Proportion and Scale
A dormer should be a detail on a roof, not its dominant feature. To help ensure the right sense of proportion, dormer windows are usually smaller than windows on the walls below. Another good rule: Don't let dormers occupy more than half the width or depth of the roof.
The front face of this house has a trim, well-planned look, largely because of the care taken to line up windows in the dormers and on the walls below. In addition, all of the windows have a similar design with small panes of glass stacked on top of each other.
Just as artists use the concept of a vanishing point to convey a sense of distance, you can design dormers to look bigger or smaller than they are. This dormer minimizes its apparent size. The porch-style hip roof in front keeps the gable roof in back much smaller than it would have been if the gable extended to the front. Adding to the illusion of small size, the top window has smaller panes so it looks farther away.
When extra space is needed upstairs, the easiest solution is often to add a wide shed dormer. From the exterior, however, these dormers can sometimes look overwhelming. Grouping the windows adds a welcome bit of variety to the design, and it has a practical benefit: If you want to divide the space behind the windows into two rooms, there's a place for a wall.
Shed Plus Gables
Instead of extending a shed-type dormer across most of a roof, you can also take the approach shown here: Locate gable dormers on the ends, and connect them with a recessed shed dormer. Besides resulting in an interesting look that isn't too massive, this design allows you to create cubbyhole-type spaces inside the gable ends. A writing desk or a window seat would fit nicely.
This house features two shed dormers, one on top of the other. Shed dormers are easy to build from scratch, but clever builders can speed the process when a dormer is being added to an existing house. Leaving the existing roofing intact, they cut rafters where the dormer will be. Then they tilt and lift that section of roof and prop it up. Presto! Once they build walls underneath, the dormer is basically done.
Fit into a steeply pitched mansard roof, this shed dormer sits almost flush with the surrounding slates. Mansard roofs are similar to hip roofs except that each side has two parts: a steep section near the walls and a barely slanted section toward the middle of the building. This creates an attic that's fully usable, so it's probably no surprise that dormers often are found on mansard roofs.
Not your basic gabled dormer, this one features an intricate truss design, which is characteristic of houses with half-timbered details. Today, this look may be purely decorative, created simply with nailed-on boards and plaster. Originally, however, the wooden pieces were part of the house's basic structural skeleton. They helped brace the main beams so they didn't twist out of shape.
A boldly painted crest and simple gable decoration add to the look of this large dormer. Dentil molding, named for the way it resembles a row of teeth, emphasizes the triangular shape of the pediment. Instead of the full columns found on some pedimented dormers, this one has only shingle-covered side walls that bulge out on top.