Research has shown that sloped roofs covered with pre-painted steel have reduced snow loads relative to roofs covered with asphalt shingles. Sentence 2.3.3.1.(1) allows a reduction of the slope factor, Cs, for unobstructed slippery roofs of farm buildings where the roof slope, α, is greater than 15° but not greater than 60°. Figure A-2.3.3.1.(1) shows the Cs versus α curve calculated in accordance with Sentence 2.3.3.1.(1).
Before using the reduced slope factor, the designer should carefully examine the proposed roof configuration to ensure that snow will freely slide off the roof. The reduced slope factor does not apply to sloped roofs terminating at grade, at a roof valley, or at another roof of lower slope because the snow may pile up or not slide freely at the transition in slope.
The reduced slope factor also does not apply to roofs with obstructions, such as chimneys, silos or ice guards.
