Tumbling Dice

But those were still Zone III units, not the Zone I units found in most of tornado country. Upgrading the whole country to the Zone III standard (which some have suggested) might cost his company $2,500 or $3,000 per unit for a typical double-wide, Kessler estimates: Roof trusses would have to be spaced at 16 inches on center, walls would need continuous structural sheathing, and many framing connections would have to be reinforced with steel connectors. For other companies, whose Zone I units may not be built as well as Palm Harbor's to begin with, the up-charge could be even greater. And that's not counting improved installation—the requirement for vertical straps to prevent overturning, with diagonal straps also installed at the same locations, which local inspectors would have to enforce. “I'm seeing a price of $75 to $150 per connector,” says Kessler.

Is it worth it? At a guess, the safety improvements might only raise the monthly housing cost for manufactured-home residents by $50 to $100 per month. And that cost might be offset in many cases by improved financing terms. But even so, given the relatively small and sporadic risk of an actual tornado strike, it remains debatable whether the cost of safety upgrades is worth the benefit. Even after last year's deadly strike in Eastbrook, Ind., Gov. Mitch Daniels remarked, “When you see the randomness of an event like this, you have to reckon with the fact that we cannot expunge every vestige of bad luck from life.” (Daniels did, however, support a move to require licensing of manufactured-home installers and also improve foundation tie-down connections.)

Mobile-home residents themselves may not choose safety over economy. For example, retired police officer Jerry West Sr. barely escaped a tornado that destroyed his mobile home in Madison County, Tenn., by crawling out the window into a makeshift shelter he had built himself. He then reportedly moved back into a new unit placed on the same site. He was considering upgrading his shelter, reported The Jackson Sun, but not moving to a more substantial building. The 63-year-old West told the paper, “I don't think a mobile home is near as safe as a house on a permanent foundation. But I guess that's the way I choose to live.”

And even an expert who is fully aware of the risks and the structural issues, such as engineer Reinhold, is hard pressed to put tornado shelters at the top of his list of priorities—even after a Clemson University colleague experienced a near-miss from a strong tornado that could have killed the man's whole family. Rein-hold lives in a conventional site-built house, not a HUD-Code home, but he has considered an in-house tornado shelter. Says Reinhold, “If you look at the statistics—really deal with the risks—and you are going to spend $4,000 on a tornado shelter, well, you know—I've got teenage kids. I looked at that choice and I said, ‘I'm going to put that money into the safest automobile that I can afford for them to drive,' because that is the greatest risk.”

Texas Tech engineer Tanner acknowledges the cost issue: “You're living in a mobile home because you do have limited means, and so every nickel is important to you.” But Tanner's not ready to give up on improving the industry's safety performance. “America has been built on doing things better and smarter,” he argues, “and I think we can do that in the manufactured-housing industry—and without taking a significant quantity of people out of owning their home.”

Weather scientists grade tornadoes on the Fujita Scale (or F Scale), named for the late tornado expert Theodore “Ted” Fujita. Tornado winds are hard to measure directly. When they do happen to strike a weather station, they break the wind gauges. So instead, the Fujita Scale rates tornadoes from F0 to F5 based on destruction of natural and man-made objects. “In its rawest form, the Fujita Scale is not a wind-speed scale; it's a damage scale,” explains engineer Tim Reinhold.

In an attempt at rough precision, the F Scale takes into account the difference between various construction types—and it assumes a variance between mobile-home and stick-house survivability. Signposts for an F1 or “moderate” tornado, toward the bottom of the scale, include the criteria “peels surface off roofs; mobile homes pushed off foundations or overturned.” An F2 or “significant” tornado, according to the scale, would cause “roofs torn off frame houses; mobile homes demolished.” Not until F4 does the scale expect “well-constructed houses leveled.”

A new “Enhanced Fujita Scale,” developed at Texas Tech, lowers the wind-speed estimates associated with various degrees of damage, but provides a spread of possible wind speeds for particular damage indicators. By the enhanced scale, a stick-built house showing “total destruction of the entire building” would indicate winds of about 170 mph (within a broad range from 142 to 198 mph). Manufactured housing, by contrast, would experience “destruction of roof and walls, leaving floor and undercarriage in place” around 105 mph. “Unit rolls or vaults; roof and walls separate from floor and undercarriage” around 109 mph. “Undercarriage separates from unit; rolls, tumbles, and is badly bent” around 118 mph. And “complete destruction of unit; debris blown away” occurs at 127 mph (the range is 110 to 148 mph). In other words, the new scale, which is based on both field observation and engineering analysis, assumes that weak tornadoes, peripheral winds from stronger storms, or even straight-line winds from ordinary thunderstorms—winds which might do only non-structural damage to well-constructed stick homes—are likely to cause major structural damage to many mobile homes.