Seismic experts are raising alarms about “soft-story” homes saying the style is vulnerable to collapse in an earthquake and needs retrofits.
Soft-story homes, or single-family houses with living spaces above the garage, risk collapse because thin supports hold the heavy living space. The structure can collapse if the supports on either side of a garage door bend or break during an earthquake.
The risk is similar to apartment buildings built with carports or garages on the ground floor, held up by weak columns.
Experts say dwellings built before 2000 are vulnerable. Construction codes changed after earthquakes in 1989 and 1994, so soft-story homes built in 2000 or later are presumed to be up to current earthquake standards.
“If they have full collapse, that’s an 8- or 9-foot drop. … The house is dropping with all the furniture flying around in it,” structural engineer Janiele Maffei, chief mitigation officer with the California Earthquake Authority, told the Los Angeles Times.
“It’s just really serious, and [could result in] hundreds of thousands of dollars worth of damage. It could be a total loss as well,” Maffei said to the Times.
Other types of California homes are also vulnerable to earthquake damage. These include homes built before 1979 with a handful of steps above the ground and mobile homes.
Homes built before 1979 with a handful of steps above the ground are vulnerable to collapse because they are attached to the foundation by a short, flimsy wall known as a “cripple wall.”
Meanwhile, mobile homes are vulnerable to collapse because they are not anchored to the ground.
RETROFIT Costs
The retrofit of a cripple wall costs around $5,000 in Southern California and $6,000 in Northern California, according to reports.
Retrofitting soft-story homes costs considerably more: $14,000 to $28,000, according to reports. But the process has become more straightforward — and perhaps cheaper recently.
The Federal Emergency Management Agency published pre-engineered retrofit plans in October 2019. Those plans allow many homeowners to implement seismic strengthening on soft-story houses without a structural engineer—a potential savings of a couple of thousand dollars.
