Final answer:
The short lengths of 2x material above door and window openings are called headers. They distribute structural loads and are crucial in buildings. Architectural details like clerestory windows, Chicago windows, and mullions may enhance the functionality and appearance.
Step-by-step explanation:
The short lengths of 2x material used above door openings and above or under window openings are called headers. Headers are structural elements used in construction to distribute the load from the roof, upper floors, or other overhead pressure down to the surrounding frame rather than directly over the openings. They ensure that doorways and windows do not bear direct structural loads which could lead to deformation or failure.
In the context of windows, it's also important to consider various window designs that exist in architecture, such as clerestory windows that allow light and air into tall buildings, or the Chicago window, which consists of a fixed center panel flanked by operable double-hung sash windows. Moreover, builders might include aesthetic details, such as bundled colonettes, which make the masonry around the windows appear more delicate and serve as mullions to separate the panes of glass.