Article By: Art Angelo, President
Sure Safe Industries International, LLC
Escondido, California
Ironically, one of California's most destructive earthquakes spawned the most effective technology for seismic home protection.
For decades, mobile homes and classrooms fared poorly in California's earthquakes -- but the Loma Prieta quakesignaled a major change. The 1989 temblor that killed scores in the Bay Area and left billions of dollars in property damage, also virtually destroyed one mobile home park in Hollister. Five mobile homes in that park emerged unscathed, while almost 100 units tilted, slid or were impaled on their own supports.
Those five surviving mobile homes had one thing in common, they were the only ones in the park equipped with a seismically engineered foundation technology for manufactured homes. Engineer Tom Naraghi and building executive Art Angelo had developed the system for the load-bearing demands of manufactured housing. They knew that stabilizing the steel-frame undercarriage of a mobile home required a fresh approach. Conventional poured concrete foundations had evolved to support site built homes, but adapting them to mobile structures proved difficult and costly.
Seismic Engineering for Mobile Homes
Naraghi and Angelo targeted the I-beams that provide principal support for manufactured housing. Their system attached directly to this steel-frame structure, which was anchored by ground-conforming poured concrete bases. This technique combined the strength, resilience and support mass required to protect mobile homes during earthquakes.
Hollister, one of the most earthquake-prone towns in California, offered an ideal test site for the prototype. The low-cost system proved highly effective in 1989 and went on to save many structures during the 1994 Northridge earthquake. These experiences demonstrated that manufactured housing placed on well engineered, permanent foundations could withstand seismic stresses as well as, or even better than, conventional site-built homes. A turning point was reached in the sad history of earthquake-damaged mobile homes.
Meanwhile, lawmakers nationwide began to realize that the structural failures of mobile homes, classrooms and other buildings stemmed from poor installation -- not from the quality of the structures themselves. The manufactured housing market had long suffered from a tragic mismatch between the quality of its homes and what passed for foundations. This problem had haunted the industry since the 1976 HUD code established nationwide standards for mobile homes but failed to specify how the homes were to be installed.
Toward a New HUD Code
Manufactured housing is engineered to withstand severe forces. The stress of driving a mobile home over miles of freeway is at least equivalent to a Richter 8 earthquake. But historically, dealers set homes on flimsy supports, typically posts and piers. Without real foundations, mobile homes were vulnerable to wind and seismic forces, ground settling and other conditions. Even without earthquakes, manufactured housing had long been infamous for cracking and tilting, as well as for floors that separate, windows that jam and other problems that mysteriously appear over time.
Then came the Manufactured Housing Improvement Act of 2000. This amounted to a "new HUD code" that mandated, among other things, tough standards for foundations. Lenders quickly responded by making conventional mortgages available to mobile home buyers, backed by the likes of FHA, Fannie Mae and Freddie Mac. By 2004, strict specifications for manufactured housing foundations will become the law of the land, in many cases superseding state and local regulations.
The new HUD code (HUD-007487) spells out what does and does not constitute a permanent foundation for a manufactured home. It acknowledges that mobile housing is built in a factory, transported to a site, then attached to a foundation -- which allows little margin for error. Adding a factory-built home to a site-built foundation involves tight tolerances. The foundation must be precisely measured and constructed.
The new HUD code validates the Naraghi/Angelo approach -- permanent foundations that can be cast in place, once the house is on site, and that engage the mobile home's steel undercarriage to evenly distribute the load. The structure and foundation integrate tightly, functioning as one structural unit. The per unit cost rarely exceeds $5000.
Across the nation, regulators continue to demand that manufactured buildings use permanent foundations. Californians saw a decade-long battle over mobile classrooms. In 2000, legislators required all mobile classrooms in California schools to meet requirements for seismically engineered foundations. This urgent statute went into effect immediately, with all California schools to be in compliance by late 2002.
Manufactured Housing's New Era
With the law on its side, manufactured housing, once a stepchild of the industry, is about to go mainstream. Today, perhaps 10 percent of homebuyers can take an initial leap into the market for $300,000-$400,000 housing. Manufactured homes on well engineered foundations change that equation. They reduce new housing costs from, say, $100 per square foot to something approaching $40 per square foot. With engineered, permanent foundations, manufactured homes and structures are finally on solid ground.
