The Main Components of a Roof
Before you can have a discussion about what parts make up a roof, you will need to know a few terms. These terms identify the various architectural aspects of a typical pitched residential roof. Becoming familiar with these terms will enable you to understand a discussion of how roofs are constructed.
The first term is the roof plane. If you recall from geometry class, a plan is a flat surface. In roofing terms, the roof plane is the pitched face of the roof.
To describe the places where roof planes meet we use the terms ridge, hip, and valley. The ridge of the roof is the highest point on the roof where two pitched planes meet. A hip is a place where to planes meet and project outward. A hip is similar to a peak, but is not at the top of your roof and is usually not horizontal. A valley, just like it’s geographic namesake, is a place where to planes meet and project inward.
A dormer is a common feature on many two-story houses. It is a projection from the main plane of the roof that usually houses a window. The dormer is usually constructed to add space or natural light to the room inside.
The gable is not exactly part of the roof, but still an important term to recognize. It is the triangular part of the exterior wall that spans the area between the pitched roof planes.
Structural Layers of the Roof
Just like the rest of the house, the roof starts out as a frame. The frame is usually constructed of lumber. It incorporates joists, trusses, and rafters. Together, these three types of beams make up a framework that gives the roof its shape. The frame needs to be strong enough to support the weight of the roof. With a standard asphalt shingle roof, this is not much of a concern. But if you plan to use heavier materials like tile or slate, you may need to add extra supports at this stage.
Once the frame is in place, it is covered in decking. Decking is the skin that covers the frame and creates the base that the rest of the roof will be built upon. The most common material for decking was once plywood. However, in recent decades oriented strand board (OSB) has taken over as the most common material for load-bearing planks in residential construction. OSB is similar to particle board, but instead of tiny bits of wood, it is made up of thin strips of wood. The strips are held together with resin and a small amount of wax to form a very strong plank.