Homeowners and contractors think a retrofit is the same as putting in bolts and nailing up plywood. Even engineers think it is a simple “paint by numbers” matter. It is not that simple.
This New York Times article, as well as this CBS News Report, are exposés on the commonly held belief that retrofits are simple. People have paid $10,000 or more for retrofits that will not work. This is a natural consequence of not having a retrofit building code .
The earthquake will let you know if you hired the wrong engineer or wrong contractor. Do some research. You should know as much, if not more, than the contractor you hire. Engineers might be able to do math, but even that has already been done for you. Do the same kind of research you would do if you were buying a new car. It is not that hard if you take the time.
Earthquake Retrofit Engineer and Contractor Screening
References from non-professionals won’t help you much. A contractor may have been easy to deal with and clean, but that is not important. You want to know if the retrofit will hold up in an earthquake, not how friendly the contractor was.
Asking an Engineer or Contractor the Right Questions
Asking questions about the subject is probably your best test of competency. Ask the contractor two or three of these questions and see if they know the answer.
Are they aware that putting brackets on posts is a waste of money and not recommended by any of the retrofit guidelines listed below?
1). Ask your contractor if they are familiar with all the extant retrofit guidelines.
- They should be familiar with the Bay Area’s Regional “Standard Plan A”
- And have studied “Appendix Chapter A3” of the 2016 International Existing Building Code
- Ask if the contractor knows about Seattle’s “Project Impact Retrofit Guidelines”
- Los Angeles Department of Building and Safety Standard Plan Number 1
- A guideline published by the Federal Emergency Management Agency after the Napa earthquake, “Earthquake Strengthening of Cripple Walls in Wood Frame Dwellings”
- And the most recent FEMA: Vulnerability – Based Seismic Assessment and Retrofit of One and Two-Family Dwellings
- Ask if he knows that the shear wall tables are in the Special Design Provisions for Wind and Seismic
Professionals such as members of the American Society of Home Inspectors are a good source for referrals. They see retrofits everyday and will know which contractor does quality work.
Contractors and engineers won’t be able to retrofit your house without being familiar with the science. This includes metallurgy and tests done in university and government testing laboratories, to mention tests done by hardware manufacturers. Familiarity with old building codes is a must.
One must also know how houses fail in earthquakes. Photos can be found at the Earthquake Engineering Research Institute. If you don’t know how houses are damaged, there is no way to know how to prevent that damage.
- Is your seismic retrofit contractor familiar with the resource manual Special Design Provisions for Wind and Seismic? This is the virtual Bible of seismic retrofit design, and anyone involved in this field should be familiar with it.
- Does your earthquake retrofit contractor know about the 4 methods used in building retrofit shear walls? These are the “Nailed Blocking Method,” the “Stapled Blocking Method,” the “Reverse Blocking Method,” and the “Flush Cut Method.”
- Does your seismic retrofit contractor know which organization is responsible for shear wall tests in Canada and the United States? This is very important, because their tests and reports are the basis of many provisions in the building code. The organization is called the The APA (American Plywood Association) Engineered Wood Association.. Is the contractor aware of tests regarding the performance of old foundations?
These tests were done by the Structural Engineers Association of Southern California in 1992, and showed low quality foundations without steel reinforcing perform quite well in earthquakes.
4). Is your contractor familiar with old building code provisions that specify the strength of existing structures? If you don’t know how resistant a building already is, you can’t know where to address the weaknesses. These code provisions are found in Table A4-A of the International Existing Building Code.
5). Does your seismic retrofit contractor where to find the shear wall strength tables? They used to be in the California Building Code. Now they are in the Special Design Provisions for Wind and Seismic.
6). Can they tell you what the principle of rotation is?
As you study you might find some questions of your own.