Seismic retrofit is a highly specialized field. Approximately 70% of the retrofits we do involve repairs or redo´s of jobs done by well-meaning contractors who did not understand the complex engineering principles involved in wood-frame retrofitting. (See False Security) On Howard Cook's prompting, the Contra Costa Times published an investigative article where they found 69% of all existing retrofits will fail in a major earthquake. This was based on a sampling of only 36 retrofits.

We have looked at over 1,200 previously retrofitted homes and, unlike the investigators for the Contra Costa Times; we have also looked behind plywood panels and have seen serious defects that are not otherwise visible. According to our much more thorough investigations, we believe the percentage of flawed retrofits is closer to 95%.

We do not want your home to receive one of those flawed retrofits so here are four questions you can ask a contractor to help determine if he is qualified to retrofit your home. If he cannot answer these quesions correctly, DO NOT HIRE HIM.

1. Does the contractor have a wood frame structural engineer he consults? If so, call that engineer and ask if he or she can verify that the contractor understands wood frame retrofit engineering principles. If the contractor cannot produce a competent wood frame engineer who can attest to the contractor's knowledge, do not hire him. You should also check the qualifications of the engineer by asking how many wood frame seismic retrofits he or she does each year. If the engineer has minimal experience in wood frame retrofitting, look for both another contractor and another engineer.

2. Why does the most recent building code require large square plate washers be used on foundation bolts rather than the small round washers allowed by previous codes and when did this code change take place?

Answer: During the Northridge earthquake, many mudsills were damaged when they split lengthwise at bolt locations.  Engineers discovered that bolts actually bent slightly and cut into the mudsill like an ax, causing the mudsill to split. Large square plate washers prevent this and significantly increase the strength of the bolt-to-wood connection. This code change was instituted with the 1997 Uniform Building Code, which was adopted statewide in July of 2000.

3. There are four seismic retrofit guidelines; can your contractor (and engineer) name at least two of them?

Answer:   1. Chapter A3 of the International Existing Building Code.
               2. The City of Los Angeles Retrofit Guidelines.
               3. The City of Seattle Retrofit Guidelines.
               4. Plan Set A Guidelines for the San Francisco Bay Area.

4. A contractor or engineer must determine the earthquake-resisting value of existing material on a house such as horizontal siding, old foundations, plaster, etc.  Where can this information be found?  

Answer: Table A-1-D in the International Existing Building Code

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