Roof Framing 101

Gables

• Gable roofs, perhaps the most common type of roof in residential construction, form a triangular section on two sides. Rafters usually extend beyond the house on the ends without gables walls to form an overhang. You also need to build an overhang on the gable sides, about the same length as the one on the nongable ends, to give the house a more attractive appearance. Instead of using individual rafters, an alternative way to frame a gable roof is to use trusses, framing members that have a triangle shape, although this method leaves you with less attic space.

Sheds

• Shed roofs, unlike gable roofs, have only one sloped side. The ends of a shed roof rest on top plates, the large beams that run along the top of the exterior walls. Both ends of the rafters for shed roofs need a notch so they will fit securely onto the plates. The cut, called a bird's-mouth, should never exceed one-third of the rafter's width. Rafters should always fit on the top plate directly over a wall stud.

Hipped

• Another type of roof style, the hipped roof, has several variations. Hipped roofs have four slopes, with the ends of each slope resting on an exterior wall. Some hipped roofs require a ridge pole, a long beam at the top of the rafter bay. The pyramidal hipped roof, however, is framed without a ridge pole and has the four slopes intersecting at the top of roof. Another way to frame a hipped roof, called a mansard roof, uses eight slopes -- four at the top of the roof and four at the bottom, with the lower section having the steeper pitch.

Gambrel

• Gambrel roofs, often seen on barns, consist of two gable roof sections that have different slopes. Like the mansard roof, the lower portion has a steeper pitch. Framing gambrel roofs requires cutting two sets of rafters, typically a shorter set for the upper section and a longer set for the lower part. Some type of support, such as a post or a framed wall, is required where the two sets of rafters insect.