More than one out of every seven homes in Mountain View may be vulnerable to collapse in a major earthquake, a nearly five-fold increase over the city's previous estimates, according to a study released last month.

The survey of so-called "soft story" structures found that 488 buildings -- most of which are residential -- containing a total of 5,123 housing units are suspected of having structural vulnerabilities that, in the event of a quake, could cause the buildings to collapse. This makes up nearly 16 percent of the city's housing stock, which is slightly higher than San Francisco (14 percent) and Oakland (15 percent), and significantly higher than Palo Alto at 10 percent.

The commissioned study has been in the pipeline for years, and City Council members are planning to weigh in on whether to pursue a voluntary or mandatory citywide retrofit program, joining a growing number of California cities that have sought to safeguard residents.

Soft-story structures typically have a ground floor that's open on one or more sides for parking and commercial uses, and are vulnerable to the lateral back-and-forth motions of an earthquake, putting them at risk of "pancaking" if the first floor collapses. The vast majority of Mountain View's soft-story structures are two- and three-story housing with parking stalls tucked underneath.

The city's potentially hazardous housing belongs to a subset of buildings with three or more housing units, built with wood-frame construction between 1950 and 1980. It was a popular building style at the time, prior to major earthquakes that showed the destructive damage that could occur. The inadequate first-floor support is a recipe for "excessive lateral and torsional deformation," according to the study, which can cause the building to collapse, causing "deaths and injuries, a total financial loss, damage to adjacent properties and forced relocation for surviving tenants."

The numbers cited in the new 43-page report are significantly higher than prior estimates cited in Mountain View's 2015-23 housing element report, which relied on survey data collected by San Jose State University in 2003. The university refused to disclose the granular survey data, including specific addresses, but stated that there were an estimated 111 soft story buildings containing 1,129 units -- roughly 7 percent of the city's multi-family residential housing.

The university's technique for surveying buildings prone to collapse in 17 Bay Area cities was "ahead of its time" back in 2003, but had a clear tendency to undercount potentially vulnerable buildings, according to the new report. The same university study found that there were 130 soft-story buildings in Palo Alto, but that number turned out to be closer to 300 in a subsequent count.

City staff knew that San Jose State's study was likely inaccurate. The study was conducted in 2003 by college students who had to make judgment calls from sidewalks and couldn't encroach on private property, making it difficult to accurately assess which buildings might have structural deficiencies, according to Shellie Woodworth, Mountain View's chief building official. The more recent study, on the other hand, was done by prolific structural engineer David Bonowitz who had access to the city's database of multi-family residential properties and could view the parcels from multiple points.

Although the number of properties isn't expect to fluctuate wildly again, city staffers are reluctant to publicize the list of addresses, in part because some of the identified properties may turn out to be safe even though they have the appearance of a soft-story structure, Woodworth said.

"There is the potential to prove that it's not a soft story with a licensed structural engineer," she said.

The Voice has sent a formal request for the full list of addresses identified in the report as potentially hazardous buildings.

The largest concentration of soft-story buildings identified are in the city's "Central/Downtown" planning area. It includes the Old Mountain View and Shoreline West neighborhoods, with 132 soft-story buildings containing 844 housing units. The next highest concentration is in the Miramonte and Springer area, which includes several southwestern neighborhoods of Mountain View and Cuesta Park, and reportedly has 67 soft-story residential buildings totaling 667 units.

The popular soft-story building designs were built prior to 1978, when the building code was updated to address the structural deficiencies, but they still make up a huge number of homes in the Bay Area -- approximately 140,000 units across 18,000 buildings, according to a report by the Association of Bay Area Governments (ABAG).

"ABAG estimates that soft story buildings could account for approximately two-thirds of uninhabitable buildings following a major Hayward fault earthquake," according to a 2016 report. "Almost half of the housing lost in the Loma Prieta earthquake was soft story construction."

A path to safety

Now that the city of Mountain View has a firm grasp of how many homes are at risk of collapse, the big question is what to do about it. The City Council could choose to impose a voluntary retrofit program of seismic upgrades, or make it mandatory.

Voluntary retrofit programs are pretty rare and would need to provide a lot of incentives -- including subsidies and tax rebates -- in order to encourage property owners to make the investment. It would also need to come with a strong tracking system for compliance and specific criteria to ensure retrofits aren't just doing the bare minimum for seismic safety.

