Oakland may soon require hundreds of old apartments to be seismically retrofitted in an effort to prevent a mass collapse of buildings in the next big earthquake.
The retrofit rules would apply to soft-story residential buildings: multiunit, wood-frame structures with weak first stories built before 1991. An apartment with garage parking in the ground floor or street-level retail could fall into the targeted category.
Such buildings are prone to collapse during earthquakes, when the combined weight of shaken upper levels becomes too much for the vulnerable first story, as Loma Prieta proved in 1989 and Northridge in 1994.
“You look at photos of (San Francisco’s) Marina District after ’89 — quite a few buildings looked like three stories when they used to be four,” said Thor Matteson, a structural engineer of the Bay Area firm Quake Bracing.
Oakland is believed to have more than 24,000 housing units in 1,400 to 2,800 soft-story buildings, defined as those with at least five units and two to seven stories, according to city estimates. The first step of the ordinance proposed by City Councilman Dan Kalb and Mayor Libby Schaaf involves finding out which buildings must be retrofitted and which are exempt, such as those that have already completed the work.
Building types would be divided into three tiers, and each category would be on a different timetable. Owners would have four to six years to complete the retrofit work.