From ASCE 7-05: "The area used to determine GCp. For component and cladding elements, the effective wind area in Figs. 6-11 through 6-17 and Fig. 6-19 is the span length multiplied by an effective width that need not be less than one-third the span length. For cladding fasteners, the effective wind area shall not be greater than the area that is tributary to an individual fastener."
Components and Cladding is generally used as stated for a component say a window.... the window would be designed by means of components and cladding utilizing the window size as the effective area. 4'x8'=32ft2
It may be better if you define the component you are designing and we can better help you determine the associated effective area.
The definition for "effective wind area" is found in Section 6.2. For a girt it is basically a minimum of the (span of girt) squared / 3. If the actual distance between girts is greater than span/3 then you can use span * spacing. Note, a continuous girt is figured the same as a simple span girt. You get no benefit for continuity.
