Load combinations (Canadian National Building Code NBC 2020)

[hosambadrawy]

Hello everyone, I have some question regarding load combinations on the (Canadian National Building Code NBC 2020). the code is not differentiating between the live load and roof live load, and I am little confused about the combinations given on able 4.1.3.2.-A and how to apply it on roofs! for example, on combination case 2, are we adding the roof live load together with Snow load meaning ( 1.25D+1.5L "roof" + 1.0 S "roof").
I think there is something not clear because as I understood from Article 4.1.5.5 that the general case is to design the roof on either live load for assembly OR Snow Load.
Can anyone explain, please.

 

[a_urbs]

Sentence 2 in 4.1.5.5 answers your question. Whatever produces the most critical loading, the roof live load or snow and rain. The idea is that the live-load due to people being on the roof is low in comparison to snow, especially in most parts of Canada.

However, it's worth clarifying that this does not apply to rooftop mechanical units, for example, and should be included as live load in addition to snow load, drifts, ponding, etc.

 

[hosambadrawy]

Sentence 2 in 4.1.5.5 answers your question. Whatever produces the most critical loading, the roof live load or snow and rain. The idea is that the live-load due to people being on the roof is low in comparison to snow, especially in most parts of Canada.

However, it's worth clarifying that this does not apply to rooftop mechanical units, for example, and should be included as live load in addition to snow load, drifts, ponding, etc.

Thanks for clarification