Dormer fundamentals

An attic dormer window opens a slice of roof to accommodate air, light, and in case of emergency, an exit and entrance. From the outside, a dormer is a prominent architectural feature with its own roof and siding. On the inside, an attic dormer provides additional headroom, versatile floor space, and extra storage.

Dormer window drawings

A dormer window should look like the house it tops. The most common types include shed, gabled, and hipped. Inset and eyebrow dormers have flair but are more costly to construct. 

Guide your architect or general contractor by sketching a few drawings. Your architect will have more ideas—that’s what you pay for—but your sketch is an efficient way to start the discussion.

If drawing isn’t your forte, take digital photographs of your house, print several copies, then Sharpie in your dormer ideas. But don’t fall in love with your work: Structural limitations and practicalities may alter the size and location of your dormer.

Role of professionals

Your architect or general contractor will locate load-bearing walls and research local codes, permits, and/or covenants that may apply to your remodel.

Architect fees vary greatly, but they typically charge $50 to $150 an hour for a consultation, and 5% to 20% of the project cost. A general contractor charges a similar fee if services include creating drawings and pulling permits from your local building department (something you can do yourself to save money).

Steps for building a dormer

  • Construction: Contractor cuts a hole in your roof, adds framing, and installs windows.
  • Sealing: Installs galvanized metal flashing where the new roof and sides intersect the existing roof. 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, pitting, or rust.
  • Finishing: Finishes dormer sides and roof to blend with existing exterior roofing and siding.

Elemental protection

Installing an attic dormer window means your roof will be open and the interior of your house exposed to the elements for at least a week. Your contractor should provide temporary protection against the weather at the close of each workday.

Dormer costs

Final cost depends on the size of the dormer, quality of windows and finish materials, and the steepness of the roof (which affects the difficulty of the job). Expect to pay $2,500 to $20,000 for exterior work. Interior finishing is extra.

Simple shed dormers are most economical, costing 40% less than a gable roof dormer using similar materials.

Window specifications

To ensure architectural harmony, select windows that blend with existing windows and the overall style of your home. Aesthetically, a dormer window should be at least 75% of the area of the wall in which it resides.

Dormer windows that provide emergency egress should comply with the following code specifications.

  • The operable side of the window—the part that actually opens—must be large enough to permit someone to escape through.
  • The window must have an opening equivalent of at least 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. Also, it’s a good idea to place an escape ladder next to your egress window. 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.

Select energy-efficient windows

Energy-efficient dormer windows help reduce the cost of heating and cooling your attic room. Climate and dormer position will influence your window choice.

If your house lives up north, choose windows with high insulating capacity; if it lives down south, pick windows with coatings that block sunlight and reduce solar heat gain. Expect to pay $150 to $350 for an insulating vinyl, vinyl-clad wood, or all-wood frame window.

Energy Star information provided by the U.S. Department of Energy can help you decide which window  is right for you.