Monday, January 21, 2008
What's the Wind-Borne Debris Region?
Wind-borne debris regions are defined as areas along the Atlantic and Gulf Coasts where the design wind speed is 120 mph or above, or within one mile of the coastal mean high water line where the wind speed is 110 mph or above. In these regions, the standard requires the designer, either an engineer or an architect, to assume that the windows and doors will be broken by wind-borne debris unless those openings are protected against such items. Protection can be achieved through the use of hurricane shutters or impact-resistant glass.
The wind-borne debris region extends about five miles inland in most cases and considerably further in others. But, in the Panhandle region (sections of northern Florida from the Walkula/Franklin County line to the western edge of Escambia County), the legislature designated the wind-borne region as the land within one-mile of the Gulf Coast.
After Hurricane Andrew, in 1992, Miami-Dade County established the first requirements for wind-borne debris protection and developed test requirements that shutter and impact-resistant glazing systems must pass, under the code (Fla. Building Code § 1626). Since then, the American Society of Testing and Materials (ASTM) has developed testing standards. Products must pass one of these tests to be accepted for use where protection is required. The exception is plywood panels that conform to a set of prescribed specifications, according to Rick Dixon of the Florida Department of Community Affairs. Today, the Florida Building Code uses the America Society of Civil Engineers Standard (ASCE) Standard 7 as the basis for establishing wind-borne debris regions and wind-borne debris protection. The standard requires builders either to (1) construct buildings that can withstand the additional pressure that results when wind gets into a building through a hole in the wall or broken door or window and pressurizes it (like blowing air into a balloon) or (2) protect glazed openings in walls (e. g. , windows and glass doors) from debris borne by high winds (refer to Florida Building Code, Chapter 16).
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