Top Chord

The top chord is one of the three key components to any truss. In addition to the bottom chord and webs, the top chord is used to create the upper perimeter of the structure, or the roof. The top chord is configured to resist live loads such as those applied during construction, as well as wind loads, snow loads and others. It also resists more permanent dead loads like sheathing and roofing materials. For traditionally spaced trusses, the top chord is cut out of 2x4 or 2x6 dimensional lumber but can also be cut out of 2x8, 2x10, or 2x12 material for roof trusses. Factors that determine the size of the top chord include on-center spacing, dead and live loads applied to the truss, span, and pitch applied to the top chord.

The top chord is intersected by the bottom chord and web members at various points through the truss creating a joint that is secured by metal connector plates. A top chord can be multiple pieces of lumber secured by a metal plate known as a splice, either at a joint or mid panel. While a vast majority of trusses will have top chords of the same species and grade, changes in both lumber species and grade are possible at splice points.

In typical trusses with an overhang, the top chord is extended past the bearing over the bottom chord to create an eave condition for the structure. Most top chords are cut with a plumb cut at the peak and overhang and a square cut at splices.

For floor trusses, the top chord material is usually cut from 2x3 or 2x4 material, but instances utilizing 2x6 top chord material for floor trusses can also be found. Typically in floor trusses, the material is oriented in a flat or 4x2 position. Orienting the chord material in a 4x2 manner creates a very stable truss that allows installers the ability to easily walk across members without tipping the truss during installation of additional members or floor deck sheathing.

0
0