How Do Dormer Windows Add Space to a Room?

Written by f.r.r. mallory
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How Do Dormer Windows Add Space to a Room?
A dormer built into the roof of a home to provide extra light and usable space. (Chien-assis et Lauzes image by atmospheric from

A dormer is created when the sloped ceilings of an attic space are bumped out to form a vertical wall that can support a window. Typically, a dormer does not extend the footprint of the space but adds usable space by making the floor beneath the window accessible. Before a dormer is installed, the angle of the ceiling prevents full access to the floor space below it. Dormers add space in several ways.

Vertical Wall Space

Attic spaces are restricted by the shape of the roof. This often means that an attic space will only have floor to ceiling, vertical walls at the large gable ends of the house. A short wall is typically constructed 4 to 6 feet from the edge of the roof, to wall off the acute triangular space where the floor meets the roof line. This wall is called a knee wall and it may be only 3 or 4 feet tall. Small access doors can be installed in the knee wall to provide access for storage, and mechanical systems. When a dormer is installed, three new vertical walls expand the space in which you can walk.

How Do Dormer Windows Add Space to a Room?
An attic with a skylight provides light but no headroom or wall space. (retraite image by matteo NATALE from


To convert an attic space into liveable square footage that can be counted in the size of your home, the attic must have windows in each bedroom space that are large enough to provide escape, or egress, in the event of a fire. Because the size of egress windows is fairly wide, this forces attic dormers to be larger. The larger the dormer, the more usable floor and wall space is created. Larger windows also provide more light, which makes attic rooms feel more spacious.

How Do Dormer Windows Add Space to a Room?
This large dormer features an interior vaulted ceiling and expansive gable-shaped windows. (window image by anna karwowska from


Adding a dormer to an attic creates an opportunity to vault the ceiling of the dormer. In many new homes, dormers are designed to feature arched or angled windows above the egress windows to maximise the amount of light that the dormer is capable of producing. This design is usually paired with vaulting the main ceiling of the attic to create as much overhead space as possible.


Dormer windows are also used to create vaulted space over foyers, dining rooms and master bedrooms. In this situation, the dormer window is positioned in attic space but there is no attic floor. The walls of the dormer are merged with the walls of the room below to create a double-height room. This allows for the installation of large, dramatic chandeliers and brings additional natural light into the areas below.

How Do Dormer Windows Add Space to a Room?
Dramatic vaulted ceilings can be coupled to dormer windows. (Chandelier image by MAXFX from

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