Roof Truss Bottom Chord

Roof truss uplift occurs when the bottom chord of the truss is exposed to significantly different moisture or temperature conditions than the rest of the roof truss.

Roof truss bottom chord.

The roof system is basically a hinge now. The horizontal beam of the triangle of a bottom chord is used in this simple triangle truss construction. In standard heel applications of roof trusses the bottom chord is cut on each end at an angle consistent with the roof pitch of the truss. This creates additional surface area for the two members to transfer forces and allows for them to be plated together creating a strong resilient joint.

Removal has left them extremely vulnerable to collapse due to spreading especially under snow loads but also under just the load of the roof itself. The stability of this shape supported by the bottom chord is the reason for the common usage of the triangle truss. It is utilized in a framed roof comprised of rafters and a ceiling joist. Those trusses were engineered with a heavy critical dependency on the bottom chords which are in tension.

The trusses are 42 long with a 2x10 bottom chord 3 12 pitch. And the responses from the experts and my take on each one.