Bay Area cities lag in making housing quake-safe

cities also have conducted detailed seismic assessments of their school buildings.

Hospitals, meanwhile, are expensive to retrofit, and many have lagged behind state deadlines for major repair work. Several San Francisco hospitals are undergoing retrofit work or plan to complete it no later than 2015. San Francisco General Hospital, for instance, will be replaced in the coming years.

The housing risk looms large, though

Unsafe construction

Selna notes that two building types are of particular concern to engineers: wood-frame, “soft-story” buildings and concrete-frame structures that lack sufficient steel reinforcement.

The thousands of soft-story buildings in San Francisco include the classic apartment building with a store or restaurant on the first floor, as well as the Sunset District home built over a garage. They feature a space — a glass window or a garage door — on the ground floor where a wall might otherwise be, making their wood frames prone to twisting and buckling in an earthquake.

About 120 such buildings were damaged in Loma Prieta. Engineers say that destruction could be 100 times worse after the big temblor that scientists say has a more than 60 percent chance of hitting the Bay Area within the next three decades.

Also at risk are precarious concrete-frame structures erected before building code changes in the mid-1970s. Those changes demanded more steel reinforcement in and around beams and columns and stronger walls. They include everything from Nob Hill condominiums to former printing houses.

Among Bay Area cities, Berkeley has done the most to encourage soft-story building owners to retrofit. Among other things, the city requires owners to get an engineering study to identify retrofit solutions and costs. Landlords must post warning signs if deficiencies are confirmed.

In San Francisco, a city-sponsored report in February recommended mandatory retrofits for about 2,800 of the city’s largest soft-story buildings — those have three stories or more, at least five residential units, and are considered to be the most dangerous.

Voluntary retrofits

Almost 100,000 more soft-story buildings are in the city, such as the homes built over garages in the Sunset District. In September, Mayor Gavin Newsom introduced legislation to encourage property owners to voluntarily retrofit the buildings, including expediting the permit process and waiving fees. Newsom directed the city’s Department of Building Inspection in February to craft a law requiring soft-story retrofits, and he has said that a task force will be convened to make recommendations about how to design and implement the program.

Consultants hired by the city building department plan to provide recommendations regarding the dangerous concrete buildings in coming months.

Quake resources

Only a handful of cities have provided even basic information or minimal incentives to help owners retrofit their properties. Although most experts agree that mandatory programs are the only way to ensure widespread retrofits, such mandates are just now being considered.

Risky types of buildings
  • Soft-story: San Francisco has identified 2,800 soft-story buildings that are the most dangerous. They have three stories or more, at least five residential units and large ground-floor openings.
    • Retrofits include adding plywood shear walls, steel frames and columns
    • Cost to retrofit: $9,000 to $28,000 per residential unit
    • Potential quake damage that could be prevented by retrofitting: $1.5 billion
  • Concrete-frame: Engineers estimate that there are several hundred in San Francisco. They are dangerous because they lack steel reinforcement in beams and columns. San Francisco-sponsored studies on these structures are expected in the coming months.
    • Lack of steel in columns causes them to crumble or explode under seismic pressure
    • Collapsed in big earthquakes in Northridge (Los Angeles County), Mexico, Japan and Turkey
    • Retrofits include wrapping columns with steel rebar or carbon fiber or adding steel braces.