Broken windows, falling glass in Bay Area’s recent storms raise concerns about building codes

As violent storms beat down on the Bay Area over the last few months, rain hasn’t been the only thing falling from the sky.

Intense winds with gusts over 70 mph wreaked havoc on the region, turning deadly as trees toppled over and landed on cars, roads and homes. And in San Francisco, windows cracked on at least six high rises, with some panes breaking completely, hurling shards of glass to the ground.

The shatterings prompted the city to trigger several shelter-in-place orders. Department of Building Inspection Assistant Director Christine Gasparac said they’ve issued violation notices to the properties that had broken windows, giving building owners 14 days to provide the city with engineering reports on the windows.

Windows breaking due to strong winds is supposed to be rare in this region, according to Megan Stringer, president of the Structural Engineers Association of Northern California. But because it happened in several buildings, it has engineers across the Bay Area searching to determine whether other cities could face the same problems.

The window failures could have been caused by a number of things, from design flaws to flying debris, said Stringer, an associate principal at Holmes Structures, the engineering firm behind Adobe’s north tower in San Jose and NVIDIA’s campus in Santa Clara.

“We don’t know if all of the failures are happening because of the same reason, or if all of them are happening for very different reasons,” she said. “Once we figure out what they are, we have to see if they can be detected by any kind of realistic inspections and then we can better understand the extent of the problems and what the next steps should be.”

Stringer added that some of the engineers from the Structural Engineers Association of Northern California are involved in writing the “wind code” for the next building code cycle, and are specifically looking into what happened in San Francisco — and if metrics need to be changed statewide.

In California, many windows are designed to withstand 90 to 110 mph winds.

While other Bay Area high rises dwarf in comparison to those in San Francisco — the Salesforce Tower currently tops out as the tallest building in the city at 1,070 feet — height may not be a major factor in why the windows are breaking.

In San Jose, the tallest buildings are the Miro Towers at 298 feet, and in Oakland, the tallest structure is the Ordway Building at 404 feet.

According to Dan Devlin, a principal at structural engineering firm Biggs Cardosa Associates, lower high rises like these could suffer the same problems if a mistake is made in design or construction.

But even if everything is executed perfectly, severe windstorms like the ones that hit the Bay Area the last several months may test the limits of California’s regulations.

“Even if everything was done correctly, we just don’t design for the highest wind speed we ever expect,” Devlin said. “We design for something that happens rarely, but not a wind that is inconceivable.”

In San Jose, planning officials said broken windows from strong winds aren’t a concern since the city follows state building codes.

“Building safety is the underlying concern of our building permit operations and we take it seriously,” said Cheryl Wessling, the spokesperson for the department of planning, building and code enforcement. “Window failure in high rises during windy weather events has not been a problem in San Jose, and to our knowledge, there’s not been such an incident in San Jose.”