How to Add a Dormer Window to an Attic

Draw All Framing

• You will need a detailed plan of your home’s existing framework. A drawing of attic rafters and floor joists, along with wall framing, will help you figure out the best dimensions of an attic window. Each dormer window requires framework to define the box shape of the exterior dormer. A dormer that is either too small or two large will affect the balanced look of the house.

Design New Framework

• Dormer windows affect the interior of the attic as well. You will need to construct interior framework of 2-by-4-inch boards that encloses attic space around the dormer window. You can also construct a dormer window system whereby the roof is lifted. Envision this type of dormer area as a rectangle cut out of the roof area and lifted up to form a wedge shape. The building process involves adding a set of windows along the front of that wedge.

Opening the Roof

• Inclement weather is a big factor during construction. When you open the roof to build the window framework, build it over a couple of days in sunny weather. Existing house framework will need reinforcement on the interior to keep rafters intact. Enlist the help of an expert carpenter to cut the opening and build the new framework. An expert can remove specific sections of the roof covering, so you can cut and replace the asphalt shingles in manageable steps around the new dormer.

Use Flashing

• The installation of metal flashing for weatherproofing is critical around dormer windows. The various angles and valleys created on the roof by the attic dormer box shape all require flashing. Otherwise, the roof will leak. Over time, the leaks may affect the living space on the floor below. Flashing needs a sealant, such as tar, to keep out moisture properly. Shingles for the roof area of the dormers are applied after flashing is in place.

Add Well-made Windows

• Energy-efficient windows are important for the dormers. Whether or not you build a room in the attic, you want to prevent air leakage around windows. The windows need to keep out rain and snow as well. Purchase high-quality windows with a long-term warranty of 20 years or more.