (or open-bed); and a variety of scrolled pediments.
Pedimented flanking dormers are windows that project from an attic to bring in air and light and create a comfortable living area. They are often arranged adjacent to a central dormer and have a triangular pediment over them with decorative molding that simulates columns.