A transom window (also called a fanlight; Dutch: bovenlicht) is a window or glass panel positioned above a door or another window to admit additional daylight into a room. It is separated from the door or lower window by a horizontal bar called the transom.
Types of transom windows
Transom windows come in several forms:
- Fixed transom — a non-opening glass panel that serves purely to let in light. This is the most common type above front doors.
- Operable transom — a hinged or pivoting panel that can be opened for ventilation. Often top-hinged, allowing it to tilt outward.
- Decorative fanlight — a semi-circular or arched transom, typically found above the entrance doors of Georgian and Victorian buildings. These often feature ornamental glazing bars in a fan pattern, giving the fanlight its name.
- Internal transom — a glass panel above an interior door, used to borrow light from an adjacent room or hallway.
Benefits
Transom windows offer several practical advantages. They increase the amount of natural light entering a space without enlarging the door or window below. In older buildings with high ceilings, they fill the gap between the top of the door and the ceiling line, improving both aesthetics and illumination. When operable, they provide ventilation while the door remains closed and locked, which is useful for security.
Application in construction
In new construction, transom windows are typically integrated into the door or window frame as a single unit. The head rail of the lower frame doubles as the sill of the transom. In renovation projects, adding a transom window above an existing door requires raising or modifying the lintel, which may need structural approval.
Transom windows must meet the same thermal performance and safety glazing standards as other windows in the building envelope.
Related terms
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