The loads on the truss are generally in a downward direction, but may turn upward during extreme wind.

Which chord carries tension and which carries compression depends on the direction of the overall loading on the truss. In a truss, the bottom chord and the top chord are under tension and compression forces as a result of the loads on the roof.

T-bracing takes more time to install than continuous lateral bracing and is more expensive, but it’s more effective and easier to install correctly. Nail plates: Components are fastened together with toothed metal plates that are machine-pressed to the members.īetter bracing: Nailing 2×4 T-bracing to the top edge of long web members prevents them from deflecting sideways. Individually, the web members may be in either tension or compression, depending on their location in the truss and the direction of the loads on the truss. Web: Helps to support and transfer the compression and tension forces from one chord to the other. The bottom chord also serves as a rafter tie and keeps the top of the exterior walls from bowing outward. Top chord: Supports the dead load of the materials used to construct the roof, plus the live loads exerted on the building.īottom chord: Supports the dead load of ceiling materials and the live loads of people or objects. Live loads are those added by wind, snow or workers building or maintaining the structure. To get you started, here are a few important terms:ĭead loads: The weight of the roof, the truss itself, attic insulation, floor sheathing, ductwork, and drywall used for the ceiling. While almost all trusses are made in a factory and trucked in, site-built trusses also are a possibility. Trusses are typically set into place one at a time, either by hand or with the help of a crane, but in some cases some trusses can be assembled on the ground and lifted into place as a single sub-assembly. There are many kinds of roof trusses, making it possible to use them even on complex roof designs. Whether you’re framing a new roof or remodeling an existing truss roof, it’s important to know what components make up a truss and how the assembly works. The most common truss, a 2×4 Fink truss, is designed to support several different loads. Cutting a truss can have consequences ranging from damage to interior finishes to catastrophic roof failure.Ī roof truss is an engineered building component designed to span longer distances than dimensional lumber without relying on interior partition walls for support. Munach stresses that trusses cannot be modified in the field. An illustration shows the compression and tension ratings of a truss that has been modeled with a combined dead, live, and snow load of 40 lb. In this “How It Works” column, structural engineer Rob Munach explains how trusses carry their loads and how T-bracing and roof sheathing add strength. Synopsis: The roofs on most new houses in the United States are built with trusses.