Q: What is an earthquake?
A: A natural shaking of the ground caused by sudden slippage on a fault line. Seismic waves spread outward from the fault rupture much like ripples do in a quiet pond when a stone is thrown into it.
Q: Earthquake prediction: Is one imminent?
A: The Federal Emergency Management Agency (FEMA) reports that scientists unanimously agree on the inevitability of major earthquakes in California. We may never see any degree of pinpoint accuracy. We are told by Caltech scientists that studies now indicate strong evidence of a 7+ quake occurring in California within the next two decades. But you can be sure that the further we get from the last earthquake, the closer we are getting to "the promised big one".
Here in California, there are more than 10,000 earthquakes in an average year, not including aftershocks. About 100 earthquakes larger than 3.0 occur each year.
Geologists can demonstrate that at least eight major earthquakes have occurred in the past 1,200 years with an average time spacing of 140 years, plus or minus 30 years. The last such event occurred in our area in 1857.
Q: My home has been here for more than seventy years; it has been through all of the past big ones. Why should I bolt now?
A: This question, by far, is the most frequent. In the 1991 Sierra Madre 5.8 quake, this logic fooled the owners of over 500 previously undamaged chimneys and moved a number of unbolted homes off foundations. More to the point: Since your home was built, there has not been a quake in our area nearly as strong as the 1989 Bay Area 7.1 quake. Experts tell us that if that quake occurred on the Sierra Madre or Elysian faults, the damages may easily have been one hundred fold!
Q: I have heard that bolting can actually cause greater damages. Who can I believe?
A: Experts in the physical sciences tell us that a properly anchored floor diaphragm uniformly distributes load and actually strengthens the components, while keeping your home securely in place.
Q: What are cripple walls? Why are they so dangerous?
A: A cripple wall is a short stud wall that extends from the top of the perimeter foundation upward to carry the floor joists. The danger comes from the fact that these inadequately braced components are in the seismic load path and can collapse like dominos in a large earthquake. Take care not to be duped. Not all homes have cripple walls!
Q: I understand you can make my home safer in earthquakes no matter what kind of foundation I have! What if my foundation is unreinforced brick?
A: Any foundation can be made safer. There are different solutions for different materials. A brick foundation can be retrofitted with embedded anchor bolts, and deteriorated mortar can then be flushed out and reconditioned with high density mortar.
Q: My arroyo stone foundation seems to be falling apart. Is it too late for me to think about reinforcement?
A: Not at all! In fact, we can restore your foundation to better than its original integrity. Then we can anchor the house to it using state-of-the-art materials and specialized seismically engineered procedures.
Q: A contractor friend says we don't need a permit or engineering for this kind of work. Is he right?
A: It is unlawful to perform this kind of work without a permit. Fines and penalties are heavy for violation. In addition you'll need both engineered details and a signed permit to satisfy disclosure laws when you sell, buy insurance or apply for a loan. Some cities are waiving permit and inspection fees to encourage homeowners to bolt to their foundations. If any contractor tells you that permits and engineering details are of unnecessary expenses, he is not acting responsibly.
Q: What is the cost of retrofit for a typical home?
A: Every home in this age bracket has unique differences with respect to height of the structure, profile, perimeter footprint, access to the work area, the materials and condition of the foundation, presence of cripple walls, and settlement problems.
These are just a few variables that will affect the final cost. For example, a two-story home requires 50% more anchor positions than a one-story structure. Our firm will at absolutely no cost or obligation provide you with a written seismic review and a contractual agreement for an exact cost of your individual pre-1938 home.
So you see there is no such thing as a typical home for us to describe here. But everyone seems to like ballpark figures; we find they can be misleading. However, in our recent experience we have completed several projects for as low as $1,700, many between $2,000 and $4,000, a few with major complications ran as high $10-12,000.
Q: How do retrofitting costs compare to entire foundation replacement?
A: You can figure from about $135 to more than $300 per linear foot perimeter. Total replacement is rarely our recommendation; however, the choice is yours and we are happy to furnish estimates.
Q: Will bolting really increase the value of my home on the open market?
A: Pretty simple. Just consider for yourself. Given a choice between two properties, the potential buyer will naturally choose the more secure home or expect to pay less for the seismically deficient home.
Q: Are insurance companies really refusing renewal for homeowner policies on unbolted homes?
A: That is exactly correct and lending institutions will soon follow. The reasoning is quite simple: Why make investment risks on items when the life expectancy is in jeopardy?
Q: What else should I do to preserve my fine home?
A: In a very basic sense, maintenance is preservation. Caring for all aspects of your building will help maintain its structural strength. Repointing mortar joints, replacing rotted wood members, and keeping wood and foundations dry will help preserve a building, even in an earthquake.
Water can create deterioration in many ways and locations. Keep your roof and eaves in good condition. Drain downspouts away from the foundation. Slope the surrounding ground away from the house. Minimize foundation plantings and irrigation. "Ponding" water can cause settlements that may weaken the building in many ways.