Is there anything a homeowner can do to reduce the chance that a great quake will level the homestead? A little, said Robert Holmes, a general contractor with Builtright Building Inspection, a Los Angeles firm that specializes in advising homeowners on how to protect their property. However, homeowners should also be warned that some efforts to strengthen their structures may backfire.
Homes built before 1935 were not required to meet some of the standards set after the 1933 earthquake and may have inadequate foundations. After 1935, buildings were required to meet much tougher standards and there is little that the average homeowner can do to improve them, he said.
Before making significant changes, Holmes strongly recommends that homeowners have an expert look at the property. Times Science Writer Lee Dye interviewed Holmes about the measures homeowners might be able to take.
Question: Have we learned anything from earthquakes?
Answer: There are many changes in building standards that grew out of the lessons learned in the 1933 earthquake in Long Beach.
For the Record
Los Angeles Times Tuesday November 7, 1989 Home Edition Part A Page 3 Column 3 Metro Desk 1 inches; 29 words Type of Material: Correction
Earthquake Section--In Sunday's special section, "Waiting for the Quake," the company employing general contractor Robert Holmes' was incorrectly identified. It is Boatwright Building Inspection.
Q: What changed?
A: A new law passed in 1935 called for reinforcing (steel) to be placed within concrete, and it called for a better mix of concrete which could stand a higher burst test. Prior to that, concrete might only withstand a burst test of 1,300 pounds or less. Concrete for residential construction is now set at 2,000 pounds and can be mixed to a higher burst strength if needed.
Q: What do you mean by burst strength?
A: It means the concrete will withstand specific pressure of 2,000 pounds per square inch before it crumbles.
Q: Does that mean that if your house was built prior to 1935, you need to suspect the quality of your foundation?
A: I don't know if I would use a word as strong as suspect, but it would be prudent to be more concerned about the foundation . . . and consider having it inspected.
Q: Is there something the homeowner can do to decide whether it is necessary to call in an expert? If you can drive a nail in it, would that tell you something?
A: Actually, that is something you can try. I have seen concrete that was degraded enough that you could push a screwdriver into it. Older, lower-grade concrete will often begin to flake and degrade. You will see it along the interior rim of a foundation and it will almost look like a pile of very fine sand that is from the foundation. If there are large cracks within the continuous footing, particularly if there is any vertical or lateral displacement of the foundation where cracking has occurred, that is a very good sign of distress.
Q: If the homeowner can drive a nail into the foundation, would that tell him he better get the experts in?
A: It would be prudent. And if a person were to find a very soft and crumbling foundation, it would be prudent to have it examined.
Q: So the experts come and say you have a really bad foundation. What can be done short of tearing the house down?
A: A foundation can be completely replaced without tearing down a house.
Q: How do you do that?
A: It's similar to when a building is moved. The house would be supported temporarily on a framework of girders and raised off its foundation. Then the foundation can be jackhammered out, a new footing and stemwall system installed, and the house lowered back onto the new foundation.
Q: But aren't we talking really big bucks?
A: It's significant. The number runs between $150 to $175 per lineal foot, so that can climb in a hurry. But short of wholesale replacement, it is also possible to augment an existing foundation. I have seen it with hollow masonry units which are put on top of an existing foundation and then filled with mortar to provide additional integrity.
Q: Prior to the early 1940s, the house was not required to be bolted to the foundation. Should a homeowner bore into the foundation and set some bolts in anchor cement to make sure it doesn't slide off?
A: Very often that is a good idea. But bolts can localize the force vectors. That means the energy transmission that occurs during an earthquake would be focused on the bolts and the trauma of an earthquake could tear the foundation apart.
Q: So you might shatter the foundation while trying to strengthen it?
A: Exactly. It would be a good idea to have an engineer check it first.
Q: If your home was built more recently, can you forget all this?
A: I would say so. There may be certain circumstances . . . a foundation can be undermined by erosion . . . but having a post-1935 house is about as good an assurance as you can get that you are going to have a good foundation.
Q: So generally speaking, if your house is built prior to 1935 you better take a hard look at the foundation and if it was built after 1935 there might be other things that would be more of a problem for you?
A: That is correct.
Q: You hear a lot of advice these days telling people to reinforce cripple walls . . . the short walls between the foundation and the main structure. Is that good advice?