Load bearing

Most roof trusses are only designed to be supported on external load bearing walls.

Diagram showing truss on wall supports. One wall is a partition built with no gap to the bottom chord of the truss. The truss deflects down due to dead and/or wind load. Stresses not designed for are placed on nail-plates. The web, designed for tension forces only, now has compression forces. The bottom chord, designed for tension forces, now has bending forces.