We generally estimate the snow load on the roof of a structure as a function of the snow load expected on the adjacent ground.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
Thank you Koot for your answer. They have 2 listings, one as roof snow (live) load that makes sense, and the other listings is ground snow load. I just cannot see an importance to that second category and how the weight of the snow on the ground affects the building.
If you are located in the USA, the American Society of Civil Engineers (ASCE) publishes a standard, Minimum Design Loads for Buildings and Other Structures (I think, my copies are at the office); ASCE 7-10 is the most recent edition, which has a Ground Snow Load Map by counties and states. This standard has maps which give the Ground Snow Load and formulas to calculate the roof snow load as well as some snow drifts and unbalanced snow loads. Many other countries have similar standards.
There are also web sites which have similar information.
It's a common practice, and sometimes a code requirement, to list the environmental parameters affecting the design loads on the contract documents (ground snow, wind speed, seismic site class). That way, those reviewing the documents can easily understand the context in which the structure has been designed.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
Ok, I feel like this should be said: if you're designing a building and don't understand why you need to know the ground snow load, then perhaps you shouldn't be designing the building. Structural engineering requires a license, at least in the US, and this may be considered operating outside your area of expertise.
Late to comment but it hasn't been mentioned that the ground snow load is not the final roof design snow load due to all the factors that need be applied to the ground snow load to apply to the roof.
Ground snow load is used directly in the calculations for various drifting snow cases. While there is one roof snow calculated (or specified by code) it covers the uniform application only. Any step snow conditions, valley conditions, over-ridge drift conditions, etc. use the original ground snow load value in the formula.
