S = Ss(Is)(CbCwCsCa)
Where:
S = Alternate unbalanced roof snow load
Ss = Ground snow load from IBC Figure 1608.2
Is = Importance factor from IBC section 1608.1 [ASCE 7, Table 7-4]
Cb = Basic roof snow load factor of 0.8
Cw = Wind exposure factor of 1.0
Cs = Slope factor; see Tables 362.1608-1 and 362.1608-2
Ca = Accumulation factor; see Table 362.1608-3
Table 362.1608-1
Non-Slippery Roofa
Roof Slope, [ALPHA] | Factor, Cs |
[ALPHA] <= 30° | 1.0 |
30° < [ALPHA] <= 70° | (70° - [ALPHA]) / 40° |
70° < [ALPHA] | 0 |
Table 362.1608-2
Unobstructed Slippery Roofa
Roof Slope, [ALPHA] | Factor, Cs |
[ALPHA] <= 15° | 1.0 |
15° < [ALPHA] <= 60° | (60° - [ALPHA]) / 45° |
60° < [ALPHA] | 0 |
Table 362.1608-3
Accumulation Factor
Roof Slope, [ALPHA] | Factor, Ca |
[ALPHA] <= 15° | N/A. Analysis for balanced loading only. |
15° < [ALPHA] <= 20° | 0.25 + [ALPHA] / 20° |
20° < [ALPHA] <= 90° | 1.25 |
Wis. Admin. Code Department of Safety and Professional Services SPS 362.1608