Seismic safety concerns and structural renovation and repair can be a dizzying subject! As a homeowner, the best thing you can do first is become informed about the issues involved, the potential problems, and the available solutions.
Our Bay Area Retrofit FAQ is our attempt to shine some light on a few of these areas where we have noticed our customers need some more information. If you have a suggestion for a topic you would like to see covered in our FAQs, please let us know.
Since 1978, Building Codes for new construction have required seismic strengthening. Homes built before 1978, however, were not built to withstand seismic activity. Therefore, it is crucial that any home built in California prior to 1978 be seismically upgraded.
We also recommend that homes built after 1978 be evaluated aswell. The state of the art continually changes as engineers and other experts learn fromstudying building performance after earthquakes. As a result of the 1989 Loma Prieta (magnitude 6.9) and the 1994 Northridge (magnitude 6.7) earthquakes, standards for retrofitting have improved. Therefore, even if a home was built after 1978, improved, supplemental retrofitting is available that will further strengthen the home.
The answer to this question depends on several factors. In acknowledgment of the major seismic risk facing homeowners in California, the state recently adopted an Earthquake Retroﬁtting Code as part of the 2007 and 2010 California Building Code. In “Appendix Chapter A3” of this Code, engineered, prescriptive seismic designs were approved. The most widley used prescriptive design is commonly referred to as “Plan Set A”. If your home meets the guidelines for using Plan Set A, it is not necessary to hire an engineer.
If the design and construction of the particular house does not fall within the Plan Set A guidelines, most Building Departments require an engineer designed plan to issue a permit for seismic retroﬁtting.
J. David Ford can determine if your house falls within the guidelines for the prescriptive designs or whether it is necessary to obtain an engineer design. We work with many local engineers and can coordinate the inspection, design and permit process.
There are 3 major parts of a typical seismic retroﬁt: The house must be bolted to the foundation to protect against lateral displacement of the mudsill from the foundation. The walls must be strengthened with plywood shear panel to prevent/minimize lateral movement during an earthquake. Depending on the particular structural design of the house, alternative methods such as Hardy Frames, Simpson StrongWalls, Moment Frames or custom fabricated, engineer designed methods can be used in lieu of shear panel. Seismic transfer hardware must also be installed to connect the shear paneled cripple wall (or shear panel alternative) to the ﬂoor diaphragm.
It is important that proper materials and installation methods be used. In an in- depth investigation of 35 retroﬁtted houses along the Hayward Fault, Contra Costa Times reporters found that in 24 of the 35 homes inspected, Owners had a false sense of security about earthquake protection because their retrofitting had been done improperly. The article concluded that:
“Installed properly, [retroﬁtting] can prevent walls from shifting and houses from sliding off their foundations and collapsing. [It] can save lives. Installed improperly, or only partially, [it] is little more than a collection of worthless materials that offer minimal to no earthquake protection.”
- Contra Costa Times, March 5, 2006, Jessica Guynn and Thomas Peele
The answer to this question depends largely upon the individual construction of the house. Most homes have a sub-area or crawl space. A majority of the work is done in this area and can be done without entering he house. Plywood shear panel can be installed in the sub-area, on the exterior or interior walls. Where the design requires removing exterior stucco or interior sheetrock to install shear walls, J. David Ford Construction will restore all of the ﬁnishes. As distinguished from many seismic contractors, J. David Ford has in-house ﬁnish carpenters. Through our longstanding network of painting, stucco, plumbing and electrical sub-contractors we are able to complete all of the related aspects of the work to the highest standards at competitive prices.