Roof Types and Components
Types of Roofs
Following are the most common types of roofs used in residential construction. Click on each term to find out more:
A gable roof has two slopes that meet at the center (ridge) to form a gable at each end of the building. It is simple, economical, and can be used on any type of structure.
A hip roof has four sides or slopes running toward the center of the building. Rafters at the corner extend diagonally to meet at the ridge. Additional rafters are framed into these rafters.
A mansard roof has four sloping sides, each of which has a double slope. As compared with a gable roof, this design provides more available space in the upper level of the building. The upper slope is typically not visible from the ground.
Gable and Valley Roof
A gable and valley roof consists of two intersecting gable roofs. The part where the two roofs meet is called a valley.
Hip and Valley Roof
A hip and valley roof consists of two intersecting hip roofs.
A gambrel roof is a variation of a gable roof. Here, each side has a break, usually near the ridge. The gambrel roof provides more available space in the upper level.
A shed roof is a flat, sloped construction. It is common on high-ceiling contemporary construction, and is often used on additions.
Roof Framing Systems
There are two basic roof framing systems.
In stick-built framing, ceiling joists and rafters are laid out and cut by carpenters on a site and the frame is constructed one stick at a time.
In truss-built construction, the roof framework is prefabricated off site. The truss contains both the rafters and ceiling joist.
Basic Roof Layout
Rafters and ceiling joists provide the framework for all roofs.
Components of a Roof
The highest horizontal roof member, a ridge (ridge board) helps to align the rafters and tie them together at the upper end. The ridge board is one size larger than rafters.
2) Common Rafters
A structural member that extends from the top plate to the ridge in a direction perpendicular to the wall plate and the ridge. Rafters often extend beyond the roof plate to form overhangs (eaves) that protect the side of the building.
3) Hip Rafter
A roof member that extends diagonally from the outside corner of the plate to the ridge.
4) Valley Rafter
A roof member that extends from the inside corner of the top plate to the ridge, along the lines where two roofs intersect.
5) Jack Rafter
A roof member that does not extend the entire distance from the ridge to the top plate of a wall. A rafter fitted between a hip rafter and valley rafter is called a cripple jack. It touches neither the ridge nor the plate.
A plate is the wall framing member that rests on top of the wall studs. It is sometimes called a rafter plate because the rafters rest on it. It is also referred to as the top plate.
On any pitched roof, rafters rise at an angle to the ridge board. Therefore, the length of the rafter is greater than the horizontal distance from the plate to the ridge. In order to calculate the correct rafter length, the carpenter must factor in the slope of the roof.