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 What is seismic retrofitting?
How much does retrofitting help?
How much does a retrofit cost?
Do newer homes need reinforcement?
What if I have an older home?
Do I need a contractor, an engineer or an architect?
How can I know whom to choose?
What is seismic retrofitting?
During an earthquake the ground shakes violently. This back-and-forth motion can cause a building to fall off its foundation, resulting in major
damage to the structure and sometimes even total collapse of the building. Seismic retrofitting focuses on strengthening the house-to-foundation
connections using specially designed hardware and engineered construction methods. Retrofitting allows a house to withstand much greater earthquake forces with much less structural damage.
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How much does retrofitting help?
See the true life story at the A True Story button. It is about two identical
houses, one retrofitted and the other not and how they fared in the Loma Prieta earthquake.
Studies by the Association of Bay Area Governments show that a properly
retrofitted home is almost one thousand percent (1000%) more resistant to earthquake damage than one that is not retrofitted. Since earthquakes and
the forces generated by them are unpredictable, seismic retrofitting cannot guarantee a house will receive no damage at all. However, it has been
proven that seismic retrofitting greatly reduces the amount of damage a house receives and is highly effective in preventing catastrophic damage. In fact,
insurance professionals advise homeowners to retrofit first...then get earthquake insurance. Several insurance companies won´t even provide earthquake insurance unless a house has been retrofitted. See graph below.
This graph represents expected damage to homes located in zones IX and X on ABAG´s Earthquake Hazard Maps
According to ABAG, of the Bay Area's older single-family homes (built before 1940) located in Zone X that have not been retrofitted, 20% will
become uninhabitable when a major earthquake hits. Of the older single- family homes in Zone X that have been retrofitted, ABAG estimates only 2% will become uninhabitable.
ABAG estimates 10% of the Bay Area's newer single-family homes (built after 1940) located in Zone X that have not been retrofitted, will become
uninhabitable when a major earthquake hits. Of the newer single-family retrofitted homes located in Zone X that have been retrofitted, ABAG estimates only 1% will become uninhabitable.
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How much does a retrofit cost?
Though it can vary greatly, a seismic retrofit generally costs between 1% and 3% of a home´s value. For many homeowners the one-time cost of a
retrofit equals two to four years of earthquake insurance. And insurance won't prevent or reduce damage to your home...retrofitting will! For more information, see our page on Earthquake Insurance.
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Do newer homes need seismic reinforcement?
Modern building codes have been written so that newer homes usually don't need to be seismically reinforced if they were properly constructed.
However, builders sometimes do not understand provisions of the code that are specific to earthquake reinforcement and neglect to follow these aspects
of the building code. Special hardware has been developed to add greater strength to newer homes and compensate for possible builder's oversights.
Usually retrofits of newer homes are simple and inexpensive.
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What if I have an older home?
Older houses are especially susceptible to earthquake damage because they were built before homes were required by law to be earthquake-resistant.
They are therefore prime candidates for retrofitting. All retrofit building codes, and most retrofit hardware, have been designed for older homes.
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Do I need a contractor, an engineer or an architect?
Generally, architects do not design retrofits; this is something done by structural or civil engineers. As in other fields, engineers tend to specialize,
so if you choose to work with an engineer be sure it is one with special training in retrofit design. Contractors who have had special training in
retrofit engineering principles can also design a retrofit. These engineer- trained contractors are often the best choice. Not only do they understand
the design principles, but they also understand the most practical and cost-effective ways to achieve maximum protection from earthquakes. In
almost every case, an engineer-trained contactor will design a retrofit equal to that of an engineer but at a much more affordable price.
Howard Cook of Bay Area Retrofit is an engineer-trained contractor. He works as a Residential Earthquake Damage Inspector for FEMA and is a triple graduate of the course "Principles of Seismic Retrofitting for Engineers
, Contractors, and Building Officials," sponsored by ABAG and FEMA. Howard has also taken advanced instruction in seismic retrofitting principles
from the leading structural engineers in this field and regularly consults with structural and seismic engineers.
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How can I know whom to choose?
Seismic retrofit technology is continually evolving, and a retrofit contractor needs to understand and follow the most current seismic retrofit standards.
It is also important that he have at least one structural engineer with whom he has a good working relationship. In addition to customer references who
can tell you whether he was on time, cleaned up after the job, etc., he should also have professional references such as engineers, building officials,
and architects who can attest to his competency in the field of retrofit. Call these references to ask about their experiences with the contractor.
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