In an earthquake, the biggest risk to the most homes with the greatest potential for costly damage is where the house’s framing meets the foundation.
While changes in Portland’s city code show that nobody cared about that until recent decades, earthquake awareness is ramping up business for seismic retrofitting contractors in Portland.
Good Energy Retrofit is a Portland-based, MWESB-certified seismic retrofit contractor. "We have definitely seen an increase in demand for seismic work over the last year, and general Cascadia Quake awareness has increased dramatically. Seismic work be about 50 percent of our business this year, when it was about 20 percent in previous years past. You could probably say my seismic work has tripled," Grube said.
...[Good Energy Retrofits] does complete seismic retrofits, which connects the concrete foundation to the wooden structure of the house.
If a house is not bolted to the foundation, it’s at risk of bouncing or sliding right off.
"When this happens, the likelihood of a house requiring demolition increases dramatically. If a house can simply stay connected to the foundation during an earthquake, then there is a possibility of doing repairs on the house without having to proceed to total demolition — not to mention that a life might be saved," Grube said.
The second-highest concern is houses with cripple walls, or short walls built between the poured foundation and the first floor. "These walls are very vulnerable parts of a house in an earthquake, and it’s relatively easy to shore them up, I think that name must have come from the fact that in an earthquake, these walls simply buckle, crippling the house," Grube said.
Bolting the house to the foundation wasn’t in Portland’s city code until 1976. Bolting isn’t considered new-build seismic code, but it wasn’t until 1995 that Portland adopted real seismic codes, which have been systematically updated as recently as 2015.
According to the city, this is a danger that applies to about 100,000 homes built before 1974 that are vulnerable to structural failure in the event of an earthquake.
...The city allocated $500,000 in federal funding to seismic strengthening, through the Federal Emergency Management Agency and in partnership with nonprofit Enhabit. The funds helped reinforce 150 homes.
"Basically, engineering guidelines have been created to address the most common seismic vulnerabilities in a home, and the most potentially damaging to the greatest number of homes. It’s a great thing that the city has brought this option to Portland, as it makes basic seismic retrofit affordable and accessible for Portland homeowners," Grube said.
It’s part of Oregon’s resilience plan to reduce risk and improve recovery in the event of the next Cascadia earthquake and tsunami, penned in 2013 by the Oregon Seismic Safety Policy Advisory Committee.
"In this approach, a house has to meet specific existing structural guidelines for this pathway to be appropriate. Anything else needs custom engineering, and we refer that out," Grube said.
Good Energy Retrofit
...“Doing basic seismic retrofits simply completes my whole-house approach to caring for old homes. When I assess a home, I look at the energy-related components such as insulation, air leakage, heating and water heating efficiency, but I also look at issues related to the home’s durability, safety and indoor air quality,” Grube said.
Read the original post from the Portland Tribune.