Table 30.10-1 Steps to Determine C&C Wind Loads for Roof Overhangs Step 1: Determine risk category of building, see Table 1.5-1 Step 2: Determine the basic wind speed, V, for applicable risk category, see Figure 26.5-1A, B, or C Step 3: Determine wind load parameters. The external pressure coefficient for the covering on the underside of the roof overhang is the same as the external pressure coefficient on the adjacent wall surface, adjusted for effective wind area,determined from Figure 30.4-1 or Figure 30.6-1 as applicable (GC pi) = internal pressure coefficient given in Table 26.11-1 The steps required for the determination of wind loads on components and cladding of roof overhangs are shown in Table 30.10-1. 30.4-2A to 30.4-2C (flat roofs, gable roofs, and hip roofs), including contributions from top and bottom surfaces of overhang. P = q h( GC p) - ( GC pi) (lb/ft 2) (N/m 2) (30.10-1) where q h = velocity pressure from Section 30.3.2 evaluated at mean roof height h using exposure defined in Section 26.7.3 (GC p) = external pressure coefficients for overhangs given in Figs. Leeward parapet pressure (p 4) is determined using the negative wall pressure (p 6) zones 4 or 5 from the applicable figure. For buildings for which these provisions are applicable, this method generally yields the lowest wind pressures of all analytical methods contained in this standard. The provisions in Part 1 are based on the envelope procedure with wind pressures calculated using the specified equation as applicable to each building surface. 30.4-2A to 30.4-2C (flat roofs, gable roofs,and hip roofs) - Figure 30.4-3 (stepped roofs) - Figure 30.4-4 (multispan gable roofs) - Figures 30.4-5A and 30.4-5B (monoslope roofs) - Figure 30.4-6 (sawtooth roofs) - Figure 30.4-7 (domed roofs) - Figure 27.4-3, note 4 (arched roofs) (GC pi) = internal pressure coefficient given in Table 26.11-1 User Note: Use Part 1 of to determine wind pressures on C&C of enclosed and partially enclosed low-rise buildings having roof shapes as specified in the applicable figures. P = q h( GC p) - ( GC pi) (lb/ft 2) (N/m 2) (30.4-1) where q h = velocity pressure evaluated at mean roof height h as defined in (GC p) = external pressure coefficients given in: - Figure 30.4-1 (walls) - Figures. Figure 30.4-2B External Pressure Coefficients, GC p Gable/Hip Roofs 7°.
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