The Ontario Building Code | Specified Rain Load
4.1.6.4. Specified Rain Load
(1) Except as provided in Sentence (4), the specified load, S, due to the accumulation of rainwater on a surface whose position, shape and deflection under load make such an accumulation possible, is that resulting from the one-day rainfall determined in conformance with Subsection 1.1.2. and applied over the horizontal projection of the surface and all tributary surfaces.
(2) The provisions of Sentence (1) apply whether or not the surface is provided with a means of drainage, such as rainwater leaders.
(3) Except as provided for in Sentence 4.1.6.2.(1), loads due to rain need not be considered to act simultaneously with loads due to snow.
(4) Where scuppers are provided and where the position, shape and deflection of the loaded surface make an accumulation of rainwater possible, the loads due to rain shall be the lesser of either the one-day rainfall determined in conformance with Subsection 1.1.2. or a depth of rainwater equal to 30 mm above the level of the scuppers, applied over the horizontal projection of the surface and tributary areas.
4.1.7. Wind Load
In Plain Language
Except in specific cases, the specified rain load on a surface prone to water accumulation (due to its shape, position, or deflection under load) must be calculated per the formula in this article, addressing the risk of ponding.
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.