Now is the time to consider Spruce-Pine-Fir (SPF) as a substitute for Southern Pine (SP). As noted below, #2 SPF’s 19% higher bending value and only 10% lower compression value usually enables longer spans. Cull rates are generally lower with SPF, and it is lighter and easier to handle.
Since the relative prices of SPF and SP often diverge, consider using hybrid lumber as shown in the box on the drawing. On this 40-foot truss, the lower of the structural values of SPF and SP are used in design calculations, so that either grade of #2 lumber may be used. On the truss chords (see chart), only Fc, the compression value, is lower for #2 SPF. However the considerably higher bending value more than compensates. On the web members, only Ft, the tension value, is lower for SPF Stud (by only 4%). However, Fc, the compression value, is 36% higher. One caveat applies – the truss plate design values for SPF are lower than SYP which may raise plate cost – but consider also whether smaller plates would be prudent on a 40-foot truss.