Roofs are structurally supported primarily by their underlying framing system, which bears the weight of the roofing materials, snow, wind, and other loads, transferring them down through the walls and foundation.
This support is usually provided by two roof framing systems—rafters and trusses. Each has unique characteristics, but both play a crucial role in supporting the entire roof structure. These systems create the necessary shape and pitch for the roof while ensuring its stability and integrity.
Rafter Framing
Rafters are sloped beams that extend from the eaves (the edges of the roof) up to the ridge (the peak). They are typically installed individually, one by one, on-site.
- Key Characteristics:
- Traditional framing method.
- Allow for greater flexibility in roof design, such as incorporating dormer windows or varying pitches.
- Often require load-bearing walls or beams within the structure below to support the rafter span.
- Can sometimes create more usable space underneath, like an attic, as the rafter structure leaves the area largely open.
Truss Framing
Trusses are prefabricated structural components, often triangular in shape, built in a factory and delivered to the construction site ready for installation. They consist of multiple members connected together to form a rigid framework.
- Key Characteristics:
- Highly efficient at distributing loads.
- Can span long distances without requiring intermediate supports like load-bearing walls.
- Cost-effective and faster to install compared to traditional rafter systems in many cases.
- The internal web of members within the truss often occupies the attic space, making it less usable for storage or living areas.
The Crucial Role of Roof Framing
Whether using rafters or trusses, the framing system is fundamental to the structural performance of a building. It not only supports the roof covering but also helps brace the walls and resist lateral forces from wind and seismic activity. The choice between rafters and trusses often depends on factors like budget, desired roof design, building span, and construction timeline.
