Questions and Answers about Earthquake Retrofitting and Seismic Strengthening
Questions with Answers
How do I know if I need to Bolt my House to the Foundation?
If there is a large earthquake somewhere in the Bay Area you need a seismic retrofit. Even new houses need retrofits because a deficiency in the building code neglects to address a very serious foundation connection. The Northridge earthquake was caused by an earthquake fault no one even knew existed. There are a few clues that will give you a good idea whether or not you need a seismic retrofit. Age of the house is very important. We do not see foundation bolts in houses built before 1958 though remarkably the City of San Jose has required their use since 1927. If you have a few steps leading into your front door you probably need the cripple walls braced to keep this wall that supports your floor from collapsing. Houses that have been bolted and otherwise braced to remain on their foundations sustain minimal damage.
The way it was built is also very important. Houses on hillsides have very distinct problems that cannot use normal retrofit methods. When a house is part two story and part one story each story shakes at a different rate and will tend to come apart where they are attached. Houses with soft story conditions will have a living area above the garage and require the services of a structural engineer who specializes in soft story retrofits.
Ultimately you will need an evaluation by someone who understands how various homes have performed in previous earthquakes. The amount of information is vast so do your homework and make sure you will be having your retrofit done by a professional who does this everyday. The information on this website will help you determine if your safety and the safety of your home can be entrusted in someone else’s hands.
Will seismic strengthening increase the value of my home?
It depends on the buyer. About one-third of the retrofits we perform are for newly purchased homes. For these people it is important and your home will be more valuable to them; for everyone else, probably not.
Can I do my own Seismic Upgrade and what Tools will I need ?
Why not? But you do need to be aware it is a very complex subject and requires expensive specialized tools for proper foundation bolting. Shear walls are a component of many retrofits and an 180 page book on how to build them proves how complicated they can be. One purpose of this website is to provide homeowners enough information so they can evaluate bids from other contractors and if they want to, provide as much information as possible for someone to retrofit their own home.
Do I need a Structural Engineer to Provide Plans?
An engineer is a must if you are doing a soft story retrofit, but otherwise not very important so long as your hire a contractor who understands the engineering. A knowledgeable contractor can design his own plans and implement them for a single price. If an engineer is used you will need to pay him several thousand dollars for a retrofit design without knowing if you can afford it. In other words, you may pay the engineer for something you cannot use. Better to get a bid from a seismic retrofit contractor who can give you a bid at the start that includes both the retrofit construction and the engineering. One problem with engineers is that most have very little experience. Very few engineers do this kind of work because the pay is low, no one likes to crawl under houses, and the liability is high. This article on the relative seismic design capabilities of structural engineers is an eye opener.
My house did just fine in the Loma Prieta earthquake in 1989. If it survived that earthquake why should I bother?
That earthquake was 60 miles from the East Bay and was not considered the “Big One”. Shaking intensity increases 30 times for every increase in the Richter scale. Loma Prieta was a 6.9 on the San Andreas Fault so when the big one hits here you need to be ready for your house to shake 30 times more intensely that it did on that day. Damage from that earthquake radiated away from the fault so that the homes closest to the fault sustained the most damage. Because of proximity when the magnitude 7 earthquake hits on the Hayward Fault, Berkeley and Oakland can expect very intense shaking and considerable structural damage because these cities straddle the fault line. There may even be faults in the area that we are not aware of such as the one that caused the Northridge Earthquake Fault in Los Angeles.
How large an earthquake will my retrofitted home survive?
We do our best to make sure your retrofit meets the basic design requirements of the California Existing Building Code. We assume geologists accurately inform the code writers how large an earthquake they should expect and we design accordingly.
Is a seismic retrofit an all or nothing enterprise?
Sometimes we feel like financial counselors, earthquake phobia therapists, seismic engineers, and earthquake retrofit contractors all at once. While balancing these considerations we believe in all cases something is thousands of times better than nothing. Many houses have minimal earthquake resistance and a little work can increase their chances of survival by a factor of 10. Other houses require so much work we tell our customers to forget about it and buy earthquake insurance.
If you phase the work it is important to be aware earthquake retrofits have components that all work together. For example, a shear wall with plywood alone is still very weak, bolts and shear transfer ties alone don’t do anything. So be sure that whatever you install includes all the necessary components. One complete four-foot-long shear wall with the bolts, plywood, and shear transfer ties does more than bolts all around the perimeter.
What if my old house is already bolted? Do I need to add even more bolts?
