The Ontario Building Code | Specified Snow Loads
9.4.2.2. Specified Snow Loads
(1) Except as provided in Sentences (2) and (3), specified snow loads shall be not less than those calculated using the following formula:
S = Cb ∙ Ss+ Sr
where,
S = specified snow load,
Cb = 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,
Ss = 1-in-50 year ground snow load in kPa, determined according to MMAH Supplementary Standard SB-1, "Climatic and Seismic Data", and
Sr = 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.
In Plain Language
Specified snow loads for roofs and other exposed surfaces are calculated per this article, based on factors including ground snow load and roof shape.
This is a plain-language summary of the 2012/2017 Ontario Building Code text above, for general understanding only and not a substitute for the Code. Always confirm current requirements against the 2024 edition (O.Reg. 163/24) or a qualified professional before construction.