Questions and Answers
What could happen to an unbolted home in the next strong earthquake?
The house could slide off its foundation and possibly collapse. more »
Earthquakes are rated by strength on a scale from 1 to 10 During a 6.3 quake an unprotected house could slide 2" to 3" breaking sewer drain lines, water supply lines, and unprotected glass. In a 6.5 quake the house could slide 4" to 6" causing gas leaks and some structural damaging. A 6.8 could cause the house to slide 8" to 12", causing possible partial collapsing of structure, electrical shorting. At 7.1+ the house could be a total loss and a fire hazards. Most, if not all of these problems can be minimized or avoided entirely with a properly planned and executed bolting.
What is the cost of a seismic retrofit for a typical home?
As low as $4,200, many between $4,200 and $6,000. more »
Every home in the "needs seismic retrofit" 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/pony 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. A home with stepped foundations requires a minimum of two anchors per step, and so on.
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 them very often misleading. However, in our recent experience we have completed a few projects for as low as $4,200, many between $4,200 and $6,000, a few with major complications ran as high as $10,000-12,000.
Will bolting really increase the value of my home on the open market?
Given a choice between two properties, a potential buyer will naturally choose the more secure home, or expect to pay less for the seismically deficient home.
My home was built after 1980 do I need a seismic inspection
Many homes built after 1980 will not withstand an earthquake which a properly secured home will. Inspections of post 1980 constructed homes which failed in earthquakes in the San Francisco Bay area showed that the bolting method was incorrect and the major reason why the homes fell off their foundations.
My house has survived for 70 years. Why should I get house bolting now?
Since your home was built there has not been a strong quake in our area. You should retrofit your home because it is a preventative measure to minimize the damage to your home and maximize the safety of your family in the event of an earthquake. more »
In the 1991, 5.8 Sierra Madre quake this misconception hurt the owners of over 500 previously undamaged chimneys and moved a number of homes without house bolting off their foundations. Since your home was built, there has not been a strong quake in our area. A retrofit is simply a preventative measure to minimize the damage to your home and maximize the safety of your family in the event of an earthquake. Experts tell us that if that quake occurred on the fault lines in Coastal British Columbia the damages may easily be one hundred fold!
I have heard that bolting can actually cause greater damage. What can I believe?
This is a misconception. Not bolting your house is like saying, "I don't have brakes on my car because, if you put them on too hard, you could bump your head". more »
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. Some people have told me, "I have heard it is better to leave a foundation unbolted: that way in small earthquakes the house can slip around a little and dissipate the energy without causing any damage." The truth is that the bolts never come into action until the house starts to move. The amount of unbolted elasticity sacrificed in small quakes results in a quantum benefit in larger quakes. Not bolting your house is like saying, "I don't have brakes on my car because, if you put them on too hard, you could bump your head".
What are cripple walls/pony walls? Why are they so dangerous?
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 these components are in the seismic load path and are often inadequately braced. They can collapse like dominos in a large earthquake.
I have a brick chimney on my house does this needed to be protected for earthquakes?
All brickwork and masonry is rigid and in an earthquake is highly prone to cracking and falling. Chimneys and other masonry should be inspected to ensure that it is in proper condition and properly secured to prevent failure in an earthquake.
Can any type of foundation be reinforced?
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.
What else should I do to preserve my home?
In a very basic sense maintenance is preservation. Caring for all aspects of your building will help maintain its structural strength. Repointing (fixing) mortar joints, replacing rotted wood members, and making sure water runs away from the foundation will help preserve a building, even in an earthquake.
Are earthquakes truly inevitable?
Yes. more »
The Federal Emergency Management Agency (FEMA) and Canadian Geographic Service reports that scientists unanimously agree on the inevitability of major earthquakes in California, Oregon, Washington State, British Columbia and Alaska We may never see any degree of pin point accuracy. We are told by scientists that studies now indicate strong evidence of a 7+ Richter Scale quake occurring within the next two decades. It could be tomorrow! Make no mistake - you can be sure that the further we get from the last earthquake the closer we are getting to "the big one".
What causes an earthquake?
An earthquake is a natural shaking of the ground, caused by the sudden slipping of rock on a fault-line. A fault line is the point where tectonic plates meet. Seismic waves spread outward from the fault rupture much like ripples do in a quiet pond when a stone is thrown into it. Sometimes the plates only jump a tiny bit causing windows to rattle. Other times the displacement is so violent that it sends seismic waves booming out in all directions with forces similar many atomic bombs. The result is called an earthquake.
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