NBCC Snow and Live Loading on Roof Mechanical Decks

[efFeb]

Good Morning,
I have a rooftop mechanical deck with snow load. In clause 4.1.5.5, we're given guidance on how to combine snow and live loads on accessible roof decks and exterior parking areas, but for a mechanical deck I can't find any real guidance on how to account for snow load. At the units themselves, it would make sense to me to apply the full live load from mechanical equipment, plus base snow load at the unit locations, and then take the worse of assembly loading and snow drift for the deck between units.
If anyone has a different approach that should be used, or a code reference that I might have missed, i'd love any input.
Thanks so much,

 

[canwesteng]

What is the live load on the deck itself? If it's only occupancy for maintenance on the units, then I would use the greater of live and snow drift. If it's likely to be storage than you should use snow and live additively.

 

[Ganesh Persaud]

To be safe you can add the mechanical live and snow live. The asce loaf combination have provisions for these loads. In the load combination the live load (L) on the floor would be your mechanical live and your active live(from persons). The snow load (S) as I’m load combinations are there properly determine the worst case scenario. I’m not sure if this helped you.

 

[r13]

What I would do is, calculate the live load on the area besides the foot print of the equipment, then distribute it on the entire area, or on a localized area, as the active live load. Combine this live load with snow and equipment load using code specified combination.

 

[Liam Nesson]

I haven't got the code with me right now, but i believe one of the load cases has 1.25D+1.5S (+ 1.0L companion load). Somewhere in the notes it says to increase to 1.5L for equipment live loads.

My understanding of roof snow and live loads is that maintenance live load and snow load should not be combined (you should check and verify this either in the code itself, the appendix or the commentary). Assuming snow is 3kN/m3, at 1kpa this equals 1' of snow. You should be cleaning off snow before accessing the roof. At 3kPa of snow (which can happen further up north) that's 1m of snow! Although maintenance live load with snow loads is unlikely, equipment live load with snow load is a real possibility and should be designed for.