Nonsymmetrical loading of the snow
A decrease in snow weight in some parts of a roof because of the wind, or melting from the heath, or the sun light would reduce internal powers and tensions in parts of the structure. However, there might be some cases that reduction in the amount of snow in some parts of the roof can cause more tension in some other parts of the structure. Cantilever roofs are obvious examples of that. Reduction of the snow weight in some parts of the cantilever causes some flexural tensions and changes in the shapes of the nearby cover of the threshold.
In arched roofs, nonsymmetrical loading would be essential if the gradient of the arch is at least 10 and at most 60.