By Glenda Taylor and Bob Vila | Updated May 17, 2022 5:03 PM

Located on the sloped side of a roof, a dormer window brings natural light into an attic, loft, or any room with a vaulted ceiling. This type of window sits vertically in a framed structure that juts outward from the pitch of the main roof and features a little roof of its own above the window. Dormer windows are often associated with Colonial, Greek Revival, and cottage-style architecture, but they can be found on virtually any style of house that has a sloped roof.

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If you’re considering dormer windows for a new house construction or loft conversion, keep reading. We’ll explain the pros and cons and advise on the style options available.

Dormer windows first appeared in residential roofs in 16th Century Britain, where they were used to direct natural light into attic sleeping areas. The word “dormer” comes from the French “dormeor,” which means “sleeping room.”

Dormers have an even earlier predecessor, however: an architectural feature called a “lucarne” that first appeared the 12th Century Europe. Lucarnes—tall, narrow roofed projections—were often found on the tall spires of Gothic Cathedrals. They were designed to promote fresh airflow through the tops of the spires, which could get quite hot during summer months. A good example of Gothic lucarne architecture still exists on the Christ Church Cathedral in Oxford. While the lucarnes of old didn’t have glass windows, tall narrow dormer windows today are sometimes called “lucarne dormers.”

In residential construction, the use of dormer windows hasn’t changed much over the last few hundred years. They’re still valuable for bringing light into attics and lofts, but today, homeowners are more interested in choosing a style of dormer window to complement their house design.

The style of a dormer window is defined by the style of the roof above the window. The following dormer window styles are commonly found on today’s homes:

Often, a dormer roof matches the style of the house’s main roof, but there are plenty of exceptions. A house with a gable roof can have a gambrel dormer, a shed dormer, or another style, depending on architectural preference. The type of roofing material on a dormer window typically matches the roofing material on the main roof. If the main roof has asphalt shingles, for example, the roof over the dormer window likely will as well.

Dormer windows are desirable not just for bringing in natural light but also for their exterior aesthetic appeal. If you’re considering adding dormer windows to a new house or having one retrofitted on your existing home, the following benefits and drawbacks might help in the decision-making process.

If you’re having a new home built, the framing contractor will construct the frame of the dormer at the same time the roof structure is framed. Sheathing (the plywood that covers the framing studs) is attached to the outside dormer walls and over the rafters of the main roof at the same time. The next step is the installation of a vapor barrier wrap over the sheathing on the vertical walls of the dormer. The window is usually installed next, and then the roofing contractor will install the shingles over the dormer roof and the main roof at the same time so there is no visible transition between the two—just a seamless layer of shingles over the entire roof. When the exterior is complete, the interior of the dormer is finished (painted and trimmed) at the same time the interior loft space is finished.

When you’re having a dormer window retrofitted in an existing house, the main focus is to reduce the amount of time you have a gaping hole in your roof. For this reason, interior framing, such as alterations to the interior rafters or trusses (alterations that must be cleared by a structural engineer), is often done first, and then the contractor constructs the exterior frame of the dormer on the surface of the roof. When that’s complete, the connecting hole is cut through the roof and then any necessary additional framing takes place. The window is typically installed next and then the dormer can be wrapped with a vapor barrier and the exterior and interior can be finished as desired.

If you’re thinking about retrofitting one or more dormer windows in an existing house, the best time to do it is when you’re replacing the shingles. That way, the roofing contractor can lay new shingles over the entire roof at the same time. This provides the most cohesive look because it can be difficult to perfectly match new shingles to existing ones.

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