The most severe and least understood destructive forces imposed on houses are generated by tornadoes. Most of the funded research activity, however, has been directed to hurricane resistance, specifically along the East Coast of the U.S.
A psychological attitude seems to have developed that we should work to improve the design and construction of houses for small and intermediate wind forces and assume that little can be done about saving houses that will be ravaged by the more severe tornadoes and hurricanes. For communities already devastated by a major disaster, the attitude seems to be that it cannot happen here again. Or, a hope that the next bad one will happen in a rural area where not so many people will be killed and not so many houses will be converted to kindling.
The process of developing building codes in the U.S. is somewhat confusing, and perhaps haphazard, being one that involves government, private societies, lobbyists, individuals, and materials interests. The International Residential Code for One- and Two-Family Dwellings (IRC) applies to all matters related to designing and building houses. The IRC, however, is completely silent about provisions for tornado-resistance. It includes comprehensive provisions for hurricanes, termites, floods, earthquakes, decay, and storm shelters, but not one word about tornado protection. So, in effect, there is no tornado code protection for dwellings and their occupants in the IRC.
It is possible that code writers consider hurricane winds and tornadoes as one topic, when in reality, they are completely different, with maximum tornadoes being four times as destructive as a maximum hurricane. The IRC basic wind speed maps only require design for higher wind speeds along the Eastern and Gulf Coast of the U.S. The remainder of the country only requires design for 90 mile/hour winds.
The only houses in the world that have successfully survived big winds and big earthquakes are constructed with reinforced concrete using a box-frame structural concept that was developed 50 years ago and has been exposed to a number of severe wind and seismic events without structural damage. The entire outside of the house is built as a six-sided reinforced concrete box, like a ship.
The practice in North America that has us seriously concerned is that of building houses with concrete walls and then, after installing wood-framed roofs, implying tornado resistance. There is not one shred of evidence that a wood-framed roof system, even on reinforced concrete walls of some type, will survive an EF4 or EF5 tornado. For more information on this, go to http://www.tornadoproofhouses.com.
— Joe Warnes, CPM Associates, Roseville, Calif.