Naomi O. Miroglio
AIA, Assoc. DBIA
The 6.0 magnitude earthquake that hit Napa in 2014 could have been a lot worse. Fortunately, the earthquake struck at 3:20am, when the sidewalks of downtown were deserted. No lives were lost, and most of the historic masonry buildings held up structurally. However, the quake was a wake-up call for the historic preservation community, and there are lessons to be learned.
On the morning of the earthquake, I got a call from Tom Blackwood, director of retail operations for Buena Vista Winery. It was just two years ago that we completed a renovation of the historic winery buildings, including seismic retrofitting of the Champagne Cellars at Buena Vista, a California Historic Landmark that dates back to 1857. It had been closed since the 1989 Loma Prieta earthquake. To retrofit the building, we used center core drilling, a technique that reinforces the structure without visibly altering the exterior.
When Tom called, he said he was getting phone calls from people saying that rocks had fallen. “I don’t know what to tell them,” he said to me. “Do you think the buildings are safe?” So I went to take a look. The “rocks” turned out to be the size of pebbles, for the most part. The building did experience some movement, but the only damage was minor and cosmetic, the kind that you would expect in an earthquake of this magnitude. That was a huge relief.
I visited the other historic buildings we’ve worked on in Napa, and they also performed well—the seismic retrofits did what they were supposed to, although in some cases there was more cosmetic damage than we had expected.
Not every historic building in Napa fared as well as ours did, however—even some that had had seismic upgrades. Engineers are performing analyses to figure out why. We learn something from every earthquake—it isn’t an exact science.
But because of the damage, there are concerns among the public that older unreinforced masonry buildings, even if they’ve been retrofitted, might not be safe. It would be a shame if these fears made municipalities and owners of historic properties less prone to save historic treasures.
In the 1970s, seismic retrofits tended to be overdesigned. Historic preservation architects have tended to view overdesigned systems as negatively impacting historic structures because in many cases, the anchorage plates are visible. If you tour the Buena Vista Winery, you can see the anchor plates that were put onto the press house in the 1970s, whereas with the retrofit of the champagne cellars, which we were involved with, the reinforcing is invisible. Both of these strategies worked for Buena Vista. But perhaps anchor plates could have done a better job of limiting damage to some of the other historic buildings in Napa. Maybe it’s time to rethink anchor plates and make them more aesthetically appealing. To obtain historic tax credits, it’s difficult to get an anchor plate solution approved, but that might need to change.
Life safety is the goal of a seismic upgrade. But there are many different kinds of seismic upgrades, and a variety of levels of upgrade as well. Some owners of historic buildings choose less costly solutions, which might not hold up well in a strong quake.
In 1986, a state law was passed requiring local governments to identify unreinforced masonry buildings and establish a program to reduce the risks. Some jurisdictions adopted mandatory programs, requiring owners of these structures to retrofit them by a specific date or face penalties. St. Helena, just northwest of Napa, made it mandatory for owners of unreinforced masonry buildings to retrofit, and historic buildings there performed well—of course, St. Helena was farther away from the quake’s epicenter and experienced less intense shaking.
It may seem a no-brainer for every municipality to adopt a mandatory program, but not every community has the resources—in an economically challenged downtown, the buildings don’t have enough value for the owners to borrow enough against them to pay for full-fledged retrofits. Requiring owners to seismically reinforce their historic buildings might lead unintentionally to the demolition of these treasures instead of their rescue. Back in 2005, Napa made compliance with its unreinforced masonry ordinance voluntary because of this very concern.
We need to be more creative about helping offer financing to help owners of historic buildings upgrade their properties. These buildings contribute to the public good, and we will all win if we come up with strategies to protect them from our state’s sometimes-volatile tectonics.