this is what i learned:
First we must differentiate between fresh snow, old snow and compact (wet and watery) . The first has a weight ranging between 80 and 200 kg / cu m (cubic meter), the second between 200 and 500 kg / cu m, while the third can be up to 800 kg / cu m. The ice on the other hand is around 900 kg / cu m.
That said, how much they weigh, for example, 20 inches of new snow over an area of one square meter? The calculation is simple: height in meters x specific gravity.
In our case, such as taking specific weight 100 kg / cubic meter, there will be 0.2 meters x 100 lbs = 20 kg (per square meter).
If we wanted to estimate the weight of 60 inches of old snow and wet, should be done for 0.6 meters 400 kg = 240 kg (always per sqm). Almost like having 3 adult men for every square meter. With this load, you're sure that your roof will remain firmly?