Case for Enhanced In-Home Protection from Severe Winds

This paper presents the results of a study to investigate methods for providing low-cost protection from hazards associated with tornado strikes or other severe wind events. Included are discussions of physical wind damage, the tornado hazard in the United States, and the relative performance of various physical mitigation measures for existing houses (retrofit options). The results can, however, be extended to new construction, where the incremental costs are expected to be far lower than those associated with modifying existing structures. Three primary tornado hazards are discussed: wind pressures, windborne debris, and falling objects. One of the primary objectives of this study was to develop data on impact resistance of typical construction materials. Impact resistance was defined in terms of both first damage and through-penetration. The results suggest that the impact resistance of walls composed of layers of materials can be estimated by summing the impact resistance of the individual layers. The study also considered, on a limited basis, the threat of falling objects such as trees or large branches. Results suggest that a wall designed to resist debris impact will also exhibit satisfactory performance against tree-fall. This paper provides information that may be useful for people making decisions about whether (and how) to modify their homes to provide an increased level of protection from severe windstorms, but not necessarily at the level specified in the FEMA National Performance Criteria for Tornado Shelters and provided by the FEMA 320 designs.