9.4.2.2. Specified Snow Loads

(See Note A-9.4.2.1. and 9.4.2.2.)

(1)

Except as provided in Sentences (2) and (4), specified snow loads shall be not less than those calculated using the following formula: S = C_b S_s + S_r where S = specified snow load, C_b = basic snow load roof factor, which is 0.45 where the entire width of a roof does not exceed 4.3 m and 0.55 for all other roofs, S_s = 1-in-50 year ground snow load in kPa, determined according to MMAH Supplementary Standard SB-1, “Climatic and Seismic Data,” and S_r = associated 1-in-50 year rain load in kPa, determined according to MMAH Supplementary Standard SB-1, “Climatic and Seismic Data.”

(2)

In no case shall the specified snow load be less than 1 kPa.

(3)

Bow string, arch or semi-circular roof trusses having an unsupported span greater than 6 m shall be designed in conformance with the snow load requirements in Subsection 4.1.6.

(4)

Where the height of a roof step at the intersection of an upper level roof and a lower level roof is greater than 2 m, and the upper level roof has a slope less than 1 in 6 and an area greater than 600 m2, the specified snow load on the lower level roof shall be

(a)

for distances from the roof step that are less than or equal to the drift length, x_d, calculated in accordance with Sentence (5), not less than 1.5 times the specified snow load, S, calculated using the formula in Sentence (1) with C_b equal to 0.55, and

(b)

for distances from the roof step that are greater than the drift length, x_d, calculated in accordance with Sentence (5), as specified in Sentence (1).

(5)

For the purposes of Sentence (4), the drift length, x_d, in m, shall be calculated as follows:

where h = height of the roof step, in m, and γ = specific weight of snow as specified in Clause [[b-9.4.2.1.#^1fhplca|9.4.2.1.(1)(f)]].