Earthquake Risk and Retrofit Effectiveness
- My house survived the 1989 Loma Prieta earthquake. I don’t need a retrofit.
- How large an earthquake will my retrofitted home survive?
- How do I know if I need to bolt my house to the foundation?
- What if my old house is already bolted?
- What about my old cracked foundation?
- Is there any proof my retrofit will work? This retrofit is costing a lot of money.
- Insurance vs. Retrofitting
- Why should I trust Bay Area Retrofit?
The Earthquake Retrofitting Process
Other Retrofit Questions
Questions with Answers
My house survived the 1989 Loma Prieta earthquake. I don’t need a retrofit. ^
Loma Prieta was 60 miles from the East Bay and was not the “Big One” even though it registered magnitude 6.9 on the San Andreas Fault, which runs along the coast. When the real Big One hits on the San Andreas Fault, you need to be ready for your Peninsula home to shake several times more intensely that it did on that day. And then there’s the inland Hayward fault, running through Milpitas up to Richmond, which links with minor faults in the south and north bay, and is overdue for a Big One of its own.
If a magnitude 7.0 earthquake hits on the Hayward Fault, cities like Berkeley and Oakland can expect very intense shaking because these cities straddle the fault line. These cities contain many older homes with serious structural weaknesses, so are likely to incur considerable damage. There may even be faults in the area that we aren’t currently aware of, similar to the Northridge Fault which was unknown until it caused the catastrophic Los Angeles quake in 1994.
How large an earthquake will my retrofitted home survive? ^
Geologists tell us that a good retrofit should resist a 7.3 Richter scale magnitude earthquake. We do our best to make sure your retrofit meets the design requirements of the California Existing Building Code. However, if your home has an exceptional vulnerability, such as being on a steep hillside, this may not apply.
How do I know if I need to bolt my house to the foundation? ^
The age of the house and the construction style are the most important factors. Homes built before 1958 are rarely bolted to their foundations. Foundation bolting isn’t the only factor in strengthening your home. You will need an evaluation by someone who understands how various homes have performed in previous earthquakes.
Braced and bolted homes remain on their foundations and sustain minimal damage.
What if my old house is already bolted? ^
San Jose has required foundation bolting since 1927. Fremont has required bolting since 1956. All cities in the Bay Area have required it since 1958. The size and spacing requirements for the bolts haven’t changed much. But it’s not the bolts that are a problem, it’s the fact that they have over-sized holes. Bolted houses with over-sized holes can still be very vulnerable to earthquake damage. These houses will without a doubt need shear transfer ties, as well as addressing the over-sized holes.
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. We use steel reinforcing, also known as rebar, to prevent foundation cracking. This wasn’t required in residential foundations until July 1, 1999. 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.
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 isn’t based on sound science, we don’t use it. Visit this page for details about how a retrofit strengthens your home – and what happens without one.
There was also an accidental 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 $250,000 of work. The retrofitted one needed plaster cracks repaired for $5,000.
Why should I trust Bay Area Retrofit? ^
We are the best informed and most experienced retrofit contractor in the Bay Area. You are our neighbors and you are asking us to protect you. We take this responsibility very seriously. We spend a lot of time training our employees carefully. Our goal is to use the money you pay us effectively, even if we lose money on it. We tell our crew to take as much time as they need to be sure and do it right. That is why we pay them by the hour rather than by the job.
What happens after I ask for an appointment? ^
An on-staff expert will inspect your home very carefully for serious structural weakness that could cause problems in an earthquake. We will then draft a formal proposal and send it to you for your approval. The entire process takes 6-12 business days, depending on the complexity of your needs.
This video shows you what one of our proposals looks like and how to read it.
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 essential 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 you use an engineer, you will need to pay them 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. Most engineers have very little residential retrofit design 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.
Should I get a building permit? ^
The question is will a permit do me any good? The answer to that is no, because a contractor can literally do anything they want. Building departments will approve anything contractors do, because there are no retrofit standards. Bay Area Retrofit has been active on a committee to create a workable standard. We want to change the law so that you get something for your building permit fees.
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. When we remove a lot of plaster or sheet rock in a living area, you can probably expect 5 days. Soft story retrofits usually take 5 workdays 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.
Who will do the work ^
Bay Area Retrofit employees performed all work. Our employees have years of experience. In addition, our expert CEO continuously trains them on new industry developments. We do not use subcontractors.
Is this work disruptive? ^
Some people wonder if they can still live in the house while we brace and bolt it. All of the work takes place in the crawl space and though it is loud it isn’t 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.
How can Bay Area Retrofit save me money? ^
History has shown when houses incur severe earthquake damage, it costs a fortune to repair them. Contractors charge triple or quadruple their normal rate due to high demand. And repair expenses are just the beginning. You will probably need to leave the state because all the temporary housing is occupied by other earthquake refugees, You may lose your job. Your kids must leave school, and the list goes on and on. It’s a lot cheaper to prevent this rather than dealing with it after it happens by installing an effective retrofit.
Will seismic strengthening increase the value of my home? ^
About one-third of the retrofits we perform are for newly purchased homes. This strongly suggests that many buyers prefer a retrofitted home. Retrofitting does not change the value of your home for tax assessment purposes.
