As of June 22, 2011, the National Weather Service (NWS) estimated that approximately 1,564 tornadoes had ravaged the country so far this year, causing about 536 fatalities. This compares with an annual average of 1,274 for the past decade.
Just when we thought the worst of the 2011 tornado season was over, Mother Nature had other ideas and unleashed powerful tornadoes (videoshows twister forming over the Connecticut River) on June 1 in a very unlikely location--western Massachusetts, where at least 3 died in and around Springfield. Although hardly unprecedented*, nevertheless the June 1st tornadoes were of unusual severity. And yesterday, a tornado touched down in the vicinity of Louisville, damaging barns at Churchill Downs.
With all of these reminders that tornadoes can occur almost anywhere, there’s been renewed interest in what we can do, if anything, to protect ourselves in our homes from these monster storms.
Retrofitting vs. new construction
Retrofitting an existing home with a reinforced “safe room” is a relatively low cost option, says Ernst Kiesling, executive director for the National Storm Shelter Association. It would cost about $2,000, he says, to harden and stiffen an existing bathroom or closet. Alternatively, it would cost somewhat more to build either a remote underground or partially underground shelter.
But even this relatively small expense might seem unnecessary to some, as statistics have shown that even in tornado-prone areas, the chances of a particular home being struck by a tornado during its rated life span of 50 years is only about 1%. (Surprisingly, the Texas Tech Wind Science and Engineering Research Center has grave misgivings about remote underground shelters because people tend to wait until the last possible minute before taking refuge, thereby subjecting themselves to flying debris, etc.)
The picture becomes a little murkier when dealing with new construction. According to Stan Peterson, of the American Institute of Architecture Disaster Assistance Task Force, [to tornado-proof a home] “you’re talking about very well designed connections all the way down, very well engineered and very well tied together.” Kiesling, of the Storm Shelter Association, adds that all of this “greatly increases the cost [to build] the house.”
The Texas Tech center says that to really “tornado-proof” a home, “the walls, roof, windows, doors and garage doors must be missile-resistant and the connections of the structural elements must be capable of withstanding 250 mph wind pressures.” (A 250 mph wind has 25 times the force of a 50 mph wind.) The garage door itself ideally should be made of extremely sturdy stock because “if your garage door fails,” says Larry Tanner, of Texas Tech, “you get a good deal of internal pressurization, which can blow out walls and ceilings.” Unfortunately, however, most of today’s garage doors seem to be of the weaker variety, at least in this reporter’s neighborhood.
What about yours? Do you think it can withstand the “big one?”
Are ICF’s the solution?
All in all, according to the above sources, it isn’t reasonable, practical, or prudent to tornado-proof a new home, at least using standard construction methods. On the other hand, the increasing use of “insulating concrete for ms,” or ICF’s (LEGO®-like systems composed of 5-inch thick styrofoam building blocks filled with 8 inches of concrete and steel reinforcements from floor to ceiling), hold great promise and have held up well in extreme situations, according to Pete rson of the Disaster Assistance Task Force. But at what cost? Neither Kiesling nor Peterson seems to say.
Others say that ICF homes can initially cost anywhere from the same (mostly those with a vested interest) to as much as 20% more (real-world ICF contractors) than wood-framed homes, depending on size, configuration, region, and other factors. There is general agreement, however, that payback can come within a few years time, due to significant energy, insurance, and other savings.
Another possibility: SIP’s
Structural insulating panels, or SIP’s (or foam core panels), are somewhat similar to and sometimes paired with ICF’s. Although around for some time, they are just now gaining more favor by builders and consumers due to their strength, “green” qualities, insect and mold resistance, and other attributes—much like the benefits of ICF’s. “The reason why it works better than two by fours or stick framing is because there are very few seams and gaps in the walls compared to stick framing,” says Michael Lamb, certified energy manager at the Energy Efficiency and Renewable Energy Clearinghouse, a division of the DOE.
Lamb goes on to explain that with conventional construction, air blows into wall cavities, but with SIP’s, there are fewer seams and leaks and more uniform wall insulation.
Most SIP systems consist of wall panels with a structural board “skin” and layers of polystyrene or polyurethane between them. But OceanSafe Building Systems, a firm currently helping to rebuild New Orleans’ 9th Ward to withstand 190 mph winds, uses a proprietary method, called SSIP’s (steel structural insulating panels). OceanSafe believes that its steel framing is stronger, more impervious to mold and insects than regular SIP’s, and only slightly more costly than conventional construction, a benefit confirmed by Lamb, of DOE.
A key consideration for those who might be interested in either an ICF or an SIP home: how will it fit into the community? It appears that, for the most part, this is not an issue, as both types of construction can be configured to conform well to various architectural styles.
So, for those truly concerned—both here and elsewhere--what’s the most practical course of action? Stan Peterson recommends following guidelines from the Federal Emergency Management Agency (FEMA), which call for building a “safe room” in the basement, on a concrete slab-on-grade foundation/garage floor, or an interior room on the first floor. Another alternative? Move to Alaska, Vermont, or Rhode Island, each of which averages less than one tornado per year.
Tornado damage scale trivia
The Enhanced Fujita Tornado Damage Scale (EF1-EF5), unveiled in 2007, replaced the old F-Scale created by Ted Fujita in 1971. According to the National Climatic Data Center (NCDC), the old scale actually went up to F12**, or Mach 1 (the speed of sound, which is 738 mph at -3°C)! What was Ted thinking! As the NCDC pointed out, however, since complete destruction, including the instrumentation, would have already occurred at the F5 level, all ratings beyond F5 are essentially meaningless.
*One of the worst northeast tornadoes on record was the F4/F5 (old scale) Worcester, MA tornado of June 1953, which killed 94 and occurred almost exactly 58 years ago on June 9th of that year.
**In actuality, the old scale was almost never displayed as an F0-F12 table.