transoms

Transom refers to a crosspiece or crossbar in architecture that runs horizontally across a doorway or window. It most commonly denotes the horizontal element above a door that divides the door from the window or from the upper opening, and it is the part where a transom light may be installed. When a window sits above a door, the window is typically called a transom window or a transom light. Transoms can be fixed or operable, allowing light into interiors or enabling ventilation without opening the main door. They may be conceptual as a structural support as well, helping to transfer loads around the opening. In traditional and restrained-modern architecture, transoms are often aligned with lintels and mullions and can be plain or richly decorative.

In terms of construction and materials, transoms are made from timber, steel, aluminum, or PVC, and glazed transoms may contain single or double glazing or translucent panels. Their size varies with the door height and architectural style. In maritime usage, the term transom also refers to the flat transverse surface forming the stern of a boat or ship, a design feature that defines hull shape and may support equipment or mounting plates.

Related terms include lintel (the horizontal bearing piece above a doorway), mullion and transom light (the window divided by a horizontal bar), and the concept of a door transom or transom window in various architectural styles.