Will Your Home Stand Up to the Bay Area's Next Big Quake?

The formula of what makes a building survive is so variable from house to house, building experts say. Take the test to find out below.

Note: Originally reported in April, we brought this story back for Rohnert Park and Cotati following a series of quakes that hit Berkeley this month. Latest:.

Regional and local building officials say it is nearly impossible to determine how the roof you’re living under will fare during the next big earthquake — which along the Rodgers Creek Fault.

Rohnert Park is built on a series of underground water channels that can cause the land to react like quicksand during an earthquake. To make it worse, Rohnert Park sits on soft soils, which intensify ground shaking.

It's very difficult to assess your home from the naked eye — soils structures are built on can vary drastically from site to site, and cities don’t keep track of when houses were built, or to which building code. The older the house, the greater the risk of collapse. 

Structures that could fail in an earthquake include:

  • Soft story buildings — normally houses or apartment buildings with a garage or business on the bottom that can’t hold up weight during an earthquake. 
  • Single-family homes, which can slip from the foundation because they’re not adequately bolted down, or because walls aren’t reinforced .
  • Older mobile homes, built prior to 1995, which are likely to shift off their support during an earthquake.

Finding Out About Your Home

One way to begin assessing how well your home will do in an earthquake is looking first at the year it was built.

An analysis by Rohnert Park Patch of the city’s housing stock put A, B and C sections at the greatest risk because they’re the oldest. Building records indicate the majority of A section was built from 1958 to 1962, when the city was officially incorporated.

Most of B section was built between 1963 and ‘65, and C section comes in between ’77 and ‘80. Most of G, H, L sections were built in the early 1980s and early ‘90s and M was almost all constructed in the '90s. Sections P, R and S range from 1976 to 1991, but the many of the houses were built in 1976, our analysis shows. 

“Different jurisdictions have more control over their retrofitting than others,” said Michael Whitaker, Santa Rosa’s chief building official, who many local authorities joke is the "guru of building codes."

“It’s really a matter of identifying your building,” Whitaker said.

But, said Danielle Hutchings, the earthquake and hazards program coordinator for the Assocation of Bay Area Governments, it takes a brut force effort to undertake that kind of data collection.

“Volunteers literally walk the streets and visually identify what buildings could collapse, but even then, it could be wrong,” she said.

A quick easy test, from the Association of Bay Area Governments website, can help determine if your home will survive an earthquake. Tally up the points and keep track.

  • Was your home built before 1960? (five points) 1961-1978? (three points) 1979? (one point)
  • How tall is it? Two ore more stories with living area above garage? (five points) Split level or on a hillside? (six points) One story, with three or more steps to the front door? (four points) One story, with less than three steps to the front door? (one point)
  • What intensity does the shaking intensity map show for your neighborhood? Dark red or black? (seven points, and Rohnert Park and Cotati are in the dark red zone, so we needn't go further)

According to ABAG, if you counted 13 points or more, "it probably needs to be evaluated to see if it is strong enough to keep you and your family reasonably safe, unless it has been strengthened in the last few years."

This test for single-family homes varies slightly for apartment buildings. The findings can differ in multi-story buildings depending on what material the walls are built from and if the walls are reinforced. The most important thing to know is when your house was built, if you don't know any of this other information.

Take the full "apartment test" here. Do you live in a mobile home? Take that quick test here.

Shaking and liquefaction during an earthquake cause the most damage. Houses can sink into the ground, tip over, crumble or split in half. But each structure could experience a different level of disaster depending on where it's situated in relation to the fault, how it's built, the type of soil the house is built on and the magnitude of the quake.  

“When I first started in ‘79, the codes were plain and simple,” said Greg Adams, Rohnert Park’s building inspector, who started with the city in January. “But every time there’s a seismic event, they look at where buildings fail and determine what we need to do to not let that happen next time.”

Many houses built prior to the ‘90s wouldn’t meet minimum building code standards today, Adams said. But, to retrofit them would be expensive and time consuming.

“The important thing is that they met code when they were built,” he said. “The code really doesn’t go into retrofitting older houses, it’s more like ‘if you want to retrofit, here’s how.’”

“It’s really up to each resident,” he added.

Glenn Schainblatt, who runs the Cotati and Sebastopol building departments, has spearheaded a campaign in Sebastopol to identify and retrofit vulnerable structures. So far, he’s tallied 55 that need to be retrofitted.

“Anything built prior to the ‘70s really is kind of dicey, it wasn’t really built to code,” Schainblatt said. “But just because they’re old doesn’t mean they’re dangerous — you just never know.”

The law only requires unreinforced masonry buildings, schools, hospitals and government buildings to be retrofitted in what’s called seismic zone four, an indicator that we’re dangerously close to a fault. But it is residences that could absorb the majority of the damage, mostly because statewide building codes only require new development to be built to withstand an large earthquake.

“People need to understand that the buildings code is a minimum standard, so when an earthquake strikes, it’s only required to get you out of the house alive,” said Danielle Hutchings, the earthquake and hazards program coordinator for ABAG. “

“It doesn’t say anything about every being able to get into the house again, that’s why we think most older buildings need to be retrofitted,” Hutchings said.

Editor's note: Are you a Rohnert Park resident who can't find when your house was constructed? We may be able to help.

Leland van den Daele April 14, 2011 at 04:25 AM
After the recent Japan earthquake, we replaced our cement tile roof. More than half our tiles were supported only by rafters. The new roof has an undergirding of plywood and reflective insulation covered by shingles. We made this change because in the Kobe earthquake about two decades ago, houses with tile roofs collapsed under the weight of the tiles. A compounding factor for our house was "rafter only" support for the tiles. The house has poor sheer strength, so if it starts to tilt, the house might fracture. Lots of RP houses still have these 50 year tile roofs. They are attractive and provide good insulation from the sun, but unfortunately they are dangerous in earthquake country, compounded by inadequate support and lack sheer resistance.
Angela Hart April 14, 2011 at 02:45 PM
Wow Leland, that's really interesting — I think it's so crazy that the only way to find out, really, is by having an expensive analysis by an engineer. Thanks for your comment and for sharing what you did to retrofit.
Jason July 25, 2011 at 06:43 PM
Hi Angela, I appreciate your coverage regarding earthquake preparedness in our area. There are options for single family residences to gauge a home's earthquake "readiness" that do not involve the expenses of an engineer or architect. ABAG has posted a document called "Standard Plan Set A" that can be used to evaluate a home and, if needed, guidelines on how to mitigate its weaknesses and increase the likelihood of it withstanding the quake. At this point raising public awareness of the need for consideration is the biggest hurdle to overcome in community earthquake preparedness.
Angela Hart July 25, 2011 at 08:27 PM
That's great to know Jason, thanks for taking time to point that out to me.


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