Sound Attenuation in Cold Formed Steel Trusses:
BuildSteel.org has posted an article with tips on lessening sound transmission in CFS floor systems (link below). While the Buildsteel article speaks specifically to joists, the strategies mentioned are applicable to CFS Trusses. Depth plays a critical role in the design of cold formed steel trusses. In general - the deeper the truss the lighter the members. It turns out depth plays a big role in sound reduction as well, the deeper the joist or truss member the less sound will transfer between floors. Since trusses can be fabricated deeper than standard joists a truss may be a better option for a quieter floor system. Spacing of supporting members will also have an effect because sound may be lessened by ‘decoupling’ in a floor. A wider cavity, or space between joists/trusses, results in a greater ‘buffer’ or separation between sound transferring members. This is even more advantageous if insulation fills the cavity between joists/trusses. Again, this makes using CFS Trusses beneficial compared to joists; since trusses typically have greater load carrying capacity they may be spaced further apart than the more shallow CFS joist, increasing the decoupling in a floor system. Incidentally, this also results in fewer pieces to install and easier access for mechanicals. And finally, for improved sound attenuation it is best to screw the subfloor to the truss/joist support away from the joist/truss web, in other words, as far out on the flange as possible. This gives the Advant Steel Truss Chord a distinct advantage over other CFS Truss systems. The wide flange of the Advant truss chord allows the subfloor to be attached further from the web, even when subfloor seams butt over the same truss.