To use this chart, locate your required clear span in the Lmax columns. In adopting this rule, we encourage builders and designers to ignore the reduced live load of 30 psf for sleeping areas, and instead use the standard 40 psf live load for all rooms. After all, a bedroom can become a study or home office, and the traffic may be heavier than in a living room. The consensus among wood truss professionals is that strongbacks are effective in minimizing annoying vibrations, and that they are well worth the time and money it takes to install them. Table 2 illustrates the expected performance of various floor truss designs, using a 40-psf live load.
Ratings apply to maximum spans at the tabulated deflection limit.
The ratings are based on specific input from experienced wood-truss design professionals, and our interpretation of opinions of experts and case studies. Table 3 gives guidelines for sizing and installing strongbacks. The strongback should also be located at the bottom of a vertical web. To be effective, the strongback must be snugly attached to each web, as indicated by the nailing recommendations in Table 3. The total number of nails used to attach the scabs to the truss chords should match the number used to attach the strongback to the vertical web.