The building code completely dropped the ball regarding hillside homes and has a very serious code deficiency regarding houses built on flat lots. The Northridge earthquake also revealed deficiencies in the building code for soft story homes with living areas above the garage, which caused changes in the building code in 2000 to address this deficiency.
Is there any proof my retrofit will work? This retrofit is costing a lot of money.
We only use hardware and techniques that have been tested in hardware and shear wall testing laboratories. If a technique or hardware hasn’t been tested or is not based on sound science, we don’t use it.
There was also a test in an actual earthquake in the 1989 Loma Prieta Earthquake. An architect had a pair of identical Victorian houses in Santa Cruz with cripple walls. He retrofitted one but before he could retrofit the other one the 1989 Loma Prieta earthquake struck. One house fell off its foundation and needed $250,00 of work The retrofitted one needed plaster cracks repaired for $5,000.
Should I get a building permit?
A contractor is supposed to get a permit for “alteration or repair” of an existing house so we are supposed to get a permit. The other question is “Will a permit do me any good?” The answer to that is no, because a contractor can literally do anything they want and the building department will approve it. Bay Area Retrofit has been lobbying to change the law so that you actually get something after the city collects your seismic retrofit permit fees.
What about my old cracked foundation?
Contrary to intuition, cracks and foundation condition as a rule have very little impact on the ability for a house to be seismically upgraded. Steel reinforcing, also known as rebar, is used to prevent foundation cracking and was not required in residential foundations until July 1, 1997. Tests on old foundations have also shown old concrete in poor condition has no impact on a retrofit’s ability to perform. We have researched the subject extensively because after the retrofit, earthquake forces all end up in the foundation. We put this video and webpage on old foundations together to help you fully understand how old foundations work.
How long do earthquake retrofits usually take?
It really depends on the type of retrofit. If you don’t have cripple walls, then we should be done in one day. If you have a standard cripple wall retrofit we normally do all the bolting the first day, framing and shear transfer tie installation the next day, and plywood on the third day. If we need to work in living area where a lot of plaster or sheet rock must be removed you can probably expect 5 days. Soft story retrofits usually take 5 work days with lots of days in between while we wait for building inspectors, order custom steel the size of which we will only know once we get started, and of course all the digging and concrete work. Hillside homes can take a few days to a few weeks. If you have us take a look we will be able to give you a better idea at that time.
Is this work disruptive?
Some people wonder if they can still live in the house while it is being bolted and braced. All of the work takes place in the crawl space and though it is loud it is not deafening and you will be able to continue with your life. Phone calls will not be overwhelmed with noise and dust will not seep into the house. We only work during work hours and do all the bolting on the first day because that is what makes most of the noise. If your retrofit is in a room that has plaster or sheet rock on the walls you won’t be able to live in that room for a few days because we need to remove it in order to access the foundation. Our priority is to do that part of the retrofit as quickly as possible so you can get on with your life.
What can I expect from Bay Area Retrofit?
We mean it when we tell you that we take very seriously the trust you put in us concerning your home and safety. Perhaps knowing the Association of Bay Area Governments, the NewsHour with Jim Lehrer, and PBS Channel 9 , and the publisher of this article on retrofitting believe we can be trusted will help you decide. You are one of our neighbors and you are asking us to protect you. We will do all we can to make sure the money you pay us is used well and hope after the earthquake your home can be a shelter for your neighbors and friends. That is why we pay our crew by the hour and we tell them to take as much time as they need to be sure and do it right. That is why we spend so much time training our employees.
How can Bay Area Retrofit save me Money?
We think your own research will prove that we are the best informed and most experienced retrofit contractor in the Bay Area. This enables us to pinpoint exactly what your house needs so that we can provide the best protection for the least cost. We use information gleaned from previous building codes , damage records from previous earthquakes, and data from testing laboratories. We are the only ones in the State of California that uses the Flush Cut Method and a type of nailing which enables us to build earthquake resisting shear walls that are up to 58% stronger than our competitor’s.
What happens after I ask for an appointment?
We will set up an appointment with you and one of the owners, Jeff or Howard, will come over to take a look. They will look at your house very carefully to see if it has any serious structural weakness that could cause problems in an earthquake. A formal proposal is then drafted and sent to you. The entire process can take up to ten business days, though we do our best to get it to you sooner.
What areas in the Bay Area do you serve?
We primarily do cripple wall seismic upgrades in Berkeley and Oakland. We do a lot of soft story retrofits in San Francisco. Lately, we have spread out into San Jose and Fremont where our main focus is on bolted houses without cripple walls.