By Jessica O’Sullivan, Temblor
I am crouched in the bowels of a two-story home in Berkeley, California, my headlamp lighting up the inhospitable dustiness of the crawlspace as I suspiciously eye the rat-trap to my right.
My day crawling around in sooty basements to talk about seismic retrofits had taught me a couple lessons. It cemented the difficulty and invisible obstacles that homeowners face in finding a reliable contractor. The benefit of hiring a structural engineer, despite the higher price tag, also became crystal clear.I would have never guessed, going into the dark crawlspace, that the retrofit was anything but adequate. I knew a few things – probably more than the typical homeowner – about retrofit (it’s in my job description after all) but I am neither a structural engineer nor a contractor. Going in, the retrofit we were inspecting checked all my mental boxes. There was shear panelling, shiny metal connectors attaching the floor framing to the cripple walls, and equally shiny foundation anchors. The amount of hardware was reassuring.
But the devil is in the details. It turns out that some of that steel hardware was designed for hurricanes, not earthquakes. The floor framing members, called “joists”, were not stabilized with lumber blocks between them; blocks prevent the joists from collapsing to one side or another. Some of the plywood shear walls had too many nails, creating asymmetrical strain in an earthquake. Some of the hardware didn’t have enough bolts. And this was a B-? It begs the question of just how insufficient some of the retrofits he inspected are.
We also visited a Do-It-Yourself seismic retrofit in the area. Thor had created a retrofit plan for the hillside home. The homeowner pointed out where Thor had marked on basement walls with the hardware product number for various bolts and brackets. It was like Ikea instructions for a DIY retrofit—except you need a lot more than a hex wrench.
The homeowner’s workshop revealed his handyman inclinations. There was a line of hard hats across a roof beam, and more screwdrivers than I could count. At the end of the day, the homeowner will have a more reliable retrofit than the previous home we had visited, and it was reassuring to know that DIY was a viable option for those with the time and know-how to undertake the project.
Although many contractors don’t seem to have kept up to speed, there have been sizeable efforts to improve the standard of seismic retrofits. There are resources available to homeowners and contractors. Temblor connects homeowners with qualified retrofitters and structural engineers because we want you to be protected.
Earthquake Strengthening for Vulnerable Homes by Thor Matteson
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