Truss Uplift
Question:
What is truss uplift?
Answer:
Truss uplift can describe two completely unrelated conditions. The first condition called truss uplift, also called truss arching, is one of the causes of partition separation. SBCA’s TTB – Partition Separation Prevention and Solutions describes this issue and ways to prevent it. Truss arching occurs because of a moisture content difference between the top chord and bottom chord of the truss. One easy way to avoid this scenario is to ensure plenty of ventilation of the attic space, avoid discharging household vents into the attic and ensure that ventilation areas are not blocked by insulation.
The second condition referred to as truss uplift is the tendency of framing (trusses, rafters, joists, etc.) to lift off their supports due to wind forcing them upward, or due to multiple bearings or cantilevers. These uplift forces are generally listed on truss design drawings. In some cases, toe nailing the framing to the top plate does not provide enough resistance to the uplift force and a mechanical connector like a metal hurricane tie, anchor or clip must be used. For a more thorough description of this option, see SBCA’s BCSI-B8 Summary Sheet.