Adding a dormer creates valuable ceiling space in the home while adding visual appeal to your roof line. But this extra bit of headroom comes with a high price tag, and dormer installation is not a DIY project. Plan to spend between $10,000 and $30,000 for your new dormer, depending on size and style.
Dormers come in decorative an functional varieties. Decorative units are relatively small and inexpensive, and attach to the top of the room without adding extra ceiling height to the interior of the home. Functional dormers are larger and more expensive. They require an opening in the roof, along with new framing and structural support. Installers add flashing to prevent roof leaks, then add shingles over and around the new dormer.
A shed dormer is the cheapest dormer style and features a rectangular shape with a roof that slopes down away from the home. A standard gable dormer is a mid-range option and features a steeply sloped roof on either side, similar to the profile of a gable roof. A hip dormer is slightly more expensive and features a roof that slopes toward both the front and either side. If you want a more complex dormer design, boost your budget; arched, eyebrow or barrel profile dormers are more difficult to frame and cost more than more traditional dormer styles.
Cost and Style
Decorative dormers range from $583 to $933, according to a 2013 report by Dryden Mutual Insurance. An average 10-by-15 shed dormer costs between $11,270 and $16,904, while the same size gable dormer ranges from $14,400 to $21,602.
Dormers and Attic Remodels
Homeowners typically add dormers as part of the process of transforming the attic into a usable living space. Adding a 15-foot shed dormer to accommodate a new 15-by-15-foot bedroom and 5-by-7 bathroom in the attic costs an average of $49,438 as of 2014, according to Remodeling Magazine. This price includes adding the dormer as well as framing and finishing both rooms, plus all applicable plumbing, electrical and fixtures.
If adding a dormer is beyond your budget, consider a skylight. Materials cost just a few hundred dollars if you want to tackle this project yourself, while professional installation rings in at around $2,000, according to a 2012 article by Popular Mechanics.