On the basis of 40 years of tornado history and more than 100 years of hurricane history, the United States has been divided into four zones that geographically reflect the number and strength of extreme windstorms. Figure I.2 shows these four zones. Zone IV has experienced the most and the strongest tornado activity. Zone III has experienced significant tornado activity and includes coastal areas that are susceptible to hurricanes.
To learn more about the wind history for the area where you live, check with your local building official, meteorologist, emergency management official, or television weather reporter.
Your house is probably built in accordance with local building codes that consider the effects of minimum, “code-approved” design winds in your area. Building codes require that buildings be able to withstand a “design” wind event. A tornado or extreme hurricane can cause winds much greater than those on which local code requirements are based. Having a house built to “code” does not mean that your house can withstand wind from any event, no matter how extreme. The shelter designs in this booklet provide a place to seek safe shelter during these extreme wind events.
The worksheet on pages 7 and 8 will help you determine your level of risk from these extreme events and will assist you in your consideration of a shelter. If you decide that you need a shelter, Section II will help you and your builder/contractor plan your shelter.