What is a Transom in Architecture?

Instructor: Christopher Muscato

Chris has a master's degree in history and teaches at the University of Northern Colorado.

Every piece of a building has a technical name, and today we're going to check out the transom. We'll explore the function of this element, and see how it can look differently around the world.

Transom Defined

The more you learn about architecture, the more you come to realize that every piece of your home has a technical name. You're surrounded by more architectural features than you realize, and one of those pieces is the transom.

A transom is technically the horizontal structural beam that crosses over a door, and which specifically separates the doorframe from a window directly above it. It's just one more piece of architecture you've probably never really thought about, but now you'll start to realize is all around you.

Transom or Lintel?

The transom plays an important structural and aesthetic role in architecture, and to understand it we need to contextualize it within other elements of a doorframe. Your basic frame is built with one of the oldest construction techniques in human history, known as the post and lintel system. Basically, in this system you place two vertical sticks in the ground parallel to each other (the posts), and place a horizontal stick (the lintel) on top of them. Ta-da: the post and lintel. Obviously, complex architecture has a somewhat more refined approach to the post and lintel system, but the basic idea is the same.

So, what does this have to do with transoms? A transom is a beam of wood or stone or any other material that forms the upper crosspiece of a doorframe. This means that it is, structurally speaking, a type of lintel. Transoms can be lintels if they provide structural support to the doorframe, but are all lintels transoms? No. What differentiates the transom from other types of lintels is the existence of a window above it. The transom structurally and aesthetically separates the doorframe from this window. It therefore provides strength and support to both the doorframe and window frame. That's its true purpose, and the main defining feature of this architectural element.

See the beam above the doorway but below the window? That is the transom.

The Transom Window

In North America, the term transom is often used to both describe the lintel that separates the doorframe and window, as well as the window itself. Technically, this window is known as the transom light, or sometimes the transom window in the United States. North American transom lights tend to be rectangular, divided into geometric sections by vertical dividers.

In Europe, however, transom lights are very often semi-circular. With dividers fanning out from the center of the arch-shaped feature, it creates the impression of a glass folding fan. For that reason, European transom lights are often referred to as fanlights.

Fanlights in Russia

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