Standard Plan Sets

Residential Seismic Strengthening Plans

CALBO is promoting for the first time a regional standard for retrofitting single family homes, making them more resistant to earthquake damage. Even though it is well documented that when wood-framed residences are exposed to violent shaking, as in an earthquake, they can literally fall off their foundations, only a third of Bay Area homes have been retrofitted. The standard directly addresses one of the major reasons why homeowners do not retrofit: they do not know what to do and how to go about it cost effectively.

This basic retrofitting blueprint (called a Standard Plan Set) gives homeowners, cities, counties, contractors, and building departments a “nuts and bolts” prescriptive for strengthening homes that will also address the problems of overly expensive and inadequate retrofitting.

"This plan addresses the fact that older single family homes are generally not properly bolted to their foundations or their outside walls (“cripple walls”) are inadequately braced. These are conditions that can be fixed by retrofitting.” The plan covers bolting or anchoring “mud sills” to foundations, adding plywood panels to the inside walls of crawl spaces (“cripple walls”), and attaching the home’s floor to these “cripple walls.” The plan can be used by homeowners in obtaining quotes for retrofitting, by contractors when obtaining building permits, and by cities and counties as a basis for a minimum prescriptive retrofit standard.

This strengthening plan was under development for two years by an expert committee representing ABAG’s Earthquake Program, the International Code Council (ICC) Tri-Chapters (East Bay, Peninsula, and Monterey Bay), the Structural Engineers Association of Northern California (SEANOC) Existing Buildings, the California Building Officials (CALBO), the Earthquake Engineering Research Institute (EERI) Northern California Chapter, and building contractors specializing in home retrofit. Jeanne Perkins, ABAG’s committee representative, and William Schock, the committee chair and Building Official for San Leandro, formally unveiled this Standard Plan Set at ABAG’s Executive Board meeting November 18th, 2004, and in Resolution form endorsed “Standard Plan A: Residential Seismic Strengthening Plan as a prescriptive seismic strengthening plan for cripple wall bracing and foundation sill plate anchorage of light wood-framed residential structures not more than stories in height and containing not more than two dwelling units."

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