Install an Attic Dormer Window

An attic bedroom must include a window that can serve as an emergency exit if necessary. The window opening must be large enough for a person to fit through. Image: Valspar Paint

If you’re remodeling your attic into living space, you’ll need to add a dormer window. An attic dormer window opens up your roof to accommodate air, light, and in case of emergency, an exit. A dormer structure includes its own roof and siding, and from the outside is a prominent architectural feature. On the inside, an attic dormer provides additional headroom and valuable floor space.

Choosing a dormer style

Seen from the outside, a dormer window should have proportions and style that fit your house. The most common types include shed, gabled, and hipped. Inset and eyebrow dormers have flair but are more costly to construct.

Before consulting an architect or general contractor, it’s a good idea to make drawings of what you’d like. Creating rough sketches is an excellent way to engage in efficient discussions with an architect or general contractor.

Begin by taking digital photographs of your house and printing multiple copies. Then, sketch in ideas for your dormer, trying out various styles and sizes. Keep in mind that these are preliminary ideas. Structural limitations and other issues may alter the size and location of your dormer.

Your architect or general contractor will help with important construction details, such as locating load-bearing walls. They’ll also know if local codes or covenants apply to the dormer and if you need to apply for a permit.

Architects charge $50 to $150 an hour for a consultation, and 5% to 20% of the final cost of the project if you hire them to complete drawings for an entire attic remodeling job. A general contractor charges a similar fee if their services include creating drawings needed to obtain a building permit from your local building department.

Dormer construction

To build a dormer, the contractor cuts a hole in your roof, adds framing, and installs windows. Then the roof and sides of the structure are sealed against weather and finished so that the new structure blends with your existing exterior roofing and siding.

Sealing the dormer involves installing galvanized metal flashing where the new roof and siding intersect the existing roofing. A qualified roofing contractor should complete this portion of the work. Be sure to inspect this new flashing annually to keep it free of debris and to check for any signs of pitting or rust.

Because your roof will be open during construction and the interior of your house exposed to the elements for a period of up to a week, you’ll want to coordinate with your contractor to try and schedule the job when rain isn’t in the forecast. Nevertheless, have your contractor agree to provide temporary protection against the weather at the close of each work day.

Costs of dormer construction

Final cost depends on the size of the dormer, the quality of windows and finish materials, and the steepness of the roof (which affects the difficulty of the job). Expect to pay $5,000 to $20,000, including the cost to insulate, provide electrical outlets, and finish the interior of the dormer, according to costhelper.com.

Shed dormers give the biggest bang for your buck because the simplicity of their construction reduces labor costs and the amount of materials required. The cost of framing a shed dormer is approximately 40% less than the cost of a gable roof dormer using similar materials.

Choosing windows and emergency egress

A good rule of thumb is that the windows in the dormer be at least 75% of the area of the wall in which they reside. To ensure architectural harmony, select windows that blend with your existing windows and the overall style of your home.

Because these windows provide emergency egress from your attic bedroom, the operable side of the window—the part that actually opens—must be large enough to permit someone to escape through. Universal building codes specify that the window must have an opening equivalent to a minimum of 5.7 square feet and be no less than 20 inches wide or 24 inches high. Your local code may differ—be sure to check.

Note that a 20-inch-wide window should be at least 41 inches tall to comply with the minimum 5.7 square-foot requirement for an egress window. Similarly, a 24-inch-tall window must provide a clear opening at least 34.2 inches wide.

Your egress window should include an escape ladder. Fold-up and chain-type ladders for a third-story window can run $70 to $100. Expect to pay up to $300 for types that come with their own wall cabinetry to keep them tucked away but accessible. Be sure to tell anyone staying in the room where the ladder is and how to use it.

Energy-efficient dormer windows

Look for energy-efficient windows that help reduce the energy needed to heat and cool your attic room. The type of window you choose may depend on where you live in the country and which direction the dormer window faces.

If your house is in the northern tier of states, it’s important for windows to have high insulating capacity so heat doesn’t readily escape from inside the room. If you live in the South, consider windows with special coatings that block sunlight and reduce solar heat gain.

For help deciding which type of window is right for you, refer to the Energy Star information provided by the U.S. Department of Energy. Expect to pay $150 to $350 for an insulating vinyl, vinyl-clad wood, or all-wood frame window.

Adding storage and window seat

Storage in remodeled attics can be difficult to provide because of the angles of the sloped ceiling. Look for extra room behind the knee walls—short walls that intersect the sloped framing members of the roof—and making built-in cabinetry behind them. Any cabinets and shelving should be completely enclosed at the top, sides, back, and bottom, and insulated with rigid foam.

A good opportunity for storage is to build a window seat within the dormer. A lift-off lid for the seat provides access to a storage compartment. A built-in window seat provides an ideal place to tuck an escape ladder out of sight, but right next to the window.

Benjamin Allen has been the editor of dozens of home improvement, remodeling, and home repair books published under the Better Homes and Gardens, Home Depot, Stanley, and Ortho brands. He currently is a freelance writer and editor and makes his home in Des Moines, where his Craftsman-style house built in 1912 keeps him busy with both repairs and upgrades.