Allowing building heat to reach roof and melt snow, even on days when the air temperature is below freezing. The melted snow will run down the overhanging eave and freeze again, creating an ever growing ice dam, which will eventually lead to roof damage and leaks.
Using gutters or downspouts without heat trace and in locations where snow can slide and tear them off the building.
Allowing water from a low slope roof to drain over the edge, where it can damage the building.
Using a metal roof or a steep pitched roof without planning for snow shed, allowing snow to shed onto driveways, walkways, or other places where it might endanger life or property.
In this example, vents in the upper portion of the roof are causing snow to melt on the roof. The melting snow is dripping down the roof and causing ice buildups along the eaves. This kind of ice buildup happens when the temperature outside is below freezing, but warmth the house causes snow on the roof to melt and turn to ice.
This is another example of an unsuccessful roof design. Poor roof design is allowing building heat to melt snow, and the melted snow is causing huge icicles at the eaves. The lower roof over the entry was added later to protect pedestrians from falling ice and snow.
This is a metal roof that is not properly shedding snow. Because the roof is not vented, snow on the roof melts even when the temperature is below freezing, and causes buildups of ice that sometimes cover the entire front porch.