Lateral restraint for top chords
Downward loads on the roof cause compression in the top chords. Long slender members tend to buckle sideways in compression. Top chords are long slender members and, therefore, they tend to buckle sideways.
Trusses need to be prevented from buckling because this causes them to move outside their plane of strength (ie plane of vertical strength). Fixing roof battens to the top chords at regular intervals restrains the sideways movement in the top chords. Battens should be fixed to every truss, including each ply of double and triple ply trusses.
