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seismic retrofit contractor retrofits an older house

Retrofitting a Home built before 1940

Seismic retrofit contractors such as Bay Area Retrofit mostly do seismic retrofit work on homes built before 1940 that have a structural weakness called a cripple wall.  Homes built on hillsides after 1940 also have cripple walls and their retrofits must be addressed in the exact same way.  At least 95% of the observed damage to homes in previous earthquakes was caused by cripple wall collapse.  Fortunately these same earthquakes proved method seismic retrofits can prevent catastrophic damage.  Without exception these older homes need their cripple bolted to their foundations and braced with plywood.

These homes are found in the older neighborhoods of the Bay Area cities most of Oakland, Berkeley, and smaller cities like Albany, El Cerrito, and Richmond.  These homes are vulnerable because they were built before any seismic protection regulations were part of the building code.  Even newer cities such as San Jose and Fremont have their older neighborhoods where you will find homes with cripple walls that need to be strengthen with cripple wall retrofits.

If you have more than 3 steps leading into your front door it is almost certain you have a cripple wall.  If it collapses it can create a terrible disruption in your life and earthquake insurance cannot protect you against this.  Not only will you need to clean up the mess and be displaced for who knows how long but losing a home has a terrible financial impact.  A retrofit usually costs 1-3% of a home’s value and is probably a good investment relative to the prices of Bay Area homes.
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Seismic retrofit of house without cripple walls.

Retrofits in San Jose, Sunnyvale, Fremont and Nearby Areas Built on Flat Lots

After approximately 1940 houses were no longer built with cripple walls unless they were on a slope.  This is especially true in newer cities such as San Jose, Sunnyvale, Fremont, Burlingame, Walnut Creek, Santa Clara, and practically anywhere where house are built on flat lots; usually as part of a large subdivision.  Foundation bolting has been required in San Jose since 1927, in Fremont since 1956, and everywhere else in the Bay Area since 1958, so if your house is less than fifty years old you can be sure it is bolted.  This does not, however, mean that it would not benefit from a retrofit.

The California Building Code: A Flawed Document

Even if a house is bolted and “built to code,” it is still vulnerable to earthquakes. The California Building Code is a set of guidelines created by building officials, volunteers, and representatives from different agencies in an effort to make sure houses are built to be earthquake resistant. The building code is always changing. It incorporates insights we gain after large earthquakes occur. It also changes as a result of pressure from interest groups, such as the well-funded National Association of Builders (NAB). NAB lobbies to make construction costs as low as possible, sometimes at the cost of seismic safety.
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Emergency carrying a stretcher after an earthquake

When the shaking starts what do you do?

This is a first hand account from interviews with hundreds of earthquake survivors, rather than speculation as found in literature published by the American Red Cross.  The most important thing to stress is that you will be able to enter your home.

While working for the Federal Emergency Management Agency the author observed the the following:

It is not necessary to keep supplies of water and food in a secure area outside of the house.  Unless your house slides down a hill you will be able to enter the house after the earthquake.  You will have at least 40 gallons of water in your water heater which should be plenty until help arrives.  For this reason it is critical that you securely strap your water heater to a wall.

All non-perishable food will be available for the same reason, so it is critical to keep canned food, a can opener, and a camping stove somewhere in the house.  It is also important to keep enough critical  medicines on hand to last you at least two weeks.  Hopefully you are not on dialysis!

The impacted people in your neighborhood will naturally come together after the earthquake as they always do after disasters.  As noted earlier, you will still be able to enter your neighbor’s homes to see if they were injured of if they need anything.  Injuries, sometimes serious, do occur if precautions are not taken to prevent secure objects such as book cases from falling on you.  Best not to sleep next to a tall bookcase. Read more


Soft story home with living area above a garage needing a seismic retrofit

Retrofitting a House with Living Area above the Garage

Homes with living areas above a garage are have something called a “soft story.”  In these homes at the front there is nothing holding up the living area above the garage except 2 narrow walls on either side of the garage door.  These act as posts in earthquakes and can tip over with catastrophic consequences.

Seismic retrofits for soft story buildings are done in several ways.  If the walls on either side of the garage door meet the building code required 4 feet in width standard shear walls are a good option.  If the walls are narrower some companies have invented super shear walls that can be much narrower.  Another approach is to some use a principle called rotation where shear walls are built on the the back and two sides of the garage.  Sometimes a custom made large vertical steel beam is embedded in concrete and attached to the floor above the garage door.  All of these methods work and it is up to the retrofit contractor to figure out which is the best approach.

Bay Area Retrofit usually uses the vertical beam method which will be discussed later on.  It is not only extremely effective but the patent pending system we use is fully serviceable after an earthquake so it can be used again and again.  Prior designs could only be used once, and the mangled and bent pole would need to be removed after the earthquake at great expense.
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Typical hillside home on a foundation with serious earthquake damage hazard

Retrofitting a House Built on a steep Hillside

Home built on steep lots are very dangerous in earthquakes, in fact, they are life threatening.  Damage observed after after the 1994 Northridge earthquake showed that the provisions in the California Building Code designed to protect homes do not work. Los Angeles, Santa Monica, and most of Southern California have developed their own building codes for protecting these homes from earthquakes.  They have also developed their own retrofit building codes, which you should make sure your retrofit contractor or engineer is aware of before hiring them.

After the Northridge Earthquake it was discovered that one house that should have collapsed survived the earthquake just fine.  It turns out a brilliant architect speculated earthquake damage would occur using conventional building codes, so he designed this house with all the components which are now part of the Los Angeles Steep Hillside Home retrofit code.  It is the only retrofit building code that one should even consider.

These retrofits are very expensive, usually costing in the tens of thousands, but certainly a good investment relative to the danger.  The require large steel braces that must be welded, and an analysis of the existing foundation to make sure it can take the force. The steepness of the slope makes working on these homes very difficult.  If you are concerned with your safety, probably best to live somewhere on flat ground.
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Cripple wall retrofit terminology and diagram

A Review of Seismic Retrofit Design and Installation Principles

The information on this website will help you spend your money wisely on an effective retrofit at a reasonable price.  For a well rounded understanding of how the retrofit process works it is important to look at the methods used for retrofitting houses dissimilar to your own.  For example if you live in a houses with a cripple wall, you might have sections that do not have cripple walls, and need to understand how other kinds of retrofits work.  If you live on a steep hillside home, part of the house will require a cripple wall retrofit, part a no-cripple-wall retrofit, and part of it will require a stepped foundation retrofit.

Regardless of how your house was built, understanding how all retrofits work will help you in the decision making process. iI recommend you take the half hour or so needed to study and understand the material before spending thousands of dollars.

Knowledge is power, and the more you know, the better able you will be to evaluate bids from seismic retrofit contractors and engineers. Instead of being at the mercy of a retrofit professional you will be able to speak to them as someone as knowledgeable. if not more knowledgeable, than they are.  I am still learning after 21 years and have condensed my knowledge into this website for the public’s benefit.  Please, if something is not clear let me know at [email protected] so I can address the problem.
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Areas Served

San Jose,Sunnyvale, Fremont,Oakland,Berkeley
And Surrounding Areas
408-664-6355
510-548-1111

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License Info

Works' Comp RWCC64393236
Contractors Lic #558462
Bond #SC6334450
Liability Ins PCA 1045011
Link to Contractor's License Board