A Beginner's Guide to ASCE 705 Chapter 8  S: Snow Loads © 2007, T. Bartlett Quimby 

Section 8.4 Sloped Roof Snow Load, p_{s} Last Revised: 11/04/2014 The sloped roof snow load, p_{s}, is found by multiplying the flat roof snow load, p_{f}, by a slope factor, C_{s}. The value of C_{s} depends on such factors as
The values for C_{s} are obtained from the three graphs found in ASCE 705 Figure 72. Each graph relates to one of the three thermal factor values given in ASCE 705 Table 73. On each graph are two curves. One for "unobstructed slippery surfaces" and one for all other types of surfaces. ASCE 705 7.4.1 provides some minimum insulation values for warm roofs that are to be considered to be unobstructed and slippery. In buildings with insufficient insulation, ice damming on eaves is common, resulting in an obstruction that might not be considered by looking at the design of the roof system. Ice dams may be effective in preventing sliding on otherwise slippery roofs. Figure 8.4.1 shows an obstruction on a slippery roof that turns out to be a drift that formed on an awning over a door way. Note that show up slope from the obstruction is still on the roof while all the rest of the snow has slid off the roof. Figure 8.4.1
High Pitch (slope > 70^{o}) and Curved Roofs For roof slopes exceeding 70^{o}, of any surface type, it is assumed that the snow will slide off the roof.
Measuring Sloped Roof Snow Load 