In 1994, a seismic event in Northridge, California caused between $16 billion and $20 billion worth of damage to multi-family wood apartment buildings and brought to question construction quality, framing practices, structural design methodology, and the role of local jurisdiction in adoption, enforcement and oversight of building codes. The majority of damage to wood-framed structures occurred in apartment buildings of 3 stories or less; damaged structures showed evidence of inadequate or complete lack of structural designs and poor construction quality associated to building age and structural irregularities. Specifically, 'tuck-under parking' apartment building presented some of the most significant failures due to the weak-story condition created by the lack of rigidity in the lower level space frames as well as building code allowances for the use of prescriptive path methods without the approval of a licensed Architect or Engineer, a construction method still available in most jurisdictions, but now subject to significant limitations. The 1997 edition of the Uniform Building Code (UBC) incorporated revised seismic hazard maps and regulated prescriptive path construction methods for wood commercial buildings resulting in trends towards the use of concrete or steel for mid-rise apartment buildings. Specifically, designs which incorporated known significant structural irregularities or reached the maximum allowable height limit of the code, a minimal level of partial design by a licensed professional became mandated by the code.
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