Roof Collapse: Forensic Uplift Failure Analysis

Many factors affect the performance of structural roof framing, and if deficient components exist, the structural integrity is compromised. When a roof system is improperly designed, failure may result from under-design regarding net uplift pressures. Today's commonly used lightweight roofing products (EPDM, poly-isocyanurate) have made net uplift loads a more critical design load, and in some instances, the controlling case. In particular, a commercial warehouse building was under-designed for net uplift pressures, which in conjunction with unclear bridging spacing requirements per Steel Joist Institute (SJI) requirements, resulted in a roof collapse during a storm event. The net uplift design load for the steel joist roofing system should have been higher than what was specified on construction drawings. Additionally, a lack of clarity in the SJI requirement for joist bottom chord bridging resulted in excessive bridging spacing, which lessened the capacity of the roof framing considering uplift. Consideration of the lightweight roofing materials in the joist design and clarity in SJI uplift tables would have prevented the roof collapse.