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/// Nature’s Fury /// SEISMIC RETROFIT T


HE CALIFORNIA EMER- GENCY Management Agency made some in- teresting observations re- cently about how people in high-risk areas respond


to earthquake hazards. “More than 60% of Californians have learned what sup- plies and equipment to have, and how to make their home contents safe, but less than 35% have learned how to make their home structure safer or how to safeguard their fi nances.” As organizations such as the Institute


for Building and Home Safety (IBHS) point out, the potential fi nancial savings from even minor prepping a home for earth- quakes is about $25,000. The three most important upgrades:


A BOLT OR “PLATE” THE HOME TO ITS FOUNDATION


Many older homes lack bolted connection to the ground. Whenever possible, upgrade ½” anchor bolts to ¾” bolts with large wash- ers (square ones are best) at 4’ intervals on the perimeter, and 6’ intervals for interior walls (assuming they rest over foundation walls). If adding bolts is impractical, a plate system that anchors the sill to the foun- dation is a good workaround. Many old homes are simply sitting on a foundation or nailed down with concrete nails. Note that these measures also help secure the home against wind and fl ooding events.


B SECURE CRIPPLE WALLS Short cripple walls often buckle and col- lapse during an earthquake, causing the rest of the house to collapse. Adding a layer of 3/8” plywood to the interior side that ties


Concrete foundation


sill plates all the way to the underside of the fi rst fl oor adds a lot of shear strength. In warm climates, where crawlspace ven- tilation is a concern, holes can be drilled in the plywood panel and covered with insect screen.


C ATTACH RIM JOIST TO SILLS WITH METAL PLATES


The connection between the sill that sits on the foundation and the house frame is a common failure point during seismic events. By simply adding 90-degree metal reinforcing plates around the perimeter of the home, you can greatly improve its resistance to lifting and racking.


Also, studies have shown that most in-


juries in homes tend to be caused by fall- ing objects than structural failures. Strap down heavy objects such as water heaters, air conditioners or tall shelves that could fall or move during a quake event. GB


Plywood shear


panel with screened vent holes


Cripple wall


B A


¾” Anchor bolts at 4’ intervals (or less) on perimeter


Anchor sill to rim with metal plates at 24” intervals


Metal plates where anchor bolts are not practical


C


PART THREE


45


Preparing an older home for future earthquakes is often prudent and relatively aff ordable—yet many homeowners prefer to take their chances.


www.greenbuildermag.com 06.2012


IMAGE: SEISMICSAFETY.COM


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