The Difference Between a Dormer and a Roof Window

Roof Windows

• Roof windows are just what they sound like -- windows embedded in a roof. These windows resemble skylights. However, roof windows open whereas skylights provide only a glass surface laid into a roof. Roof windows usually open outward, providing light and ventilation in attic spaces. Any such window qualifies as a roof window, irrespective of size or the shape of a roof. For instance, a 1-by-1-foot window on a flat roof qualifies as a roof window, as does a 4-by-4-foot window on a sloped roof.

Dormer

• Dormers are vertical architectural structures containing windows. They protrude from sloped roofs. These structures add light and ventilation to attic spaces or bedrooms in the same manner as roof windows. Dormers also add space to attics by extending beyond the line of a roof. Various types of dormers exist, including eyebrow, gable, hipped, inset and shed. The shape of a dormer and the manner in which it protrudes from a roof define it. Gable and inset dormers, for instance, are both rectangular although a gable dormer sticks straight up from a roof whereas an inset dormer nestles into the roof.

Architectural Differences

• Architectural differences most obviously differentiate roof windows from dormers. Roof windows constitute nothing more than windows. Dormers comprise an architectural structure that includes a window but also consists of walls and a roof. While dormers qualify as separate entities that rise away from roofs, roof windows constitute part of a roof’s surface, on a level plane with the rest of the roof. Roof windows provide largely functional qualities while dormers provide functional and aesthetic qualities.

Other Differences

• Roof windows can exist on any type of roof -- as long as a window sits on a roof and opens, it qualifies as a roof window. Dormers only arise from sloped roofs. Different terms exist for describing structures arising from flat roofs. Also, multiple types of dormers exist, with terms to describe their differing natures. Roof windows, on the other hand, are all referred to as "roof windows," irrespective of any variation in form. Furthermore, whereas roof windows only provide light and ventilation, dormers actually increase the available space in an attic or other space.