Dive summary:

• After recent repeated snowfalls in the nation's midsection and the Northeast, owners of homes and commercial buildings may have been sweating in the cold a little bit wondering how much weight was stressing their roofs.
• Buildings built to modern codes, including the International Building Code, should not have a problem or require shoveling, with loadings of 30 or 35 pounds per square foot required in design and construction.
• What varies widely, however, is the water content of the snow, whether the roof is flat (or almost flat if it is built right) or sloped and "shadow" loads that can blow off higher adjacent roofs onto lower ones.

From the article:

"If you talk to an engineer, and he's doing an evaluation of a building, he's going up there on the building and he's weighing it." ...