Issue link: http://alpine.uberflip.com/i/493471
1 2 3 4 5 6 7 8 3.19 ROOF TRUSS SYSTEMS - PIGGYBACKS Cap truss installed on top of base truss. Note continuous bracing on top chord of base truss and connection clip. Applications There are instances when a roof truss application, due to a combination of roof pitch and truss span, will require trusses that would be too tall to build, deliver or handle economically. In such instances, two or more trusses can be built and delivered which will, when installed together, do the work of each single, oversized truss. Of these two trusses, the bottom component is called the base truss and the truss that rides on top is called the piggyback or cap truss (see illustration). As a rule of thumb, individual trusses that would be over ten to twelve feet tall would probably be candidates for a piggyback system. Installation Sequence During installation, piggyback system base trusses are installed first and proper bracing is installed for the base truss set. Base trusses must be installed to resist the uplift forces of the entire piggyback system. Bracing of the top chords of the base trusses is essential and is often accomplished using roof decking/ sheathing or continuous purlins. This bracing must be completed prior to the installation of the cap trusses. Cap trusses are then attached to the base trusses in a proper manner to resist lateral and uplift forces. Connections of the cap trusses to the base truss set are sometimes made using proprietary connectors (see Section 5). Decks or purlins for the roof membrane system may then be applied to the cap trusses. During design and estimation, designers and contractors will want to account for these additional materials as well as for the fasteners required to install decking, purlins, clips, etc. Additional labor may be required to install these materials and the piggyback trusses. Piggyback System ENGINEERED BY ALPINE T R U S S D E S I G N M A N UA L ENGINEERED BY ALPINE S P E C I F Y I N G / D E S I G N I N G