How does an ice dam occur?

An ice dam forms primarily when water builds up behind a blockage of ice, which typically occurs when melting snow on a roof cannot escape due to ice that has formed in the gutters or along the roof's edge. As the snow melts from the heat of the house, the water flows down the roof but encounters this blockage, preventing it from draining properly. The accumulated water then backs up behind the ice, creating a dam-like effect. This trapped water can eventually seep under shingles or into the roof structure, leading to potential water damage inside the home.

In this context, understanding how melting snow interacts with freezing temperatures is key, as the transition from liquid to solid creates the blockage that leads to the formation of the ice dam. This explanation provides a clearer understanding of the process, emphasizing the crucial role of melting and subsequent freezing in ice dam formation.