Some of the most susceptible structures to shaking damage are soft-story apartments and condominiums. A soft-story residential building is one that has open parking or commercial space on the first floor and housing on higher floors built prior to recent codes. In an earthquake, ground shaking causes such structures to sway and sometimes collapse. A soft-story collapse can have particularly disastrous consequences considering that they crush cars and kill people occupying the open areas.
ABAG modeling has shown that, in both a large earthquake on the Hayward or San Andreas faults, two-thirds of the uninhabitable housing units will likely be in soft-story residential buildings.
Estimates of Number of Soft-Story Buildings in the Region
The following table summarizes the number of buildings identified as having a potential soft-story by various building inventories. The year built, units,and stories indicates the criteria used to estimate the number of buildings. More information about the inventories and soft-story mitigation programs in these cities (and others) can be found below the table.
|City/County||Total Buildings||Total Units||Year Built|
|San Francisco||2,800||29,000||< 1973|
|San Francisco (estimated)||4,600||18,400||< 1973|
|San Francisco (estimated)||3,400||10,200||< 1973|
|Oakland (estimated)||370||1,110||< 1991|
|Entire Santa Clara County||2,630||33,119||any|
|San Jose (incl. in county total)||1,093||10,923||any|
|Berkeley||400 (320 wood-frame)||5,000||< 1995|
|Alameda (estimated)||178||2,623||< 1985|
Approximately 140,000 units in 18,000 of these buildings exist in the Bay Area. ABAG (2003) estimates that soft story buildings will account for approximately two-thirds of uninhabitable buildings in a major Hayward fault earthquake, and they represented almost half of the housing lost in the 1989 Loma Prieta earthquake
While they are not the only fragile building type, for some Bay Area jurisdictions, soft story buildings comprise a significant percentage of the residential units. This puts residents, primarily renters, at risk. Protecting soft story buildings from collapse through retrofit saves lives and can prevent community devastation.
Some Bay Area jurisdictions have begun to recognize soft story buildings as a problem and have already developed and adopted policies to inventory, assess, and retrofit these buildings. These regional leaders can help inform other Bay Area jurisdictions by sharing lessons learned, what works and what doesn’t.
For more information or to schedule a free estimate, give us a call today at (408) 785-1343