Although the usual spacing of roof trusses is similar to that of rafters, with 24-inch spacing being a frequent choice, the design of a truss may allow for the use of a cheaper grade of lumber than would be necessary for rafters with identical spacing and span. For example, some truss designs can be built with 16- or 18-gauge steel rods as main supports instead of 2x4s or 2x6s, which would be required if conventional timber framing techniques were used. The typical truss has three top chords that are connected by two bottom chords. The top chords connect the ends of the gable walls while the bottom chords connect together the ends of the house walls. The trusses are then braced with crossbars to keep them from sagging under their own weight. Roof trusses should be able to support the entire load on the roof without bending. In other words, they should have enough depth in the middle to prevent kinking. Types of Trusses: Gable-top trusses have two parallel top chords that extend the length of the roof along the ridge line. The top chords are usually made of metal because they need to withstand the force of gravity on their own. They may also be made of wood if you want the truss to look decorative. Bottom-hinged trusses have one central bottom chord that extends the full height of the roof.