On October 17, 1989 the Loma Prieta Earthquake damaged, severely damaged and, in some cases, destroyed structures in several California Counties. A significant number of these structures were housing units, including manufactured homes (mobilehomes).
The Department of Housing and Community Development (HCD) has primary responsibility for manufactured housing in California and, unless assumed by local government, primary responsibility for enforcement of the California Mobilehome Parks Act. HCD's Division of Codes and Standards responded immediately following the earthquake to assist local governments with damaged manufactured homes and to assist the general public where HCD had primary enforcement responsibility within mobilehome parks.
Nine (9) California counties were designated as disaster areas following the earthquake. However, only three (3) counties had significant damage to manufactured homes. These counties were San Benito. Santa Clara and Santa Cruz. This report deals primarily with these three (3) counties since these are the counties where HCD efforts were focused and statistics gathered.
In several previous earthquakes HCD inspection personnel had reported differences in the performance of different types of manufactured home support systems. Though no statistical data was gathered and the damage to manufactured homes was not sufficient for a meaningful survey and analysis, there were growing concerns from inspection staff that manufactured home installation requirements needed to be reevaluated.
In addition to HCD inspection staff observations in previous earthquake responses, HCD had implemented California Health and Safety Code (HSC) Section 18613.5 providing for HCD certification of Earthquake Resistant Bracing Systems. While HCD had implemented this provision of law and notified manufactured home owners of the availability of HCD certified systems, their design and expected performance were largely based on engineering theory since none had been full-scale tested. For years prior to HCD implementation of the certification process in 1985 there had been numerous sales of non-HCD certified devices and installation of home-made devices as well.
The Loma Prieta earthquake and the resulting wide-spread damage to manufactured housing provided an opportunity to gather statistical data that HCD blended into our emergency response. Each HCD inspector, while carrying out their basic mission of emergency response, completed a short questionnaire on the manufactured homes observed. The questionnaire was simple so as not to impede the inspector's basic mission and was designed solely as a basis for evaluating manufactured home support systems.
