Lessons Learned from Recent Failures of Structural Timber Appurtenant Assemblies

Two recent structural failures in California resulted in fatalities, casualties, and subsequent changes in state building code regulations. Both failures were associated with wood framed construction and structural timber appurtenant assemblies, which are now identified as timber-framed exterior elevated elements, or EEEs. The California Building Standards Commission developed emergency changes to California Building Code regulations to address EEE issues identified as contributing to both failures. The “as-built” construction of the Berkeley balcony utilized three (3) layers of wood structural panel (WSP) horizontal sheathing nailed to the top of the cantilevered timber joists. Despite an exhaustive literature search, the authors were unsuccessful in finding research relevant for psychrometric evaluation of the multi-ply “as-built” construction of the Berkeley balcony. This paper presents the findings from the authors’ testing program developed and conducted to specifically evaluate wetting and subsequent drying rates of multi-ply assemblies of near-horizontal WSP.

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