Wind Speed Zones and Seismic Design Categories

In compliance with Section 6-9-105(C) of the South Carolina Code of Laws, the Building Codes Council has defined the physical boundaries (streets, highways, streams, rivers and lakes) associated with the corresponding maps published in the International Building and Residential Codes, for the State of South Carolina. The wind speed maps in both documents are identical, and are applicable to all buildings and structures. The seismic design categories, however, are based on the International Residential Code and apply only to single and two family residences. Seismic design for all other buildings and structures must be based on the latest version of the Compact Disk titled “Seismic Design Parameters” (USGA Open-File Report 01-437), prepared in conjunction with the U.S. Geological Survey Building Seismic Safety Council, and Federal Emergency Management Agency, E.V. Leyendecker, A.D. Frankel, and K.S. Rukstales. To obtain a copy of the Seismic Design Parameters CD, contact the International Code Council.

How to View And Navigate The Maps

To determine basic wind or seismic information for a county, locate the name of the county on the following chart. From that point you can determine the county’s wind speed or speeds in miles per hour; the county’s seismic design category or categories; and if a map is provided, the direction the map must be rotated for appropriate viewing.

For counties having only one wind speed zone and one seismic design category, the information is stated on the chart only. A map of that county is not provided. For counties that have multiple wind speed zones or multiple seismic design categories, maps illustrating the physical location of the boundaries are provided.

Before opening a map, look at the “Map Rotation” column on the chart for the corresponding county. If the column states “No Rotation” the map will open in its upright position. If the column states “Clockwise” or “Counterclockwise,” the map must be rotated for proper viewing.

To open a map; click on the county icon. The maps are very memory intensive and may take several minutes to open or refresh on old or slow computers.

To rotate a map; from the Adobe screen, go to the “Menu Bar” and click on “View” then click on “Rotate Clockwise” or “Rotate Counterclockwise” accordingly. To shorten the opening time, a map may be rotated during the opening process.

To enlarge an area of a map; look at the “Magnifying Glass” icon (Zoom In / Zoom Out Tool) on the “Tool Bar.” If the magnifying glass has a plus sign in the center of the glass, it is in the enlarge mode. If the magnifying glass has a minus sign in the center of the glass, it is in the reduce mode. Select the enlarge mode and click on the “Magnifying glass” icon. A magnifying glass will appear on the screen. Move the magnifying glass to the area you want to enlarge. Each time you click the left mouse button, the area will enlarge at preset increments.

To enlarge an area in a quicker, more precise manner, move the magnifying glass slightly outside the area you want to enlarge. Click and hold the left mouse button. Create a box around the area you want to enlarge by moving the mouse. Release the mouse button.

To move a map in any direction; click on the “Hand” icon (Hand Tool) on the “Tool Bar.” A hand will appear on the screen. Click and hold the left mouse button and drag the map in the desired direction.