2001 ASD Supplements - unprotected PDF - American Wood Council

L-58 SPAN TABLESFootnotes to Table 7.121Footnotes to Tables 3.26 A-HTabulated rafter spans assume ceiling joists or rafter ties are located at the bottom of the attic space to resist thrust. When ceilingjoists or rafter ties are located higher in the attic space, the rafter spans shall be multiplied by the factors given in the followingtable:Ceiling Height/Roof Ridge Height(H C /H R )Rafter Span Adjustment FactorsHRH RHCT TTT1/21/31/41/51/61/7.5 and less0.580.670.760.830.901.00Note: Lateral deflection of the rafter below the rafter ties may exceed 3/4 inch when rafter ties are located above onethirdof the ridge height, H r , or when H c is greater than 2 feet and may require additional consideration.2Tabulated rafter spans are based on roof dead and live loads. For Exposure B wind loads, the rafter span adjustment factor, whichshall not exceed 1.0, shall be multiplied times the rafter spans in Table 7.12. For Exposure C, rafter span adjustments shall bemultiplied by 0.8.RAFTER SPAN ADJUSTMENT FOR EXPOSURE B & C WIND LOADSThree Second Gust Wind Speed (mph)Roof Pitch0:121:122:123:124:125:126:127:128:129:1210:1211:1212:1285 90 100 110 120 130 140 150Rafter Span Adjustment Factor for Dual-Pitched Roofs1.18 1.10 0.97 0.87 0.79 0.73 0.67 0.621.17 1.09 0.97 0.87 0.79 0.72 0.67 0.621.16 1.08 0.96 0.86 0.78 0.72 0.66 0.611.34 1.25 1.10 0.98 0.89 0.81 0.75 0.701.30 1.21 1.07 0.96 0.87 0.79 0.73 0.681.24 1.15 1.02 0.91 0.83 0.76 0.70 0.651.17 1.09 0.96 0.86 0.78 0.72 0.66 0.621.52 1.41 1.23 1.09 0.98 0.90 0.82 0.761.42 1.31 1.15 1.02 0.92 0.84 0.78 0.721.32 1.22 1.07 0.96 0.87 0.79 0.73 0.681.22 1.14 1.00 0.89 0.81 0.74 0.68 0.631.14 1.06 0.93 0.84 0.76 0.69 0.64 0.591.06 0.98 0.87 0.78 0.71 0.65 0.60 0.563Tabulated rafter spans in Table 7.12 shall be permitted to be multiplied by the sloped roof adjustment factors in the followingtable, for roof pitches greater than 4:12:20 psf Live, 20 psf Dead 20 psf Live, 20 psf DeadRoof Pitch5:126:127:128:129:1210:1211:1212:12Adjustment Factor for Sloped Roofs1.02 1.011.04 1.031.05 1.041.07 1.051.10 1.071.12 1.081.14 1.101.17 1.12AMERICAN WOOD COUNCIL