Dormer Windows: Definition & Styles

Instructor: Christopher Muscato

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

There are many ways to add on to an existing house. In this lesson, we'll look at dormer windows and see how these structures can be used to increase living space inside a home.

Dormer Windows Definition

Houses tend to evolve over time. The family grows bigger, someone comes into some money, or someone loses money and has to rent out the basement. For countless reasons, people have expanded, added on to, and remolded their houses for generations upon generations. As a result, your typical four-sided structure starts to take on a more distinctive look.

One common feature of modern houses, which likely began as a common way to expand upon existing homes, is the dormer window, often just called a dormer. A dormer is a window that projects vertically from a sloping roof. It is not set into the roof at an angle but instead set out from it, making this a unique and distinctive part of many modern homes.

Building with dormers in the roof

History of Dormer Windows

The term ''dormer'' actually stems from the Middle French word dormir, which means ''to sleep.'' That tells us something about how this window was being used: it was used to bring light into bedrooms built into the attic. In fact, the first systematic use of it dates from 17th-century French architect Francois Mansart, who placed rows of vertical windows into sloping roofs so that the attics could be converted into bedrooms. See? The structure of many buildings reflects the change in use over time.

While Monsieur Mansart may receive credit for developing the dormer as we know it today, it's almost certain that he wasn't the first to do so. Northern European countries had long built up wooden, domestic architectural styles for centuries before this. These homes featured long, steeply sloping roofs, some of which stretched all the way to the ground. Many of them had windows set into them, making them early versions of the modern dormer. Regardless of its precise origin, however, the dormer window became a common way to make the uppermost floor of a home habitable and fit for comfortable living.

Styles and Types of Dormer Windows

There are basically as many styles of dormer windows as there are styles of roofs, but in general, we can organize them into five basic categories. Each one is defined not by the window itself, but by the type of roof covering it and the relationship between the main roof of the house and this little, box-like window structure.

First is the gable style dormer. A gable dormer is covered with two sloping sides of a roof, which meet in the middle and are open in the direction of the window. So, it's exactly the same setup as the gabled roof of a house, and gabled houses generally have gabled dormers.

Since the dormer itself is perpendicular to the roof, the gabled dormer is perpendicular to the gabled house roof. For that reason, some people with a gabled house prefer to have shed style dormers. A shed dormer has a roof that slopes in the same direction as the main roof.

Two gable dormers underneath a shed dormer

But what if your house doesn't have a gabled roof? What if it has a hipped roof, which slopes in all four directions of the house? For a house with a hipped roof, many recommend a hipped dormer, which projects from the roof but also has its own roof sloping down in each available direction. This can make the dormer look sort of like its own miniature house, which a lot of people enjoy.

Of course, a rectilinear dormer isn't for everyone. A dormer which still projects from the roof as a rectilinear structure may have an arched or curved roof, which we call the segmental style. This is popular in many fancy homes and adds some fun decorative curves to the house.

Segmental dormers

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