8 tips on Finding a Good Residential Earthquake Retrofit Contractor
Many residential earthquake retrofit contractors in Oakland, Berkeley and San Francisco claim to be experts, but be sure s/he understands the science of residential seismic retrofitting. According to this New York Times article as well as this CBS News Report, many seismic retrofits of people’s homes are being done incorrectly. We don’t have such a code so make sure your contractor understands the science behind foundation bolting, cripple wall bracing, or other seismic upgrades.
The Science of Retrofitting
Residential seismic retrofitting requires a good understanding of metallurgy. It requires knowledge of the most up-to-date test results at the shear wall testing labs of the American Plywood Association and wood performance labs of the American Wood Council. Also very important is a thorough understanding of how houses fail in earthquakes, based on empirical evidence. A great source for this knowledge is the Karl V. Steinbrugge Collection of slides and photographs of earthquake-damaged homes. One should also be familiar with old building codes and have individual experience taking old buildings apart. Remarkably after 21 years of taking older homes apart, we have found the craftsmen in those days built far better homes than they do today. Unfortunately, they did not have earthquakes in mind.
The practical part of seismic retrofitting is the ability to apply this science in a practical way to the installation of bolts, plywood, shear transfer ties and other earthquake-resisting hardware. That is why it is so important that your contractor understand the science.
My Residential Earthquake Retrofit Contractor was Recommended by Friends and my Real Estate Agent
Asking for references from non-professionals won’t be much help because all they really prove is that the contractor was friendly and cleaned up after himself. It says nothing about how good a job he did. Unlike painting or tile where quality is obvious to the eye, you will only know if a seismic retrofit was done correctly when it is tested during an earthquake. Asking professionals such as the members of the American Society of Home Inspectors about the quality of a contractor’s work will give you much more valuable information. Remember, even giving thousands to an engineer may not assure you good quality seismic improvements.
Can your seismic retrofit contractor answer these questions?
1- Does your seismic retrofit contractor know what the Base Shear Formula is and how it would apply to your retrofit?
If you like reading more than watching a video, the same information can be found here.
This is important because it is essential to an effective design.
2- Has your seismic retrofit contractor read Thor Matteson’s book on shear walls?
This is the bible of shear wall construction. Any good retrofit contractor who keeps up on the latest research in seismic retrofit design and practice should be very familiar with it.
3- Does your earthquake retrofit contractor know about the three methods used in soft story retrofits?
This is an important reference because it proves he has experience with them all.
4- Does your seismic retrofit contractor know which organization is responsible for shear wall tests in Canada and the United States?
Answer: The American Plywood Association
This is also very important because their tests and reports are the basis of good shear wall designs that have been tested for their effectiveness.
5- Does your seismic retrofit contractor know which chapter in the 2013 California Existing Building Code applies to home retrofitting?
Answer: Appendix Chapter A3 of the International Existing Building Code.
Even though this document is dated, understanding the material therein is still important.
6- Is your contractor aware of any tests that have been done regarding the performance of old foundations and retrofit foundation bolts in regard to earthquake resistance?
This is critical so that your contractor knows when and when not to do very expensive foundation work.
7- Does your contractor know where the earthquake resistance of old building materials such as old siding, foundations, roofs, flooring, stucco, etc. can be found? If you don’t know how resistant a building already is, it is difficult to pinpoint exactly what it needs.
This is important because many existing connections are already earthquake resistant and there is no point wasting money addressing them.
8- Does he know which Chapter in the 2013 California Building Code contains the prescriptive seismic provisions for new homes?
Answer: Chapter 23.
This is important because much of this information is used in effective seismic retrofitting
9- Does your seismic retrofit contractor know where many of the code approved seismic provisions are found that cannot be found specifically in the 2013 California Building Code? This part of the code addresses things like the principle of rotation used in soft story retrofits
This is an important reference because it contains information on seismic retrofit design and lateral force resisting systems you will not find anywhere else.