Since at least the 1971 San Fernando, California Earthquake (M=6.6), engineering investigation has understood that multi-unit, wood frame, residential buildings with weak first stories that lack adequate lateral strength or stiffness (usually because of ground level parking space openings or commercial space store front openings) can pose significant risk of catastrophic leaning and collapse during strong earthquake ground shaking. In California, this knowledge has been reinforced by the 1989 Loma Prieta earthquake (M= 7.09) and the 1994 Northridge earthquake. (M=6.69)

Soft-story, multi-residential building, Los Angeles, 1971

Collapsed soft-story buildings, San Francisco, 1989

Collapsed soft-story building, Northridge, 1994 (from SEAONC)

In 2008, the Association of Bay Area Governments (ABAG) identified 24,273 at-risk units in 1,479 residential buildings with 5 or more units, 2 to 7 stories, built before 1991, and containing parking or commercial uses on the ground floor in the City of Oakland, California. A related ABAG statistical sample inferred the existence of more than 1,400 additional ‘potential soft story buildings’ with less than 5 residential units in Oakland. An NBC report in Los Angeles observed that according to Caltech engineers, there are “more than 20,000 soft-structure apartment buildings in the City of Los Angeles alone and only 800 of those have been seismically retrofitted, according to the LA Department of Building and Safety.”

Engineering research into the complexities and remediation methods for multi-unit, wood frame residential buildings with soft stories is extensive and has provided a variety of technical retrofit possibilities. Many municipalities have investigated the scope and jurisdiction of the soft-story problem. Regional non-profit organizations actively address awareness of multi-residential, soft-story building exposure to earthquake damage.

In May, 2012, FEMA released “Seismic Evaluation and Retrofit of Multi-Unit Wood-Frame Buildings With Weak First Stories” (FEMA P-807). These guidelines address seismic retrofit requirements for weak-story wood-frame buildings in seismically active regions of the United States, but with a particular focus on Northern and Southern California and the Pacific Northwest. These retrofitting guidelines are designed to focus on the weak first story in a building and to provide just enough additional strength to protect the first floor from collapse but not so much as to drive earthquake forces into the upper stories, placing them at risk of collapse. When well-implemented, the guidelines can take into account the building strength provided by existing non-structural walls. FEMA has subsidized technical training through the Applied Technology Council (ATC), the FEMA P-807 report authors, to expedite implementation of the guidelines.

Growing awareness of the vulnerability of multi-residential, soft-story buildings; the possibility of capable and comparatively-affordable retrofit technical solutions; the promulgation of standardized evaluation and implementation guidelines with training materials that address the specific problem; significant probable exposure of mostly non-property owning residents to seismic risk; and, political efforts by municipal authorities and agencies cannot accelerate addressing residential soft-story problems successfully without devising more efficient and equitable financial support strategies beyond traditional mechanisms.

[Since writing, a "Mandatory Soft Story Retrofit Ordinance" was unanimously approved by the Board of Supervisors of the City of San Francisco and will be signed into law by Mayor Ed Lee on April 17, 2013, the 107th Anniversary of the 1906 Great San Francisco Earthquake.]

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