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California has two-thirds of our nation's earthquake risk. Structures(external link) that lack adequate sill plate bolting (external link)and cripple-wall bracing(external link) are more susceptible to earthquake damage.

The frames of older houses are often not bolted to their foundations, and their cripple walls(external link) may lack bracing. Houses without adequate bolting and bracing(external link) can slide or topple off their foundation during an earthquake, requiring potentially very expensive repairs. But this serious damage can be prevented with a proper seismic retrofit.

There is no such thing as an “earthquake-proof structure.” But there are straightforward measures that will likely reduce the potential for (or severity of) earthquake damage(external link). The California Existing Building Code (CEBC)(external link) states that its retrofit provisions are "minimum standards intended to improve the seismic performance of residential buildings; however, they will not necessarily prevent earthquake damage."

How your house is built and its foundation type determine what type of retrofit your house needs. Houses with a raised concrete perimeter foundation that lack sill plate anchors(external link) and/or cripple wall bracing(external link) may follow existing state building code (CEBC, Appendix Chapter A3) or standard plan sets, which also provide step-by-step directions. 

The following types of houses may require an engineer to design a retrofit:

• Soft-story row houses
• Houses on hillsides
• Houses with living space over the garage
• Post and pier foundation houses

If your single-family house:

• Was built before 1979,
  
  
• Is on a raised foundation, and
  
  
• You've completed an earthquake retrofit, and a licensed contractor(external link) or structural engineer(external link) has signed the Dwelling Retrofit Verification Form (PDF)(external link), stating the retrofit is in accordance with required standards.

If your mobilehome:

• Has been reinforced by an earthquake-resistant bracing system certified by the California Department of Housing and Community Development (HCD).