A door transom is the horizontal cross member in a door frame that separates the door leaf from a fanlight or solid panel above. It serves both as the top of the door opening and as the sill of the fanlight. The same component in a window frame is also called a transom; in a door frame the more specific term *door transom* is used.
Function
The door transom carries several functions at once:
- Structural — it stiffens the frame and holds the jambs at a fixed distance
- Functional — it forms the head of the opening against which the door closes
- Aesthetic — it gives a clear compositional split between door and fanlight
- Building physics — in insulated frames it forms the boundary between two openings in the facade
Construction
A door transom is usually made of the same material as the rest of the frame and is connected with mortise-and-tenon or modern corner joints:
- Timber — meranti, pine or oak; in heritage joinery often with a special moulded profile
- PVC — reinforced with a steel core
- Aluminium — especially in larger curtain wall units
- Steel — in steel frames in industrial buildings and older townhouses
The transom has an overlap or stop bead on the underside for the door to close against, and a rebate on the upper side to receive the fanlight or solid panel.
When it is used
A door transom is used wherever a door frame does not reach the ceiling and the space above the door is filled with:
- A fixed fanlight — to bring extra daylight into halls and corridors
- An opening fanlight (hopper) — for ventilation
- A solid panel — in heritage buildings or where no light or ventilation is needed
- A signboard or house number — common in older facades
In renovations the transom is sometimes removed so a taller door can be fitted, provided the frame still works structurally.
Vocabulary check
| Component | Position | Function |
|---|---|---|
| Head jamb | Top of the frame | Top closure of the frame |
| Door transom | Between door and fanlight | Horizontal divider |
| Sill / threshold | Bottom of the frame | Floor closure of the door |
| Jamb | Vertical | Side of the opening |
| Muntin | In a window | Subdivision of glass panes |
Related terms
- Transom
- Door frame
- Head jamb
- Fanlight
- Door
- Jamb
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