A house truss or roof truss is a framework made of wood or metal, designed to support the structure of the roof. Trusses are engineered to handle the weight of the roof, withstand the energy force of wind on the structure, and provide stability to the overall structure. Trusses are typically manufactured to the builder’s specifications and delivered to the construction site. Trusses should be put in place using a crane to minimize physical handling, and possible damage to the trusses during installation.
Residential roof trusses are constructed in different shapes and sizes, depending on the design of the home, and are usually made of wood. Trusses are configured as a series of triangles, because a triangular shape distributes load forces evenly across the truss. The bottom of the truss (bottom chord) spans across the house structure, and beyond the walls on both sides. The bottom chords form the rafters, which are the framework for the interior ceiling. The parts of the bottom chord that extend beyond the walls, form the framework of the eaves. The top boards of the truss (top chords) form the framing for the roof.
Preparation before setting the trusses includes: marking the upper plates (top of the walls) at 2-foot intervals, cutting pieces of wood that will be used as blocking between trusses, and building a temporary bracing structure to hold the first truss in place until it can be secured to other trusses.
Set the first truss in position and brace it, making sure it is positioned vertically and placed on the walls correctly. Secure the first truss to the bracing, and position pre-cut blocks on top of the walls against the truss. The pre-cut blocks maintain the positioning of subsequent trusses at 2-foot intervals. Continue adding trusses and blocks.
Install lateral bracing between trusses by fastening a long 2 x 4 piece of lumber to the bottom edges of the truss top chords or vertical truss members. The lateral bracing will parallel the walls. Measure to ensure that 2-foot spacing is maintained between trusses before attaching the truss to the lateral bracing.
Install diagonal bracing when all of the trusses are in place. Diagonal bracing is a long 2 x 4 piece of lumber that is installed on the interior of the trusses at an angle to the walls. No measurements are required when installing diagonal bracing.
Setting trusses is the most dangerous activity associated with home construction. It requires workers to walk along the top plates of the walls without netting or safety harnesses. Work slowly and cautiously.
- Photo Credit roof turss image by Greg Pickens from Fotolia.com
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