The growing consensus among California cities is that mandatory retrofit programs are both "preferable and feasible," according to the study. Cities like San Francisco and Berkeley started with voluntary programs only to replace them with mandatory requirements for seismic upgrades soon after. Although the study lists pros and cons for both options, it doesn't mince words on which one makes a real difference.

"Substantial citywide risk reduction comes only from mandatory retrofit programs, not from mandatory evaluation or from voluntary retrofit," the study states.

In the case of San Francisco, which has 10 times as many soft-story units as Mountain View, its voluntary program gave weak financial incentives for building owners to retrofit buildings for earthquake safety. A 2013 report by the San Francisco Public Press found that only 53 building owners had completed retrofits under the voluntary initiative, an average rate of 15 projects each year, putting the city on pace to retrofit all the potentially hazardous buildings in a couple centuries.

Mountain View officials will also need to set a clear scope for a soft-story retrofit program, including a cutoff for building age, height and number of residential units. Cities with mandatory programs generally include all buildings built before 1978 with two or more stories and five or more residential units, with a few exceptions. The retrofit program in Los Angeles includes non-residential and residential buildings, but has an exception carved out for housing with fewer than four units.

There's no engineering- or risk-based rationale behind the unit cutoff, according to the study, with many cities adopting scopes simply based on previous seismic safety programs. Another reason is differing investing and lending practices between multi-family housing with five or more units compared to smaller housing developments, the former being considered commercial real estate.

Three- and four-unit residential buildings make up 30 percent of the potentially dangerous housing, but only 10 percent of the total units in the report, meaning excluding smaller buildings wouldn't put a huge dent in the retrofit program's effectiveness.

Woodworth said it's up to the council to decide whether to make seismic retrofits mandatory, but she said an increasing number of cities in California are making it a priority to retrofit dangerous residential properties as a public safety measure, particularly for buildings with multiple families who can't do seismic upgrades on their own and are at risk of displacement if the building collapses.

"It's coming to light in communities overall in the state," she said. "It would make sense to do something like this, but again it's whether the council wants to make that the priority."

Who pays?

Best estimates show that landlords in Mountain View would have to pay a hefty amount out of pocket for retrofit work required under a mandatory citywide program. One San Jose report estimated it would cost between $9,000 to $20,000 per unit, while the Mountain View study projects a total cost range of $25,000 to $100,000 per building. That leaves city officials with a tough political and legal question: How much of those costs should be passed on to the tenants?

Assuming the city moves forward with a retrofit program, it will be up to the Rental Housing Committee to decide critical issues on how much of the capital costs can be "passed through" to tenants, the extent that retrofit costs can bump up monthly rent, and whether landlords would be on the hook for temporary tenant displacement during retrofit work.

In San Francisco, 100 percent of the retrofit costs can be passed on to tenants over the course of 20 years, but the monthly increase to rent is capped at $30 per year or 10 percent of the base rent.

Los Angeles took a softer approach, with a 50 percent pass-through policy and a cap on monthly rent increases at $38.

The Mountain View study, using a hypothetical $65,000 in retrofit costs and a range of building sizes and pass-through rates, concluded that the city's renters could expect a rent increase between $15 and $78 per month.

Multiple legal questions still remain unanswered, however. The city attorney's office has yet to weigh in on whether retrofit work is considered a capital improvement or a correction to an "unacceptable or substandard housing condition," which could have implications on the city's pass-through policy under the Community Stabilization and Fair Rent Act (CSFRA). The law is also murky with regards to temporary loss of housing services during retrofit work, and whether tenants would be eligible for compensation or a rent reduction if they lose access to parking, storage spaces and other resources that are out of commission for seismic work.

Rental Housing Committee member Matt Grunewald said he wasn't prepared to take a stance on the pass-through question quite yet, and said he would look for the precedent set in cities like San Francisco when it comes to cost-sharing, rental increase limits and amortization periods.

"I would find the benchmark set by other jurisdictions," he said. "Especially when it comes to developing policy for a new law."

Grunewald, who owns a rental property in San Francisco and had to retrofit his building under the city's mandatory program, said his tenants had recently moved in and were already paying market rate, meaning he essentially had to absorb the costs of the retrofit work. He cautioned that the price for coming into compliance and the time it takes to complete the improvements depends heavily on the market, and no construction company is eager for work right now.

"It is really difficult to find companies that have the time and bandwidth to do this right now, and the costs are at a premium," he said.

The study can be downloaded from the city website at tinyurl.com/mvretrofit1.